From 9a467e4b3568e846288cb5a59668c878ab929771 Mon Sep 17 00:00:00 2001
From: Emmanuel Schanzer <schanzer@ccs.neu.edu>
Date: Fri, 27 Mar 2026 07:54:11 -0500
Subject: [PATCH 1/9] add primitives for vertical- and horizontal-symmetry
 (needed in the library due to performance reasons). Claude Sonnet 4.6 and
 Gemini 3.1 Thinking did the heavy lifting.

---
 src/js/trove/image-lib.js              | 116 +++++++++++++++++--------
 src/js/trove/internal-image-typed.js   |   8 +-
 src/js/trove/internal-image-untyped.js |  14 +--
 src/js/trove/make-image.js             |  14 +++
 tests/pyret/tests/test-images.arr      |  47 ++++++++++
 5 files changed, 156 insertions(+), 43 deletions(-)

diff --git a/src/js/trove/image-lib.js b/src/js/trove/image-lib.js
index f5677f135..516a11428 100644
--- a/src/js/trove/image-lib.js
+++ b/src/js/trove/image-lib.js
@@ -741,14 +741,14 @@
       this.src = src;
       this.ariaText = " video file from "+decodeURIComponent(src).slice(16);
       if (rawVideo) {
-        this.video			= rawVideo;
-        this.width			= self.video.videoWidth;
-        this.height			= self.video.videoHeight;
-        this.video.volume	= 1;
-        this.video.poster	= "http://www.wescheme.org/images/broken.png";
-        this.video.autoplay	= true;
+        this.video      = rawVideo;
+        this.width      = self.video.videoWidth;
+        this.height      = self.video.videoHeight;
+        this.video.volume  = 1;
+        this.video.poster  = "http://www.wescheme.org/images/broken.png";
+        this.video.autoplay  = true;
         this.video.autobuffer=true;
-        this.video.loop		= true;
+        this.video.loop    = true;
         this.video.play();
       } else {
         // fixme: we may want to do something blocking here for
@@ -758,12 +758,12 @@
         this.video = document.createElement('video');
         this.video.src = src;
         this.video.addEventListener('canplay', function() {
-          this.width			= self.video.videoWidth;
-          this.height			= self.video.videoHeight;
-          this.video.poster	= "http://www.wescheme.org/images/broken.png";
-          this.video.autoplay	= true;
+          this.width      = self.video.videoWidth;
+          this.height      = self.video.videoHeight;
+          this.video.poster  = "http://www.wescheme.org/images/broken.png";
+          this.video.autoplay  = true;
           this.video.autobuffer=true;
-          this.video.loop		= true;
+          this.video.loop    = true;
           this.video.play();
         });
         this.video.addEventListener('error', function(e) {
@@ -849,7 +849,7 @@
         var blank = makeCanvas(0, 0);
         return blank;
       }
-        
+
       var ctx = canvas.getContext("2d");
       var width = canvas.width;
       var imageData = ctx.getImageData(0, 0, canvas.width, canvas.height);
@@ -887,7 +887,7 @@
       // start in a coordinate system with origin at top/left corners
       var x1 = 0, y1 = 0, x2 = 0, y2 = 0;
       var anchor1, anchor2;
-      
+
       // compute the x1/y1 and x2/y2 offsets, relative to the top/left of img1/img2:
       switch(placeX1.toLowerCase()) {
       case "left": x1 -= 0; anchor1 = "-left"; break;
@@ -919,10 +919,10 @@
       case "bottom": y2 -= img2.height; anchor2 = "bottom" + anchor2; break;
       default: throw new Error("Unknown YPlace option for image 2: " + placeY2);
       }
-      
+
       // Next, offset x2/y2 by the given offsetX/Y
       x2 += offsetX; y2 += offsetY;
-      
+
 
       // Translate both offset pairs by the smaller of the half-dimensions
       var xMax = Math.max(img1.width, img2.width);
@@ -940,7 +940,7 @@
       var i, v1 = img1.getVertices(), v2 = img2.getVertices(), xs = [], ys = [];
       v1 = v1.map(function(v){ return {x: v.x + x1, y: v.y + y1}; });
       v2 = v2.map(function(v){ return {x: v.x + x2, y: v.y + y2}; });
-        
+
       // store the vertices as something private, so this.getVertices() will still return undefined
       this._vertices = v1.concat(v2);
 
@@ -1277,7 +1277,7 @@
               this.width     === other.width     &&
               this.height    === other.height    &&
               this.direction === other.direction &&
-              imageEquals(this.img, other.img) ) 
+              imageEquals(this.img, other.img) )
             || BaseImage.prototype.equals.call(this, other);
     };
 
@@ -1390,7 +1390,7 @@
         vertices[v].y = jsnums.toFixnum(vertices[v].y);
         vertices[v].y *= -1;
       }
-      
+
       this.width      = findWidth(vertices);
       this.height     = findHeight(vertices);
       this.style      = style;
@@ -1408,7 +1408,7 @@
       this.ariaText = " a"+colorToSpokenString(color,style) + ", polygon with "+vertices.length+" points";
     };
     PointPolygonImage.prototype = heir(BaseImage.prototype);
-    
+
 
     // We don't trust ctx.measureText, since (a) it's buggy and (b) it doesn't measure height
     // based off of https://stackoverflow.com/a/9847841/783424,
@@ -1432,7 +1432,7 @@
       var block = document.createElement("div");
       block.style.display = "inline-block";
       block.style.width = 1; block.style.height = 0;
-      block.style.margin = "0"; block.style.padding = "0";      
+      block.style.margin = "0"; block.style.padding = "0";
       var div = document.createElement("div");
       div.style.margin = "0"; div.style.padding = "0";
       div.append(text, block);
@@ -1754,11 +1754,57 @@
       this.pinholeX = Math.abs(x) / 2;
       this.pinholeY = Math.abs(y) / 2;
       this.ariaText = " a" + colorToSpokenString(color,'solid') + " line of width "+x+" and height "+y;
-      
+
     };
 
     LineImage.prototype = heir(BaseImage.prototype);
 
+    var verticalSymmetry = function(img) {
+      var width  = img.getWidth();
+      var height = img.getHeight();
+      var halfW  = Math.floor(width / 2);
+      if (halfW === 0 || height === 0) { return 1; }
+      var canvas = makeCanvas(width, height);
+      img.render(canvas.getContext("2d"));
+      var data = canvas.getContext("2d").getImageData(0, 0, width, height).data;
+      var sumSq = 0, count = 0;
+      for (var y = 0; y < height; y++) {
+        for (var x = 0; x < halfW; x++) {
+          var i1 = (y * width + x) * 4;
+          var i2 = (y * width + (width - 1 - x)) * 4;
+          for (var ch = 0; ch < 4; ch++) {
+            var d = data[i1 + ch] - data[i2 + ch];
+            sumSq += d * d;
+          }
+          count += 4;
+        }
+      }
+      return 1 - Math.sqrt(sumSq / count) / 255;
+    };
+
+    var horizontalSymmetry = function(img) {
+      var width  = img.getWidth();
+      var height = img.getHeight();
+      var halfH  = Math.floor(height / 2);
+      if (width === 0 || halfH === 0) { return 1; }
+      var canvas = makeCanvas(width, height);
+      img.render(canvas.getContext("2d"));
+      var data = canvas.getContext("2d").getImageData(0, 0, width, height).data;
+      var sumSq = 0, count = 0;
+      for (var y = 0; y < halfH; y++) {
+        for (var x = 0; x < width; x++) {
+          var i1 = (y * width + x) * 4;
+          var i2 = ((height - 1 - y) * width + x) * 4;
+          for (var ch = 0; ch < 4; ch++) {
+            var d = data[i1 + ch] - data[i2 + ch];
+            sumSq += d * d;
+          }
+          count += 4;
+        }
+      }
+      return 1 - Math.sqrt(sumSq / count) / 255;
+    };
+
     var colorAtPosition = function(img, x, y) {
       var width = img.getWidth(),
       height = img.getHeight(),
@@ -1902,26 +1948,26 @@
     var isSceneImage = function(x) { return x instanceof SceneImage; };
     var isCircleImage = function(x) { return x instanceof EllipseImage &&
                                       x.width === x.height; };
-    var isStarImage	= function(x) { return x instanceof StarImage; };
+    var isStarImage  = function(x) { return x instanceof StarImage; };
     var isRectangleImage=function(x) { return x instanceof RectangleImage; };
     var isRegularPolygonImage = function(x) { return x instanceof RegularPolygonImage; };
     var isPointPolygonImage = function(x) { return x instanceof PointPolygonImage; };
     var isRhombusImage = function(x) { return x instanceof RhombusImage; };
-    var isSquareImage	= function(x) { return x instanceof SquareImage; };
+    var isSquareImage  = function(x) { return x instanceof SquareImage; };
     var isTriangleImage= function(x) { return x instanceof TriangleImage; };
     var isWedgeImage = function(x) { return x instanceof WedgeImage; };
     var isEllipseImage = function(x) { return x instanceof EllipseImage; };
-    var isLineImage	= function(x) { return x instanceof LineImage; };
+    var isLineImage  = function(x) { return x instanceof LineImage; };
     var isOverlayImage = function(x) { return x instanceof OverlayImage; };
-    var isRotateImage	= function(x) { return x instanceof RotateImage; };
-    var isScaleImage	= function(x) { return x instanceof ScaleImage; };
-    var isCropImage	= function(x) { return x instanceof CropImage; };
-    var isFrameImage	= function(x) { return x instanceof FrameImage; };
-    var isPinholeImage	= function(x) { return x instanceof PinholeImage; };
-    var isFlipImage	= function(x) { return x instanceof FlipImage; };
-    var isTextImage	= function(x) { return x instanceof TextImage; };
-    var isFileImage	= function(x) { return x instanceof FileImage; };
-    var isFileVideo	= function(x) { return x instanceof FileVideo; };
+    var isRotateImage  = function(x) { return x instanceof RotateImage; };
+    var isScaleImage  = function(x) { return x instanceof ScaleImage; };
+    var isCropImage  = function(x) { return x instanceof CropImage; };
+    var isFrameImage  = function(x) { return x instanceof FrameImage; };
+    var isPinholeImage  = function(x) { return x instanceof PinholeImage; };
+    var isFlipImage  = function(x) { return x instanceof FlipImage; };
+    var isTextImage  = function(x) { return x instanceof TextImage; };
+    var isFileImage  = function(x) { return x instanceof FileImage; };
+    var isFileVideo  = function(x) { return x instanceof FileVideo; };
 
