Image Histogram

The image is decoded into an off-screen <canvas> and read back with getImageData. To keep memory bounded, the library samples at most one megapixel of the original image (every N-th pixel across the buffer); the per-channel statistics are still representative at that scale for any natural image.

The luminance channel is the Rec.709 integer-weighted brightness: Y = round((54·R + 183·G + 19·B) / 256). The near-black / near-white shares use the 0–8 / 247–255 thresholds (typical "almost pure" cut-offs in print and screen pipelines).