Online Image Local Equalization Tool

What Online Image Local Equalization Tool actually does

Expands tonal contrast inside one rectangular region while leaving pixels outside it unchanged. Region controls are percentages of decoded width and height and default to X=10, Y=10, width=80 and height=80. There is no ellipse, feather, histogram display, channel selector, CLAHE tile size or batch mode.

Checkable example

A constant-luminance selection is left unchanged instead of amplifying division by an empty tonal range. Verified grayscale example: a selected region containing only values 50 and 150 maps those pixels to 0 and 255. Colored channels can clip differently because the same luminance-derived endpoints are applied to R, G and B.

Controls, output and limits

The browser scans weighted luminance Y=0.299R+0.587G+0.114B in the selected region to find its minimum and maximum. When max is greater than min, it maps each RGB channel by (channel-minY)*255/(maxY-minY), clamped to 0..255. Alpha and dimensions remain unchanged.

X and Y are clamped to 0..99.999 percent, and positive width and height are constrained to the remaining image area. On a 1000 by 500 source, defaults process the rectangle from x=100 through 899 and y=50 through 449. Changing values does nothing until Generate is pressed again.

One browser-decodable image up to 25 MiB (26 214 400 B) and 24,000,000 pixels is processed locally and exported as PNG at the source dimensions. This is simple regional linear stretching, not full histogram equalization, adaptive contrast, denoising, RAW recovery or color-managed Lab processing; keep the original and inspect color clipping.