     ///////////////////////////////////////////////////////////////
     // Exports
@@ -1989,6 +2035,8 @@
 
         colorAtPosition: colorAtPosition,
         imageToColorList: imageToColorList,
+        verticalSymmetry: verticalSymmetry,
+        horizontalSymmetry: horizontalSymmetry,
         colorListToImage: colorListToImage,
         trimCanvas: trimCanvas,
         trimImageToCanvas: trimImageToCanvas,
diff --git a/src/js/trove/internal-image-typed.js b/src/js/trove/internal-image-typed.js
index 84226d468..87ab42e78 100644
--- a/src/js/trove/internal-image-typed.js
+++ b/src/js/trove/internal-image-typed.js
@@ -154,6 +154,8 @@
       "image-width": ["arrow", ["Image"], "Number"],
       "image-height": ["arrow", ["Image"], "Number"],
       "image-baseline": ["arrow", ["Image"], "Number"],
+      "vertical-symmetry": ["arrow", ["Image"], "Number"],
+      "horizontal-symmetry": ["arrow", ["Image"], "Number"],
       "image-pinhole-x": ["arrow", ["Image"], "Number"],
       "image-pinhole-y": ["arrow", ["Image"], "Number"],
       "name-to-color": ["arrow", ["String"], "OptColor"],
@@ -223,7 +225,7 @@
       }
       return { x: jsnums.toFixnum(gf(val, "x")), y: jsnums.toFixnum(gf(val, "y")) };
     };
-    
+
     const ANNOTS = {
       annString: runtime.String,
       annNumber: runtime.Number,
@@ -264,7 +266,7 @@
           "ff-symbol":     function(_) { return "symbol"; },
           "ff-system":     function(_) { return "system"; },
         });
-      },   
+      },
       annFontStyle: image.annFontStyle,
       unwrapFontStyle: function(fs) {
         return runtime.ffi.cases(pyAlwaysTrue, "FontStyle", fs, {
@@ -358,4 +360,4 @@
         "Scene": runtime.makePrimitiveAnn("Scene", checkScenePred)
       });
   }
-})
+})
\ No newline at end of file
diff --git a/src/js/trove/internal-image-untyped.js b/src/js/trove/internal-image-untyped.js
index 8103ca5c9..0bd9c7dcc 100644
--- a/src/js/trove/internal-image-untyped.js
+++ b/src/js/trove/internal-image-untyped.js
@@ -143,6 +143,8 @@
       "color-list-to-bitmap": ["arrow", ["LoC", "Number", "Number"], "Image"],
       "image-width": ["arrow", ["Image"], "Number"],
       "image-height": ["arrow", ["Image"], "Number"],
+      "vertical-symmetry": ["arrow", ["Image"], "Number"],
+      "horizontal-symmetry": ["arrow", ["Image"], "Number"],
       "image-baseline": ["arrow", ["Image"], "Number"],
       "image-pinhole-x": ["arrow", ["Image"], "Number"],
       "image-pinhole-y": ["arrow", ["Image"], "Number"],
@@ -194,7 +196,7 @@
     };
     var isPlaceY = function(x) {
       return (isString(x) &&
-              (x.toString().toLowerCase() == "top"	  ||
+              (x.toString().toLowerCase() == "top"    ||
                x.toString().toLowerCase() == "bottom"   ||
                x.toString().toLowerCase() == "baseline" ||
                x.toString().toLowerCase() == "center"   ||
@@ -284,7 +286,7 @@
                  x.toString().toLowerCase() == "modern" ||
                  x.toString().toLowerCase() == "symbol" ||
                  x.toString().toLowerCase() == "system"))
-          || (x === false);		// false is also acceptable
+          || (x === false);    // false is also acceptable
       }),
       unwrapFontFamily: identity,
       annFontStyle: ann("Font Style (\"normal\", \"italic\", or \"slant\")", function(x){
@@ -292,7 +294,7 @@
                 (x.toString().toLowerCase() == "normal" ||
                  x.toString().toLowerCase() == "italic" ||
                  x.toString().toLowerCase() == "slant"))
-          || (x === false);		// false is also acceptable
+          || (x === false);    // false is also acceptable
       }),
       unwrapFontStyle: identity,
       annFontWeight: ann("Font Weight", function(x){
@@ -300,7 +302,7 @@
                 (x.toString().toLowerCase() == "normal" ||
                  x.toString().toLowerCase() == "bold" ||
                  x.toString().toLowerCase() == "light"))
-          || (x === false);		// false is also acceptable
+          || (x === false);    // false is also acceptable
       }),
       unwrapFontWeight: identity,
       annPlaceX: ann("X Place (\"left\", \"middle\", \"center\", \"pinhole\", or \"right\")", isPlaceX),
@@ -367,10 +369,10 @@
     });
 
 
-    
+
     return runtime.makeModuleReturn(values, {
         "Image": image.Image,
         "Scene": runtime.makePrimitiveAnn("Scene", checkScenePred)
       });
   }
-})
+})
\ No newline at end of file
diff --git a/src/js/trove/make-image.js b/src/js/trove/make-image.js
index 3ed32b12e..957637d0c 100644
--- a/src/js/trove/make-image.js
+++ b/src/js/trove/make-image.js
@@ -1273,6 +1273,20 @@
         return runtime.wrap(img.getHeight());
       });
 
+      f("vertical-symmetry", function(maybeImg) {
+        checkArity(1, arguments, "vertical-symmetry", false);
+        c1("vertical-symmetry", maybeImg, annImage);
+        var img = unwrapImage(maybeImg);
+        return runtime.wrap(image.verticalSymmetry(img));
+      });
+
+      f("horizontal-symmetry", function(maybeImg) {
+        checkArity(1, arguments, "horizontal-symmetry", false);
+        c1("horizontal-symmetry", maybeImg, annImage);
+        var img = unwrapImage(maybeImg);
+        return runtime.wrap(image.horizontalSymmetry(img));
+      });
+
       f("image-baseline", function(maybeImg) {
         checkArity(1, arguments, "image-baseline", false);
         c1("image-baseline", maybeImg, annImage);
diff --git a/tests/pyret/tests/test-images.arr b/tests/pyret/tests/test-images.arr
index 63c1d8b84..b53ad2ec4 100644
--- a/tests/pyret/tests/test-images.arr
+++ b/tests/pyret/tests/test-images.arr
@@ -253,3 +253,50 @@ logo2 = image-file("pyret-logo-copy.png")
 check:
   logo is logo2
 end
+
+
+check "Symmetry":
+  fun less-than(n1, n2): n1 < n2 end
+
+  # A simple square should be perfectly symmetrical in both directions
+  perfect-sym = square(50, mode-solid, blue)
+  vertical-symmetry(perfect-sym) is%(within-abs(0.01)) 1
+  horizontal-symmetry(perfect-sym) is%(within-abs(0.01)) 1
+
+  # Two different-colored shapes beside each other break vertical symmetry (left vs right)
+  # but maintain horizontal symmetry (top vs bottom)
+  asym-vert = beside(square(20, mode-solid, red), square(20, mode-solid, blue))
+  vertical-symmetry(asym-vert) is%(less-than) 1
+  horizontal-symmetry(asym-vert) is%(within-abs(0.01)) 1
+
+  # Two different-colored shapes above each other break horizontal symmetry (top vs bottom)
+  # but maintain vertical symmetry (left vs right)
+  asym-horiz = above(square(20, mode-solid, red), square(20, mode-solid, blue))
+  vertical-symmetry(asym-horiz) is%(within-abs(0.01)) 1
+  horizontal-symmetry(asym-horiz) is%(less-than) 1
+
+  # A right triangle is typically asymmetrical in both dimensions
+  rt = right-triangle(40, 50, mode-solid, black)
+  (vertical-symmetry(rt) < 1) is%(within-abs(0.01)) true
+  (horizontal-symmetry(rt) < 1) is%(within-abs(0.01)) true
+
+  # Empty scenes should be perfectly symmetrical
+  empty-sn = empty-scene(50, 50)
+  vertical-symmetry(empty-sn) is%(within-abs(0.01)) 1
+  horizontal-symmetry(empty-sn) is%(within-abs(0.01)) 1
+
+  # Truly empty/0-width or 0-height images should also be symmetrical
+  empty-width = rectangle(0, 100, mode-solid, black)
+  vertical-symmetry(empty-width) is%(within-abs(0.01)) 1
+  horizontal-symmetry(empty-width) is%(within-abs(0.01)) 1
+
+  # Create an asymmetrical image to test cropping
+  asym-base = beside(square(40, mode-solid, red), square(40, mode-solid, blue))
+  vertical-symmetry(asym-base) is%(less-than) 1
+  horizontal-symmetry(asym-base) is%(within-abs(0.01)) 1
+
+  # Cropping just the left side (the red square) restores vertical symmetry
+  cropped-sym = crop(0, 0, 40, 40, asym-base)
+  vertical-symmetry(cropped-sym) is%(within-abs(0.01)) 1
+  horizontal-symmetry(cropped-sym) is%(within-abs(0.01)) 1
+end
\ No newline at end of file

