Describe the bug
When enabling TRY_HARDER I couldn't get horizontal scanning working. It would only work if the barcode was rotated 90 degrees (portrait). But disabling TRY_HARDER, it would go back to allowing me to scan horizontal barcodes again.
The issue is with HTMLCanvasElementLuminanceSource.toGrayscaleBuffer()
static toGrayscaleBuffer(imageBuffer, width, height, doAutoInvert = false) {
const grayscaleBuffer = new Uint8ClampedArray(width * height);
HTMLCanvasElementLuminanceSource.FRAME_INDEX = !HTMLCanvasElementLuminanceSource.FRAME_INDEX;
if (HTMLCanvasElementLuminanceSource.FRAME_INDEX || !doAutoInvert) {
for (let i = 0, j = 0, length = imageBuffer.length; i < length; i += 4, j++) {
let gray;
const alpha = imageBuffer[i + 3];
// The color of fully-transparent pixels is irrelevant. They are often, technically, fully-transparent
// black (0 alpha, and then 0 RGB). They are often used, of course as the "white" area in a
// barcode image. Force any such pixel to be white:
if (alpha === 0) {
gray = 0xFF;
}
else {
const pixelR = imageBuffer[i];
const pixelG = imageBuffer[i + 1];
const pixelB = imageBuffer[i + 2];
// .299R + 0.587G + 0.114B (YUV/YIQ for PAL and NTSC),
// (306*R) >> 10 is approximately equal to R*0.299, and so on.
// 0x200 >> 10 is 0.5, it implements rounding.
gray = (306 * pixelR +
601 * pixelG +
117 * pixelB +
0x200) >> 10;
}
grayscaleBuffer[j] = gray;
}
}
else {
for (let i = 0, j = 0, length = imageBuffer.length; i < length; i += 4, j++) {
let gray;
const alpha = imageBuffer[i + 3];
// The color of fully-transparent pixels is irrelevant. They are often, technically, fully-transparent
// black (0 alpha, and then 0 RGB). They are often used, of course as the "white" area in a
// barcode image. Force any such pixel to be white:
if (alpha === 0) {
gray = 0xFF;
}
else {
const pixelR = imageBuffer[i];
const pixelG = imageBuffer[i + 1];
const pixelB = imageBuffer[i + 2];
// .299R + 0.587G + 0.114B (YUV/YIQ for PAL and NTSC),
// (306*R) >> 10 is approximately equal to R*0.299, and so on.
// 0x200 >> 10 is 0.5, it implements rounding.
gray = (306 * pixelR +
601 * pixelG +
117 * pixelB +
0x200) >> 10;
}
grayscaleBuffer[j] = 0xFF - gray;
}
}
return grayscaleBuffer;
}
Which has the following line
HTMLCanvasElementLuminanceSource.FRAME_INDEX = !HTMLCanvasElementLuminanceSource.FRAME_INDEX;
Which makes the canvas capture invert every other frame ..
The issue is. If you enable TRY_HARDER, it does a second pass with a second decode. So the first try will be inverted, and the second try (by the TRY_HARDER flag) will not be inverted. This means the initial "normal" pass will always fail (as inverted), and the second rotated attempt by TRY_HARDER will always pass.
To Reproduce
Enable TRY_HARDER on a HTMLCanvasElement implementation
Describe the bug
When enabling TRY_HARDER I couldn't get horizontal scanning working. It would only work if the barcode was rotated 90 degrees (portrait). But disabling TRY_HARDER, it would go back to allowing me to scan horizontal barcodes again.
The issue is with
HTMLCanvasElementLuminanceSource.toGrayscaleBuffer()Which has the following line
Which makes the canvas capture invert every other frame ..
The issue is. If you enable TRY_HARDER, it does a second pass with a second decode. So the first try will be inverted, and the second try (by the TRY_HARDER flag) will not be inverted. This means the initial "normal" pass will always fail (as inverted), and the second rotated attempt by TRY_HARDER will always pass.
To Reproduce
Enable TRY_HARDER on a HTMLCanvasElement implementation