From 81cb2abd45ab9877242657fdf5d736d6159e4a16 Mon Sep 17 00:00:00 2001
From: Emmanuel Schanzer <schanzer@ccs.neu.edu>
Date: Fri, 27 Mar 2026 08:37:50 -0500
Subject: [PATCH 2/9] expose new primitives

---
 src/arr/trove/starter2024.arr | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/arr/trove/starter2024.arr b/src/arr/trove/starter2024.arr
index 91d59d48d..acea39d40 100644
--- a/src/arr/trove/starter2024.arr
+++ b/src/arr/trove/starter2024.arr
@@ -235,6 +235,8 @@ provide from I:
   underlay-align-list,
   underlay-list,
   underlay-xy,
+  vertical-symmetry,
+  horizontal-symmetry,
   wedge,
   x-center,
   x-left,

From d67b4397d925d2c95df9e77a942eec5f88aadc42 Mon Sep 17 00:00:00 2001
From: Emmanuel Schanzer <schanzer@ccs.neu.edu>
Date: Fri, 27 Mar 2026 10:29:18 -0500
Subject: [PATCH 3/9] Revert "add primitives for vertical- and
 horizontal-symmetry (needed in the library due to performance reasons).
 Claude Sonnet 4.6 and Gemini 3.1 Thinking did the heavy lifting."

This reverts commit 9a467e4b3568e846288cb5a59668c878ab929771.
---
 src/js/trove/image-lib.js              | 116 ++++++++-----------------
 src/js/trove/internal-image-typed.js   |   8 +-
 src/js/trove/internal-image-untyped.js |  14 ++-
 src/js/trove/make-image.js             |  14 ---
 tests/pyret/tests/test-images.arr      |  47 ----------
 5 files changed, 43 insertions(+), 156 deletions(-)

diff --git a/src/js/trove/image-lib.js b/src/js/trove/image-lib.js
index 516a11428..f5677f135 100644
--- a/src/js/trove/image-lib.js
+++ b/src/js/trove/image-lib.js
@@ -741,14 +741,14 @@
       this.src = src;
       this.ariaText = " video file from "+decodeURIComponent(src).slice(16);
       if (rawVideo) {
-        this.video      = rawVideo;
-        this.width      = self.video.videoWidth;
-        this.height      = self.video.videoHeight;
-        this.video.volume  = 1;
-        this.video.poster  = "http://www.wescheme.org/images/broken.png";
-        this.video.autoplay  = true;
+        this.video			= rawVideo;
+        this.width			= self.video.videoWidth;
+        this.height			= self.video.videoHeight;
+        this.video.volume	= 1;
+        this.video.poster	= "http://www.wescheme.org/images/broken.png";
+        this.video.autoplay	= true;
         this.video.autobuffer=true;
-        this.video.loop    = true;
+        this.video.loop		= true;
         this.video.play();
       } else {
         // fixme: we may want to do something blocking here for
@@ -758,12 +758,12 @@
         this.video = document.createElement('video');
         this.video.src = src;
         this.video.addEventListener('canplay', function() {
-          this.width      = self.video.videoWidth;
-          this.height      = self.video.videoHeight;
-          this.video.poster  = "http://www.wescheme.org/images/broken.png";
-          this.video.autoplay  = true;
+          this.width			= self.video.videoWidth;
+          this.height			= self.video.videoHeight;
+          this.video.poster	= "http://www.wescheme.org/images/broken.png";
+          this.video.autoplay	= true;
           this.video.autobuffer=true;
-          this.video.loop    = true;
+          this.video.loop		= true;
           this.video.play();
         });
         this.video.addEventListener('error', function(e) {
@@ -849,7 +849,7 @@
         var blank = makeCanvas(0, 0);
         return blank;
       }
-
+        
       var ctx = canvas.getContext("2d");
       var width = canvas.width;
       var imageData = ctx.getImageData(0, 0, canvas.width, canvas.height);
@@ -887,7 +887,7 @@
       // start in a coordinate system with origin at top/left corners
       var x1 = 0, y1 = 0, x2 = 0, y2 = 0;
       var anchor1, anchor2;
-
+      
       // compute the x1/y1 and x2/y2 offsets, relative to the top/left of img1/img2:
       switch(placeX1.toLowerCase()) {
       case "left": x1 -= 0; anchor1 = "-left"; break;
@@ -919,10 +919,10 @@
       case "bottom": y2 -= img2.height; anchor2 = "bottom" + anchor2; break;
       default: throw new Error("Unknown YPlace option for image 2: " + placeY2);
       }
-
+      
       // Next, offset x2/y2 by the given offsetX/Y
       x2 += offsetX; y2 += offsetY;
-
+      
 
       // Translate both offset pairs by the smaller of the half-dimensions
       var xMax = Math.max(img1.width, img2.width);
@@ -940,7 +940,7 @@
       var i, v1 = img1.getVertices(), v2 = img2.getVertices(), xs = [], ys = [];
       v1 = v1.map(function(v){ return {x: v.x + x1, y: v.y + y1}; });
       v2 = v2.map(function(v){ return {x: v.x + x2, y: v.y + y2}; });
-
+        
       // store the vertices as something private, so this.getVertices() will still return undefined
       this._vertices = v1.concat(v2);
 
@@ -1277,7 +1277,7 @@
               this.width     === other.width     &&
               this.height    === other.height    &&
               this.direction === other.direction &&
-              imageEquals(this.img, other.img) )
+              imageEquals(this.img, other.img) ) 
             || BaseImage.prototype.equals.call(this, other);
     };
 
@@ -1390,7 +1390,7 @@
         vertices[v].y = jsnums.toFixnum(vertices[v].y);
         vertices[v].y *= -1;
       }
-
+      
       this.width      = findWidth(vertices);
       this.height     = findHeight(vertices);
       this.style      = style;
@@ -1408,7 +1408,7 @@
       this.ariaText = " a"+colorToSpokenString(color,style) + ", polygon with "+vertices.length+" points";
     };
     PointPolygonImage.prototype = heir(BaseImage.prototype);
-
+    
 
     // We don't trust ctx.measureText, since (a) it's buggy and (b) it doesn't measure height
     // based off of https://stackoverflow.com/a/9847841/783424,
@@ -1432,7 +1432,7 @@
       var block = document.createElement("div");
       block.style.display = "inline-block";
       block.style.width = 1; block.style.height = 0;
-      block.style.margin = "0"; block.style.padding = "0";
+      block.style.margin = "0"; block.style.padding = "0";      
       var div = document.createElement("div");
       div.style.margin = "0"; div.style.padding = "0";
       div.append(text, block);
@@ -1754,57 +1754,11 @@
       this.pinholeX = Math.abs(x) / 2;
       this.pinholeY = Math.abs(y) / 2;
       this.ariaText = " a" + colorToSpokenString(color,'solid') + " line of width "+x+" and height "+y;
-
+      
     };
 
     LineImage.prototype = heir(BaseImage.prototype);
 
-    var verticalSymmetry = function(img) {
-      var width  = img.getWidth();
-      var height = img.getHeight();
-      var halfW  = Math.floor(width / 2);
-      if (halfW === 0 || height === 0) { return 1; }
-      var canvas = makeCanvas(width, height);
-      img.render(canvas.getContext("2d"));
-      var data = canvas.getContext("2d").getImageData(0, 0, width, height).data;
-      var sumSq = 0, count = 0;
-      for (var y = 0; y < height; y++) {
-        for (var x = 0; x < halfW; x++) {
-          var i1 = (y * width + x) * 4;
-          var i2 = (y * width + (width - 1 - x)) * 4;
-          for (var ch = 0; ch < 4; ch++) {
-            var d = data[i1 + ch] - data[i2 + ch];
-            sumSq += d * d;
-          }
-          count += 4;
-        }
-      }
-      return 1 - Math.sqrt(sumSq / count) / 255;
-    };
-
-    var horizontalSymmetry = function(img) {
-      var width  = img.getWidth();
-      var height = img.getHeight();
-      var halfH  = Math.floor(height / 2);
-      if (width === 0 || halfH === 0) { return 1; }
-      var canvas = makeCanvas(width, height);
-      img.render(canvas.getContext("2d"));
-      var data = canvas.getContext("2d").getImageData(0, 0, width, height).data;
-      var sumSq = 0, count = 0;
-      for (var y = 0; y < halfH; y++) {
-        for (var x = 0; x < width; x++) {
-          var i1 = (y * width + x) * 4;
-          var i2 = ((height - 1 - y) * width + x) * 4;
-          for (var ch = 0; ch < 4; ch++) {
-            var d = data[i1 + ch] - data[i2 + ch];
-            sumSq += d * d;
-          }
-          count += 4;
-        }
-      }
-      return 1 - Math.sqrt(sumSq / count) / 255;
-    };
-
     var colorAtPosition = function(img, x, y) {
       var width = img.getWidth(),
       height = img.getHeight(),
@@ -1948,26 +1902,26 @@
     var isSceneImage = function(x) { return x instanceof SceneImage; };
     var isCircleImage = function(x) { return x instanceof EllipseImage &&
                                       x.width === x.height; };
-    var isStarImage  = function(x) { return x instanceof StarImage; };
+    var isStarImage	= function(x) { return x instanceof StarImage; };
     var isRectangleImage=function(x) { return x instanceof RectangleImage; };
     var isRegularPolygonImage = function(x) { return x instanceof RegularPolygonImage; };
     var isPointPolygonImage = function(x) { return x instanceof PointPolygonImage; };
     var isRhombusImage = function(x) { return x instanceof RhombusImage; };
-    var isSquareImage  = function(x) { return x instanceof SquareImage; };
+    var isSquareImage	= function(x) { return x instanceof SquareImage; };
     var isTriangleImage= function(x) { return x instanceof TriangleImage; };
     var isWedgeImage = function(x) { return x instanceof WedgeImage; };
     var isEllipseImage = function(x) { return x instanceof EllipseImage; };
-    var isLineImage  = function(x) { return x instanceof LineImage; };
+    var isLineImage	= function(x) { return x instanceof LineImage; };
     var isOverlayImage = function(x) { return x instanceof OverlayImage; };
-    var isRotateImage  = function(x) { return x instanceof RotateImage; };
-    var isScaleImage  = function(x) { return x instanceof ScaleImage; };
-    var isCropImage  = function(x) { return x instanceof CropImage; };
-    var isFrameImage  = function(x) { return x instanceof FrameImage; };
-    var isPinholeImage  = function(x) { return x instanceof PinholeImage; };
-    var isFlipImage  = function(x) { return x instanceof FlipImage; };
-    var isTextImage  = function(x) { return x instanceof TextImage; };
-    var isFileImage  = function(x) { return x instanceof FileImage; };
-    var isFileVideo  = function(x) { return x instanceof FileVideo; };
+    var isRotateImage	= function(x) { return x instanceof RotateImage; };
+    var isScaleImage	= function(x) { return x instanceof ScaleImage; };
+    var isCropImage	= function(x) { return x instanceof CropImage; };
+    var isFrameImage	= function(x) { return x instanceof FrameImage; };
+    var isPinholeImage	= function(x) { return x instanceof PinholeImage; };
+    var isFlipImage	= function(x) { return x instanceof FlipImage; };
+    var isTextImage	= function(x) { return x instanceof TextImage; };
+    var isFileImage	= function(x) { return x instanceof FileImage; };
+    var isFileVideo	= function(x) { return x instanceof FileVideo; };
 
     ///////////////////////////////////////////////////////////////
     // Exports
@@ -2035,8 +1989,6 @@
 
         colorAtPosition: colorAtPosition,
         imageToColorList: imageToColorList,
-        verticalSymmetry: verticalSymmetry,
-        horizontalSymmetry: horizontalSymmetry,
         colorListToImage: colorListToImage,
         trimCanvas: trimCanvas,
         trimImageToCanvas: trimImageToCanvas,
diff --git a/src/js/trove/internal-image-typed.js b/src/js/trove/internal-image-typed.js
index 87ab42e78..84226d468 100644
--- a/src/js/trove/internal-image-typed.js
+++ b/src/js/trove/internal-image-typed.js
@@ -154,8 +154,6 @@
       "image-width": ["arrow", ["Image"], "Number"],
       "image-height": ["arrow", ["Image"], "Number"],
       "image-baseline": ["arrow", ["Image"], "Number"],
-      "vertical-symmetry": ["arrow", ["Image"], "Number"],
-      "horizontal-symmetry": ["arrow", ["Image"], "Number"],
       "image-pinhole-x": ["arrow", ["Image"], "Number"],
       "image-pinhole-y": ["arrow", ["Image"], "Number"],
       "name-to-color": ["arrow", ["String"], "OptColor"],
@@ -225,7 +223,7 @@
       }
       return { x: jsnums.toFixnum(gf(val, "x")), y: jsnums.toFixnum(gf(val, "y")) };
     };
-
+    
     const ANNOTS = {
       annString: runtime.String,
       annNumber: runtime.Number,
@@ -266,7 +264,7 @@
           "ff-symbol":     function(_) { return "symbol"; },
           "ff-system":     function(_) { return "system"; },
         });
-      },
+      },   
       annFontStyle: image.annFontStyle,
       unwrapFontStyle: function(fs) {
         return runtime.ffi.cases(pyAlwaysTrue, "FontStyle", fs, {
@@ -360,4 +358,4 @@
         "Scene": runtime.makePrimitiveAnn("Scene", checkScenePred)
       });
   }
-})
\ No newline at end of file
+})
diff --git a/src/js/trove/internal-image-untyped.js b/src/js/trove/internal-image-untyped.js
index 0bd9c7dcc..8103ca5c9 100644
--- a/src/js/trove/internal-image-untyped.js
+++ b/src/js/trove/internal-image-untyped.js
@@ -143,8 +143,6 @@
       "color-list-to-bitmap": ["arrow", ["LoC", "Number", "Number"], "Image"],
       "image-width": ["arrow", ["Image"], "Number"],
       "image-height": ["arrow", ["Image"], "Number"],
-      "vertical-symmetry": ["arrow", ["Image"], "Number"],
-      "horizontal-symmetry": ["arrow", ["Image"], "Number"],
       "image-baseline": ["arrow", ["Image"], "Number"],
       "image-pinhole-x": ["arrow", ["Image"], "Number"],
       "image-pinhole-y": ["arrow", ["Image"], "Number"],
@@ -196,7 +194,7 @@
     };
     var isPlaceY = function(x) {
       return (isString(x) &&
-              (x.toString().toLowerCase() == "top"    ||
+              (x.toString().toLowerCase() == "top"	  ||
                x.toString().toLowerCase() == "bottom"   ||
                x.toString().toLowerCase() == "baseline" ||
                x.toString().toLowerCase() == "center"   ||
@@ -286,7 +284,7 @@
                  x.toString().toLowerCase() == "modern" ||
                  x.toString().toLowerCase() == "symbol" ||
                  x.toString().toLowerCase() == "system"))
-          || (x === false);    // false is also acceptable
+          || (x === false);		// false is also acceptable
       }),
       unwrapFontFamily: identity,
       annFontStyle: ann("Font Style (\"normal\", \"italic\", or \"slant\")", function(x){
@@ -294,7 +292,7 @@
                 (x.toString().toLowerCase() == "normal" ||
                  x.toString().toLowerCase() == "italic" ||
                  x.toString().toLowerCase() == "slant"))
-          || (x === false);    // false is also acceptable
+          || (x === false);		// false is also acceptable
       }),
       unwrapFontStyle: identity,
       annFontWeight: ann("Font Weight", function(x){
@@ -302,7 +300,7 @@
                 (x.toString().toLowerCase() == "normal" ||
                  x.toString().toLowerCase() == "bold" ||
                  x.toString().toLowerCase() == "light"))
-          || (x === false);    // false is also acceptable
+          || (x === false);		// false is also acceptable
       }),
       unwrapFontWeight: identity,
       annPlaceX: ann("X Place (\"left\", \"middle\", \"center\", \"pinhole\", or \"right\")", isPlaceX),
@@ -369,10 +367,10 @@
     });
 
 
-
+    
     return runtime.makeModuleReturn(values, {
         "Image": image.Image,
         "Scene": runtime.makePrimitiveAnn("Scene", checkScenePred)
       });
   }
-})
\ No newline at end of file
+})
diff --git a/src/js/trove/make-image.js b/src/js/trove/make-image.js
index 957637d0c..3ed32b12e 100644
--- a/src/js/trove/make-image.js
+++ b/src/js/trove/make-image.js
@@ -1273,20 +1273,6 @@
         return runtime.wrap(img.getHeight());
       });
 
-      f("vertical-symmetry", function(maybeImg) {
-        checkArity(1, arguments, "vertical-symmetry", false);
-        c1("vertical-symmetry", maybeImg, annImage);
-        var img = unwrapImage(maybeImg);
-        return runtime.wrap(image.verticalSymmetry(img));
-      });
-
-      f("horizontal-symmetry", function(maybeImg) {
-        checkArity(1, arguments, "horizontal-symmetry", false);
-        c1("horizontal-symmetry", maybeImg, annImage);
-        var img = unwrapImage(maybeImg);
-        return runtime.wrap(image.horizontalSymmetry(img));
-      });
-
       f("image-baseline", function(maybeImg) {
         checkArity(1, arguments, "image-baseline", false);
         c1("image-baseline", maybeImg, annImage);
diff --git a/tests/pyret/tests/test-images.arr b/tests/pyret/tests/test-images.arr
index b53ad2ec4..63c1d8b84 100644
--- a/tests/pyret/tests/test-images.arr
+++ b/tests/pyret/tests/test-images.arr
@@ -253,50 +253,3 @@ logo2 = image-file("pyret-logo-copy.png")
 check:
   logo is logo2
 end
-
-
-check "Symmetry":
-  fun less-than(n1, n2): n1 < n2 end
-
-  # A simple square should be perfectly symmetrical in both directions
-  perfect-sym = square(50, mode-solid, blue)
-  vertical-symmetry(perfect-sym) is%(within-abs(0.01)) 1
-  horizontal-symmetry(perfect-sym) is%(within-abs(0.01)) 1
-
-  # Two different-colored shapes beside each other break vertical symmetry (left vs right)
-  # but maintain horizontal symmetry (top vs bottom)
-  asym-vert = beside(square(20, mode-solid, red), square(20, mode-solid, blue))
-  vertical-symmetry(asym-vert) is%(less-than) 1
-  horizontal-symmetry(asym-vert) is%(within-abs(0.01)) 1
-
-  # Two different-colored shapes above each other break horizontal symmetry (top vs bottom)
-  # but maintain vertical symmetry (left vs right)
-  asym-horiz = above(square(20, mode-solid, red), square(20, mode-solid, blue))
-  vertical-symmetry(asym-horiz) is%(within-abs(0.01)) 1
-  horizontal-symmetry(asym-horiz) is%(less-than) 1
-
-  # A right triangle is typically asymmetrical in both dimensions
-  rt = right-triangle(40, 50, mode-solid, black)
-  (vertical-symmetry(rt) < 1) is%(within-abs(0.01)) true
-  (horizontal-symmetry(rt) < 1) is%(within-abs(0.01)) true
-
-  # Empty scenes should be perfectly symmetrical
-  empty-sn = empty-scene(50, 50)
-  vertical-symmetry(empty-sn) is%(within-abs(0.01)) 1
-  horizontal-symmetry(empty-sn) is%(within-abs(0.01)) 1
-
-  # Truly empty/0-width or 0-height images should also be symmetrical
-  empty-width = rectangle(0, 100, mode-solid, black)
-  vertical-symmetry(empty-width) is%(within-abs(0.01)) 1
-  horizontal-symmetry(empty-width) is%(within-abs(0.01)) 1
-
-  # Create an asymmetrical image to test cropping
-  asym-base = beside(square(40, mode-solid, red), square(40, mode-solid, blue))
-  vertical-symmetry(asym-base) is%(less-than) 1
-  horizontal-symmetry(asym-base) is%(within-abs(0.01)) 1
-
-  # Cropping just the left side (the red square) restores vertical symmetry
-  cropped-sym = crop(0, 0, 40, 40, asym-base)
-  vertical-symmetry(cropped-sym) is%(within-abs(0.01)) 1
-  horizontal-symmetry(cropped-sym) is%(within-abs(0.01)) 1
-end
\ No newline at end of file

From a33f7c7efa1b691354706ceb1432bdb7fecc151a Mon Sep 17 00:00:00 2001
From: Emmanuel Schanzer <schanzer@ccs.neu.edu>
Date: Fri, 27 Mar 2026 10:46:52 -0500
Subject: [PATCH 4/9] re-do the changes without all the whitespace bullshit

---
 src/js/trove/image-lib.js              | 49 ++++++++++++++++++++++++++
 src/js/trove/internal-image-typed.js   |  2 ++
 src/js/trove/internal-image-untyped.js |  2 ++
 src/js/trove/make-image.js             | 14 ++++++++
 4 files changed, 67 insertions(+)

diff --git a/src/js/trove/image-lib.js b/src/js/trove/image-lib.js
index f5677f135..0b6bea3b7 100644
--- a/src/js/trove/image-lib.js
+++ b/src/js/trove/image-lib.js
@@ -1759,6 +1759,52 @@
 
     LineImage.prototype = heir(BaseImage.prototype);
 
+ var verticalSymmetry = function(img) {
+      var width  = img.getWidth();
+      var height = img.getHeight();
+      var halfW  = Math.floor(width / 2);
+      if (halfW === 0 || height === 0) { return 1; }
+      var canvas = makeCanvas(width, height);
+      img.render(canvas.getContext("2d"));
+      var data = canvas.getContext("2d").getImageData(0, 0, width, height).data;
+      var sumSq = 0, count = 0;
+      for (var y = 0; y < height; y++) {
+        for (var x = 0; x < halfW; x++) {
+          var i1 = (y * width + x) * 4;
+          var i2 = (y * width + (width - 1 - x)) * 4;
+          for (var ch = 0; ch < 4; ch++) {
+            var d = data[i1 + ch] - data[i2 + ch];
+            sumSq += d * d;
+          }
+          count += 4;
+        }
+      }
+      return 1 - Math.sqrt(sumSq / count) / 255;
+    };
+
+    var horizontalSymmetry = function(img) {
+      var width  = img.getWidth();
+      var height = img.getHeight();
+      var halfH  = Math.floor(height / 2);
+      if (width === 0 || halfH === 0) { return 1; }
+      var canvas = makeCanvas(width, height);
+      img.render(canvas.getContext("2d"));
+      var data = canvas.getContext("2d").getImageData(0, 0, width, height).data;
+      var sumSq = 0, count = 0;
+      for (var y = 0; y < halfH; y++) {
+        for (var x = 0; x < width; x++) {
+          var i1 = (y * width + x) * 4;
+          var i2 = ((height - 1 - y) * width + x) * 4;
+          for (var ch = 0; ch < 4; ch++) {
+            var d = data[i1 + ch] - data[i2 + ch];
+            sumSq += d * d;
+          }
+          count += 4;
+        }
+      }
+      return 1 - Math.sqrt(sumSq / count) / 255;
+    };
+
     var colorAtPosition = function(img, x, y) {
       var width = img.getWidth(),
       height = img.getHeight(),
@@ -2038,6 +2084,9 @@
         colorBlue: colorBlue,
         colorAlpha: colorAlpha,
         colorString: colorString,
+
+        verticalSymmetry: verticalSymmetry,
+        horizontalSymmetry: horizontalSymmetry,
       }
     );
     return RUNTIME.makeJSModuleReturn();
diff --git a/src/js/trove/internal-image-typed.js b/src/js/trove/internal-image-typed.js
index 84226d468..d8913f546 100644
--- a/src/js/trove/internal-image-typed.js
+++ b/src/js/trove/internal-image-typed.js
@@ -156,6 +156,8 @@
       "image-baseline": ["arrow", ["Image"], "Number"],
       "image-pinhole-x": ["arrow", ["Image"], "Number"],
       "image-pinhole-y": ["arrow", ["Image"], "Number"],
+      "vertical-symmetry": ["arrow", ["Image"], "Number"],
+      "horizontal-symmetry": ["arrow", ["Image"], "Number"],
       "name-to-color": ["arrow", ["String"], "OptColor"],
       "color-named": ["arrow", ["String"], "Color"],
       "empty-image": "Image"
diff --git a/src/js/trove/internal-image-untyped.js b/src/js/trove/internal-image-untyped.js
index 8103ca5c9..3ccabe227 100644
--- a/src/js/trove/internal-image-untyped.js
+++ b/src/js/trove/internal-image-untyped.js
@@ -146,6 +146,8 @@
       "image-baseline": ["arrow", ["Image"], "Number"],
       "image-pinhole-x": ["arrow", ["Image"], "Number"],
       "image-pinhole-y": ["arrow", ["Image"], "Number"],
+      "vertical-symmetry": ["arrow", ["Image"], "Number"],
+      "horizontal-symmetry": ["arrow", ["Image"], "Number"],
       "name-to-color": ["arrow", ["String"], "OptColor"],
       "color-named": ["arrow", ["String"], "Color"],
       "empty-image": "Image"
diff --git a/src/js/trove/make-image.js b/src/js/trove/make-image.js
index 3ed32b12e..957637d0c 100644
--- a/src/js/trove/make-image.js
+++ b/src/js/trove/make-image.js
@@ -1273,6 +1273,20 @@
         return runtime.wrap(img.getHeight());
       });
 
+      f("vertical-symmetry", function(maybeImg) {
+        checkArity(1, arguments, "vertical-symmetry", false);
+        c1("vertical-symmetry", maybeImg, annImage);
+        var img = unwrapImage(maybeImg);
+        return runtime.wrap(image.verticalSymmetry(img));
+      });
+
+      f("horizontal-symmetry", function(maybeImg) {
+        checkArity(1, arguments, "horizontal-symmetry", false);
+        c1("horizontal-symmetry", maybeImg, annImage);
+        var img = unwrapImage(maybeImg);
+        return runtime.wrap(image.horizontalSymmetry(img));
+      });
+
       f("image-baseline", function(maybeImg) {
         checkArity(1, arguments, "image-baseline", false);
         c1("image-baseline", maybeImg, annImage);

From df7657cb8e1e1cb801e20f27d77ad1b54b8686fa Mon Sep 17 00:00:00 2001
From: Emmanuel Schanzer <schanzer@ccs.neu.edu>
Date: Fri, 27 Mar 2026 13:09:04 -0500
Subject: [PATCH 5/9] rename primitives

---
 src/js/trove/internal-image-typed.js   |  4 +--
 src/js/trove/internal-image-untyped.js |  4 +--
 src/js/trove/make-image.js             | 12 +++----
 tests/pyret/tests/test-images.arr      | 47 ++++++++++++++++++++++++++
 4 files changed, 57 insertions(+), 10 deletions(-)

diff --git a/src/js/trove/internal-image-typed.js b/src/js/trove/internal-image-typed.js
index d8913f546..8c8dcf707 100644
--- a/src/js/trove/internal-image-typed.js
+++ b/src/js/trove/internal-image-typed.js
@@ -156,8 +156,8 @@
       "image-baseline": ["arrow", ["Image"], "Number"],
       "image-pinhole-x": ["arrow", ["Image"], "Number"],
       "image-pinhole-y": ["arrow", ["Image"], "Number"],
-      "vertical-symmetry": ["arrow", ["Image"], "Number"],
-      "horizontal-symmetry": ["arrow", ["Image"], "Number"],
+      "image-vertical-symmetry": ["arrow", ["Image"], "Number"],
+      "image-horizontal-symmetry": ["arrow", ["Image"], "Number"],
       "name-to-color": ["arrow", ["String"], "OptColor"],
       "color-named": ["arrow", ["String"], "Color"],
       "empty-image": "Image"
diff --git a/src/js/trove/internal-image-untyped.js b/src/js/trove/internal-image-untyped.js
index 3ccabe227..27e1cd4dd 100644
--- a/src/js/trove/internal-image-untyped.js
+++ b/src/js/trove/internal-image-untyped.js
@@ -146,8 +146,8 @@
       "image-baseline": ["arrow", ["Image"], "Number"],
       "image-pinhole-x": ["arrow", ["Image"], "Number"],
       "image-pinhole-y": ["arrow", ["Image"], "Number"],
-      "vertical-symmetry": ["arrow", ["Image"], "Number"],
-      "horizontal-symmetry": ["arrow", ["Image"], "Number"],
+      "image-vertical-symmetry": ["arrow", ["Image"], "Number"],
+      "image-horizontal-symmetry": ["arrow", ["Image"], "Number"],
       "name-to-color": ["arrow", ["String"], "OptColor"],
       "color-named": ["arrow", ["String"], "Color"],
       "empty-image": "Image"
diff --git a/src/js/trove/make-image.js b/src/js/trove/make-image.js
index 957637d0c..e30a78504 100644
--- a/src/js/trove/make-image.js
+++ b/src/js/trove/make-image.js
@@ -1273,16 +1273,16 @@
         return runtime.wrap(img.getHeight());
       });
 
-      f("vertical-symmetry", function(maybeImg) {
-        checkArity(1, arguments, "vertical-symmetry", false);
-        c1("vertical-symmetry", maybeImg, annImage);
+      f("image-vertical-symmetry", function(maybeImg) {
+        checkArity(1, arguments, "image-vertical-symmetry", false);
+        c1("image-vertical-symmetry", maybeImg, annImage);
         var img = unwrapImage(maybeImg);
         return runtime.wrap(image.verticalSymmetry(img));
       });
 
-      f("horizontal-symmetry", function(maybeImg) {
-        checkArity(1, arguments, "horizontal-symmetry", false);
-        c1("horizontal-symmetry", maybeImg, annImage);
+      f("image-horizontal-symmetry", function(maybeImg) {
+        checkArity(1, arguments, "image-horizontal-symmetry", false);
+        c1("image-horizontal-symmetry", maybeImg, annImage);
         var img = unwrapImage(maybeImg);
         return runtime.wrap(image.horizontalSymmetry(img));
       });
diff --git a/tests/pyret/tests/test-images.arr b/tests/pyret/tests/test-images.arr
index 63c1d8b84..934e0441e 100644
--- a/tests/pyret/tests/test-images.arr
+++ b/tests/pyret/tests/test-images.arr
@@ -253,3 +253,50 @@ logo2 = image-file("pyret-logo-copy.png")
 check:
   logo is logo2
 end
+
+check "Symmetry":
+  fun less-than(n1, n2): n1 < n2 end
+
+  # A simple square should be perfectly symmetrical in both directions
+  perfect-sym = square(50, mode-solid, blue)
+  vertical-symmetry(perfect-sym) is%(within-abs(0.01)) 1
+  horizontal-symmetry(perfect-sym) is%(within-abs(0.01)) 1
+
+  # Two different-colored shapes beside each other break vertical symmetry (left vs right)
+  # but maintain horizontal symmetry (top vs bottom)
+  asym-vert = beside(square(20, mode-solid, red), square(20, mode-solid, blue))
+  vertical-symmetry(asym-vert) is%(less-than) 1
+  horizontal-symmetry(asym-vert) is%(within-abs(0.01)) 1
+
+  # Two different-colored shapes above each other break horizontal symmetry (top vs bottom)
+  # but maintain vertical symmetry (left vs right)
+  asym-horiz = above(square(20, mode-solid, red), square(20, mode-solid, blue))
+  vertical-symmetry(asym-horiz) is%(within-abs(0.01)) 1
+  horizontal-symmetry(asym-horiz) is%(less-than) 1
+
+  # A right triangle is typically asymmetrical in both dimensions
+  rt = right-triangle(40, 50, mode-solid, black)
+  (vertical-symmetry(rt) < 1) is%(within-abs(0.01)) true
+  (horizontal-symmetry(rt) < 1) is%(within-abs(0.01)) true
+
+  # Empty scenes should be perfectly symmetrical
+  empty-sn = empty-scene(50, 50)
+  vertical-symmetry(empty-sn) is%(within-abs(0.01)) 1
+  horizontal-symmetry(empty-sn) is%(within-abs(0.01)) 1
+
+  # Truly empty/0-width or 0-height images should also be symmetrical
+  empty-width = rectangle(0, 100, mode-solid, black)
+  vertical-symmetry(empty-width) is%(within-abs(0.01)) 1
+  horizontal-symmetry(empty-width) is%(within-abs(0.01)) 1
+
+  # Create an asymmetrical image to test cropping
+  asym-base = beside(square(40, mode-solid, red), square(40, mode-solid, blue))
+  vertical-symmetry(asym-base) is%(less-than) 1
+  horizontal-symmetry(asym-base) is%(within-abs(0.01)) 1
+
+  # Cropping just the left side (the red square) restores vertical symmetry
+  cropped-sym = crop(0, 0, 40, 40, asym-base)
+  vertical-symmetry(cropped-sym) is%(within-abs(0.01)) 1
+  horizontal-symmetry(cropped-sym) is%(within-abs(0.01)) 1
+end
+

From 912d8a679bed23c8977991f062b6b12426fc6677 Mon Sep 17 00:00:00 2001
From: Emmanuel Schanzer <schanzer@ccs.neu.edu>
Date: Fri, 27 Mar 2026 13:20:33 -0500
Subject: [PATCH 6/9] fix function names for test suite

---
 tests/pyret/tests/test-images.arr | 32 +++++++++++++++----------------
 1 file changed, 16 insertions(+), 16 deletions(-)

diff --git a/tests/pyret/tests/test-images.arr b/tests/pyret/tests/test-images.arr
index 934e0441e..14321504f 100644
--- a/tests/pyret/tests/test-images.arr
+++ b/tests/pyret/tests/test-images.arr
@@ -259,44 +259,44 @@ check "Symmetry":
 
   # A simple square should be perfectly symmetrical in both directions
   perfect-sym = square(50, mode-solid, blue)
-  vertical-symmetry(perfect-sym) is%(within-abs(0.01)) 1
-  horizontal-symmetry(perfect-sym) is%(within-abs(0.01)) 1
+  image-vertical-symmetry(perfect-sym) is%(within-abs(0.01)) 1
+  image-horizontal-symmetry(perfect-sym) is%(within-abs(0.01)) 1
 
   # Two different-colored shapes beside each other break vertical symmetry (left vs right)
   # but maintain horizontal symmetry (top vs bottom)
   asym-vert = beside(square(20, mode-solid, red), square(20, mode-solid, blue))
-  vertical-symmetry(asym-vert) is%(less-than) 1
-  horizontal-symmetry(asym-vert) is%(within-abs(0.01)) 1
+  image-vertical-symmetry(asym-vert) is%(less-than) 1
+  image-horizontal-symmetry(asym-vert) is%(within-abs(0.01)) 1
 
   # Two different-colored shapes above each other break horizontal symmetry (top vs bottom)
   # but maintain vertical symmetry (left vs right)
   asym-horiz = above(square(20, mode-solid, red), square(20, mode-solid, blue))
-  vertical-symmetry(asym-horiz) is%(within-abs(0.01)) 1
-  horizontal-symmetry(asym-horiz) is%(less-than) 1
+  image-vertical-symmetry(asym-horiz) is%(within-abs(0.01)) 1
+  image-horizontal-symmetry(asym-horiz) is%(less-than) 1
 
   # A right triangle is typically asymmetrical in both dimensions
   rt = right-triangle(40, 50, mode-solid, black)
-  (vertical-symmetry(rt) < 1) is%(within-abs(0.01)) true
-  (horizontal-symmetry(rt) < 1) is%(within-abs(0.01)) true
+  (image-vertical-symmetry(rt) < 1) is%(within-abs(0.01)) true
+  (image-horizontal-symmetry(rt) < 1) is%(within-abs(0.01)) true
 
   # Empty scenes should be perfectly symmetrical
   empty-sn = empty-scene(50, 50)
-  vertical-symmetry(empty-sn) is%(within-abs(0.01)) 1
-  horizontal-symmetry(empty-sn) is%(within-abs(0.01)) 1
+  image-vertical-symmetry(empty-sn) is%(within-abs(0.01)) 1
+  image-horizontal-symmetry(empty-sn) is%(within-abs(0.01)) 1
 
   # Truly empty/0-width or 0-height images should also be symmetrical
   empty-width = rectangle(0, 100, mode-solid, black)
-  vertical-symmetry(empty-width) is%(within-abs(0.01)) 1
-  horizontal-symmetry(empty-width) is%(within-abs(0.01)) 1
+  image-vertical-symmetry(empty-width) is%(within-abs(0.01)) 1
+  image-horizontal-symmetry(empty-width) is%(within-abs(0.01)) 1
 
   # Create an asymmetrical image to test cropping
   asym-base = beside(square(40, mode-solid, red), square(40, mode-solid, blue))
-  vertical-symmetry(asym-base) is%(less-than) 1
-  horizontal-symmetry(asym-base) is%(within-abs(0.01)) 1
+  image-vertical-symmetry(asym-base) is%(less-than) 1
+  image-horizontal-symmetry(asym-base) is%(within-abs(0.01)) 1
 
   # Cropping just the left side (the red square) restores vertical symmetry
   cropped-sym = crop(0, 0, 40, 40, asym-base)
-  vertical-symmetry(cropped-sym) is%(within-abs(0.01)) 1
-  horizontal-symmetry(cropped-sym) is%(within-abs(0.01)) 1
+  image-vertical-symmetry(cropped-sym) is%(within-abs(0.01)) 1
+  image-horizontal-symmetry(cropped-sym) is%(within-abs(0.01)) 1
 end
 

From a8e058dfff1acc6e7b15033aa00ee7500db41c3d Mon Sep 17 00:00:00 2001
From: Emmanuel Schanzer <schanzer@ccs.neu.edu>
Date: Fri, 27 Mar 2026 15:29:37 -0500
Subject: [PATCH 7/9] integrate improvements from @blerner

---
 src/js/trove/image-lib.js | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/src/js/trove/image-lib.js b/src/js/trove/image-lib.js
index 0b6bea3b7..c999436ed 100644
--- a/src/js/trove/image-lib.js
+++ b/src/js/trove/image-lib.js
@@ -1768,10 +1768,12 @@
       img.render(canvas.getContext("2d"));
       var data = canvas.getContext("2d").getImageData(0, 0, width, height).data;
       var sumSq = 0, count = 0;
+
+      const basePixelIndex = (x, y) => ((y * width) + x) * 4;
       for (var y = 0; y < height; y++) {
         for (var x = 0; x < halfW; x++) {
-          var i1 = (y * width + x) * 4;
-          var i2 = (y * width + (width - 1 - x)) * 4;
+          var i1 = basePixelIndex(x, y);
+          var i2 = basePixelIndex(width - 1 - x, y);
           for (var ch = 0; ch < 4; ch++) {
             var d = data[i1 + ch] - data[i2 + ch];
             sumSq += d * d;
@@ -1791,10 +1793,11 @@
       img.render(canvas.getContext("2d"));
       var data = canvas.getContext("2d").getImageData(0, 0, width, height).data;
       var sumSq = 0, count = 0;
+      const basePixelIndex = (x, y) => ((y * width) + x) * 4;
       for (var y = 0; y < halfH; y++) {
         for (var x = 0; x < width; x++) {
-          var i1 = (y * width + x) * 4;
-          var i2 = ((height - 1 - y) * width + x) * 4;
+          var i1 = basePixelIndex(x, y);
+          var i2 = basePixelIndex(x, height - 1 - y);
           for (var ch = 0; ch < 4; ch++) {
             var d = data[i1 + ch] - data[i2 + ch];
             sumSq += d * d;

From 616f18c3d02272b212e182bd16a1fc3613988849 Mon Sep 17 00:00:00 2001
From: Emmanuel Schanzer <schanzer@ccs.neu.edu>
Date: Sat, 28 Mar 2026 08:36:12 -0500
Subject: [PATCH 8/9] attempting to implement @blerner s suggestion

---
 src/arr/trove/internal-image-shared.arr |  2 ++
 src/js/trove/image-lib.js               | 10 ++++++--
 src/js/trove/internal-image-typed.js    |  6 +++++
 src/js/trove/internal-image-untyped.js  |  6 +++++
 src/js/trove/make-image.js              | 32 +++++++++++++++---------
 tests/pyret/tests/test-images.arr       | 33 +++++++++++++------------
 6 files changed, 59 insertions(+), 30 deletions(-)

diff --git a/src/arr/trove/internal-image-shared.arr b/src/arr/trove/internal-image-shared.arr
index f27effa16..5a5ec5046 100644
--- a/src/arr/trove/internal-image-shared.arr
+++ b/src/arr/trove/internal-image-shared.arr
@@ -35,3 +35,5 @@ data FontFamily:
 end
 data FontStyle: fs-normal | fs-italic | fs-slant end
 data FontWeight: fw-normal | fw-bold | fw-light end
+
+data ImageSimilarity: ism-rmse(fudge-factor ::  Number) end
diff --git a/src/js/trove/image-lib.js b/src/js/trove/image-lib.js
index c999436ed..8e2cb4f99 100644
--- a/src/js/trove/image-lib.js
+++ b/src/js/trove/image-lib.js
@@ -1759,7 +1759,13 @@
 
     LineImage.prototype = heir(BaseImage.prototype);
 
- var verticalSymmetry = function(img) {
+   // Note(Emmanuel): As of fall2026 the similarity arg is unused.
+   // We use RMSE across all pixel channels and assume an axis
+   // that is straight down the middle.
+   // But in the future, we could add other forms of similarity
+   // or allow for a "fudge factor" that considers an axis that
+   // isn't *quite* at the middle (imagefluency.com/reference/img_symmetry.html)
+   var verticalSymmetry = function(img, similarity) {
       var width  = img.getWidth();
       var height = img.getHeight();
       var halfW  = Math.floor(width / 2);
@@ -1784,7 +1790,7 @@
       return 1 - Math.sqrt(sumSq / count) / 255;
     };
 
-    var horizontalSymmetry = function(img) {
+    var horizontalSymmetry = function(img, similarity) {
       var width  = img.getWidth();
       var height = img.getHeight();
       var halfH  = Math.floor(height / 2);
diff --git a/src/js/trove/internal-image-typed.js b/src/js/trove/internal-image-typed.js
index 8c8dcf707..79d57dfcc 100644
--- a/src/js/trove/internal-image-typed.js
+++ b/src/js/trove/internal-image-typed.js
@@ -283,6 +283,12 @@
           "fw-light": function(_) { return "light"; },
         });
       },
+      annImageSimilarity: image.ImageSimilarity,
+      unwrapImageSimilarity: function(ism){
+        return runtime.ffi.cases(pyAlwaysTrue, "ImageSimilarity", ism, {
+          "ism-rmse": function(_) { return "ism-rmse"; },
+        });
+      },
       annPlaceX: image.annXPlace,
       unwrapPlaceX: function(px) {
         return runtime.ffi.cases(pyAlwaysTrue, "XPlace", px, {
diff --git a/src/js/trove/internal-image-untyped.js b/src/js/trove/internal-image-untyped.js
index 27e1cd4dd..5dd818804 100644
--- a/src/js/trove/internal-image-untyped.js
+++ b/src/js/trove/internal-image-untyped.js
@@ -305,6 +305,12 @@
           || (x === false);		// false is also acceptable
       }),
       unwrapFontWeight: identity,
+      annImageSimilarity: ann("Image Similarity", function(x){
+        return (isString(x) &&
+                (x.toString().toLowerCase() == "ism-rmse" ||
+                 false)) // add other similarity measure here
+      }),
+      unwrapImageSimilarity: identity,
       annPlaceX: ann("X Place (\"left\", \"middle\", \"center\", \"pinhole\", or \"right\")", isPlaceX),
       unwrapPlaceX: function(val) {
         if (val.toString().toLowerCase() == "center") return "middle";
diff --git a/src/js/trove/make-image.js b/src/js/trove/make-image.js
index e30a78504..ab31bb6c4 100644
--- a/src/js/trove/make-image.js
+++ b/src/js/trove/make-image.js
@@ -41,6 +41,8 @@
       const unwrapFontStyle = annots.unwrapFontStyle;
       const annFontWeight = annots.annFontWeight;
       const unwrapFontWeight = annots.unwrapFontWeight;
+      const annImageSimilarity = annots.annImageSimilarity;
+      const unwrapImageSimilarity = annots.unwrapImageSimilarity;
       const annPlaceX = annots.annPlaceX;
       const unwrapPlaceX = annots.unwrapPlaceX;
       const annPlaceY = annots.annPlaceY;
@@ -1273,18 +1275,24 @@
         return runtime.wrap(img.getHeight());
       });
 
-      f("image-vertical-symmetry", function(maybeImg) {
-        checkArity(1, arguments, "image-vertical-symmetry", false);
-        c1("image-vertical-symmetry", maybeImg, annImage);
-        var img = unwrapImage(maybeImg);
-        return runtime.wrap(image.verticalSymmetry(img));
-      });
-
-      f("image-horizontal-symmetry", function(maybeImg) {
-        checkArity(1, arguments, "image-horizontal-symmetry", false);
-        c1("image-horizontal-symmetry", maybeImg, annImage);
-        var img = unwrapImage(maybeImg);
-        return runtime.wrap(image.horizontalSymmetry(img));
+      f("image-vertical-symmetry", function(maybeImg, maybeSimilarityMeasure) {
+        checkArity(2, arguments, "image-vertical-symmetry", false);
+         c2("image-vertical-symmetry",
+           maybeImg, annImage,
+           maybeSimilarityMeasure, annImageSimilarity);
+        var img        = unwrapImage(maybeImg);
+        var similarity = unwrapImageSimilarity(annImageSimilarity);
+        return runtime.wrap(image.verticalSymmetry(img, similarity));
+      });
+
+      f("image-horizontal-symmetry", function(maybeImg, maybeSimilarityMeasure) {
+        checkArity(2, arguments, "image-horizontal-symmetry", false);
+         c2("image-horizontal-symmetry",
+           maybeImg, annImage,
+           maybeSimilarityMeasure, annImageSimilarity);
+        var img        = unwrapImage(maybeImg);
+        var similarity = unwrapImageSimilarity(annImageSimilarity);
+        return runtime.wrap(image.horizontalSymmetry(img, similarity));
       });
 
       f("image-baseline", function(maybeImg) {
diff --git a/tests/pyret/tests/test-images.arr b/tests/pyret/tests/test-images.arr
index 14321504f..88157f90b 100644
--- a/tests/pyret/tests/test-images.arr
+++ b/tests/pyret/tests/test-images.arr
@@ -257,46 +257,47 @@ end
 check "Symmetry":
   fun less-than(n1, n2): n1 < n2 end
 
+
   # A simple square should be perfectly symmetrical in both directions
   perfect-sym = square(50, mode-solid, blue)
-  image-vertical-symmetry(perfect-sym) is%(within-abs(0.01)) 1
-  image-horizontal-symmetry(perfect-sym) is%(within-abs(0.01)) 1
+  image-vertical-symmetry(perfect-sym, ism-rmse(0)) is%(within-abs(0.01)) 1
+  image-horizontal-symmetry(perfect-sym, ism-rmse(0)) is%(within-abs(0.01)) 1
 
   # Two different-colored shapes beside each other break vertical symmetry (left vs right)
   # but maintain horizontal symmetry (top vs bottom)
   asym-vert = beside(square(20, mode-solid, red), square(20, mode-solid, blue))
-  image-vertical-symmetry(asym-vert) is%(less-than) 1
-  image-horizontal-symmetry(asym-vert) is%(within-abs(0.01)) 1
+  image-vertical-symmetry(asym-vert, ism-rmse(0)) is%(less-than) 1
+  image-horizontal-symmetry(asym-vert, ism-rmse(0)) is%(within-abs(0.01)) 1
 
   # Two different-colored shapes above each other break horizontal symmetry (top vs bottom)
   # but maintain vertical symmetry (left vs right)
   asym-horiz = above(square(20, mode-solid, red), square(20, mode-solid, blue))
-  image-vertical-symmetry(asym-horiz) is%(within-abs(0.01)) 1
-  image-horizontal-symmetry(asym-horiz) is%(less-than) 1
+  image-vertical-symmetry(asym-horiz, ism-rmse(0)) is%(within-abs(0.01)) 1
+  image-horizontal-symmetry(asym-horiz, ism-rmse(0)) is%(less-than) 1
 
   # A right triangle is typically asymmetrical in both dimensions
   rt = right-triangle(40, 50, mode-solid, black)
-  (image-vertical-symmetry(rt) < 1) is%(within-abs(0.01)) true
-  (image-horizontal-symmetry(rt) < 1) is%(within-abs(0.01)) true
+  (image-vertical-symmetry(rt, ism-rmse(0)) < 1) is%(within-abs(0.01)) true
+  (image-horizontal-symmetry(rt, ism-rmse(0)) < 1) is%(within-abs(0.01)) true
 
   # Empty scenes should be perfectly symmetrical
   empty-sn = empty-scene(50, 50)
-  image-vertical-symmetry(empty-sn) is%(within-abs(0.01)) 1
-  image-horizontal-symmetry(empty-sn) is%(within-abs(0.01)) 1
+  image-vertical-symmetry(empty-sn, ism-rmse(0)) is%(within-abs(0.01)) 1
+  image-horizontal-symmetry(empty-sn, ism-rmse(0)) is%(within-abs(0.01)) 1
 
   # Truly empty/0-width or 0-height images should also be symmetrical
   empty-width = rectangle(0, 100, mode-solid, black)
-  image-vertical-symmetry(empty-width) is%(within-abs(0.01)) 1
-  image-horizontal-symmetry(empty-width) is%(within-abs(0.01)) 1
+  image-vertical-symmetry(empty-width, ism-rmse(0)) is%(within-abs(0.01)) 1
+  image-horizontal-symmetry(empty-width, ism-rmse(0)) is%(within-abs(0.01)) 1
 
   # Create an asymmetrical image to test cropping
   asym-base = beside(square(40, mode-solid, red), square(40, mode-solid, blue))
-  image-vertical-symmetry(asym-base) is%(less-than) 1
-  image-horizontal-symmetry(asym-base) is%(within-abs(0.01)) 1
+  image-vertical-symmetry(asym-base, ism-rmse(0)) is%(less-than) 1
+  image-horizontal-symmetry(asym-base, ism-rmse(0)) is%(within-abs(0.01)) 1
 
   # Cropping just the left side (the red square) restores vertical symmetry
   cropped-sym = crop(0, 0, 40, 40, asym-base)
-  image-vertical-symmetry(cropped-sym) is%(within-abs(0.01)) 1
-  image-horizontal-symmetry(cropped-sym) is%(within-abs(0.01)) 1
+  image-vertical-symmetry(cropped-sym, ism-rmse(0)) is%(within-abs(0.01)) 1
+  image-horizontal-symmetry(cropped-sym, ism-rmse(0)) is%(within-abs(0.01)) 1
 end
 

From 65d19a835fac78f59fc4639e2da4d26c40fc04e5 Mon Sep 17 00:00:00 2001
From: Emmanuel Schanzer <schanzer@ccs.neu.edu>
Date: Sat, 28 Mar 2026 09:22:55 -0500
Subject: [PATCH 9/9] Emmanuel learns how the annotation system works

---
 src/js/trove/image-lib.js              | 3 +++
 src/js/trove/internal-image-typed.js   | 9 ++++++---
 src/js/trove/internal-image-untyped.js | 7 +++++--
 src/js/trove/make-image.js             | 4 ++--
 4 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/src/js/trove/image-lib.js b/src/js/trove/image-lib.js
index 8e2cb4f99..c86520753 100644
--- a/src/js/trove/image-lib.js
+++ b/src/js/trove/image-lib.js
@@ -23,6 +23,7 @@
     var isPoint = function(p) { return unwrap(rawIsPoint.app(p)); };
     var unwrap = RUNTIME.unwrap;
 
+
     var hasOwnProperty = {}.hasOwnProperty;
 
 
@@ -58,6 +59,7 @@
     var annFontFamily = imageTypes["FontFamily"];
     var annFontStyle = imageTypes["FontStyle"];
     var annFontWeight = imageTypes["FontWeight"];
+    var annImageSimilarity = imageTypes["ImageSimilarity"];
     
     // Color database
     var ColorDb = function() {
@@ -2084,6 +2086,7 @@
         isTextImage: isTextImage,
         isFileImage: isFileImage,
         isFileVideo: isFileVideo,
+        annImageSimilarity: annImageSimilarity,
 
         makeColor: makeColor,
         isColor: isColor,
diff --git a/src/js/trove/internal-image-typed.js b/src/js/trove/internal-image-typed.js
index 79d57dfcc..b083eafe8 100644
--- a/src/js/trove/internal-image-typed.js
+++ b/src/js/trove/internal-image-typed.js
@@ -62,6 +62,9 @@
               [{ tag: "name",
                  origin: { "import-type": "uri", uri: "builtin://internal-image-shared" },
                  name: "Point" }]],
+      "ImageSimilarity": { tag: "name",
+                     origin: { "import-type": "uri", uri: "builtin://internal-image-shared" },
+                     name: "ImageSimilarity" },
     },
     values: {
       "circle": ["arrow", ["Number", "FillMode", "Color"], "Image"],
@@ -156,8 +159,8 @@
       "image-baseline": ["arrow", ["Image"], "Number"],
       "image-pinhole-x": ["arrow", ["Image"], "Number"],
       "image-pinhole-y": ["arrow", ["Image"], "Number"],
-      "image-vertical-symmetry": ["arrow", ["Image"], "Number"],
-      "image-horizontal-symmetry": ["arrow", ["Image"], "Number"],
+      "image-vertical-symmetry": ["arrow", ["Image", "ImageSimilarity"], "Number"],
+      "image-horizontal-symmetry": ["arrow", ["Image", "ImageSimilarity"], "Number"],
       "name-to-color": ["arrow", ["String"], "OptColor"],
       "color-named": ["arrow", ["String"], "Color"],
       "empty-image": "Image"
@@ -283,7 +286,7 @@
           "fw-light": function(_) { return "light"; },
         });
       },
-      annImageSimilarity: image.ImageSimilarity,
+      annImageSimilarity: image.annImageSimilarity,
       unwrapImageSimilarity: function(ism){
         return runtime.ffi.cases(pyAlwaysTrue, "ImageSimilarity", ism, {
           "ism-rmse": function(_) { return "ism-rmse"; },
diff --git a/src/js/trove/internal-image-untyped.js b/src/js/trove/internal-image-untyped.js
index 5dd818804..4e71a33f8 100644
--- a/src/js/trove/internal-image-untyped.js
+++ b/src/js/trove/internal-image-untyped.js
@@ -48,6 +48,9 @@
               [{ tag: "name",
                  origin: { "import-type": "uri", uri: "builtin://internal-image-shared" },
                  name: "Point" }]],
+      "ImageSimilarity": { tag: "name",
+                     origin: { "import-type": "uri", uri: "builtin://internal-image-shared" },
+                     name: "ImageSimilarity" },
     },
     values: {
       "circle": ["arrow", ["Number", "FillMode", "ColorString"], "Image"],
@@ -146,8 +149,8 @@
       "image-baseline": ["arrow", ["Image"], "Number"],
       "image-pinhole-x": ["arrow", ["Image"], "Number"],
       "image-pinhole-y": ["arrow", ["Image"], "Number"],
-      "image-vertical-symmetry": ["arrow", ["Image"], "Number"],
-      "image-horizontal-symmetry": ["arrow", ["Image"], "Number"],
+      "image-vertical-symmetry": ["arrow", ["Image", "ImageSimilarity"], "Number"],
+      "image-horizontal-symmetry": ["arrow", ["Image", "ImageSimilarity"], "Number"],
       "name-to-color": ["arrow", ["String"], "OptColor"],
       "color-named": ["arrow", ["String"], "Color"],
       "empty-image": "Image"
diff --git a/src/js/trove/make-image.js b/src/js/trove/make-image.js
index ab31bb6c4..f72ad12e5 100644
--- a/src/js/trove/make-image.js
+++ b/src/js/trove/make-image.js
@@ -1281,7 +1281,7 @@
            maybeImg, annImage,
            maybeSimilarityMeasure, annImageSimilarity);
         var img        = unwrapImage(maybeImg);
-        var similarity = unwrapImageSimilarity(annImageSimilarity);
+        var similarity = unwrapImageSimilarity(maybeSimilarityMeasure);
         return runtime.wrap(image.verticalSymmetry(img, similarity));
       });
 
@@ -1291,7 +1291,7 @@
            maybeImg, annImage,
            maybeSimilarityMeasure, annImageSimilarity);
         var img        = unwrapImage(maybeImg);
-        var similarity = unwrapImageSimilarity(annImageSimilarity);
+        var similarity = unwrapImageSimilarity(maybeSimilarityMeasure);
         return runtime.wrap(image.horizontalSymmetry(img, similarity));
       });