Boost the contrast of one rectangle in a photo, such as a dark doorway or a washed-out sky, and feather the edge so the patch blends in. Whole-image mode is there too.
Takes the rectangle you define, builds a brightness histogram from only those pixels, and spreads their tones across the full range while leaving the rest of the picture untouched. Because the histogram comes from the patch alone, a dark region gets exactly the lift it needs rather than a compromise chosen for the whole frame. Feather blends the edited pixels back into the original over a border of the width you choose, so the correction reads as light, not as a pasted-on square.
A 6000 × 4000 photo of a church interior where the nave is well exposed but the side chapel on the left is almost black. Set From left 0, From top 900, Width 1800, Height 2600, or start from the Left half chip and shrink it. At 100 percent strength the chapel’s carvings appear but the patch looks lit by a floodlight; 70 percent with a 120 px feather looks like a properly exposed photo. For a washed-out sky use the Top half chip with a 200 px feather so the horizon does not show a line.
This is a local fix for one problem region: a shadowed face, a dark interior seen through a door, a foggy distant hill, a faded corner of a scan. If the whole image is flat, Equalize Image is simpler and its Adaptive mode handles several regions at once. If the region is simply too dark rather than lacking contrast, Change Exposure on a crop may look more natural, and if the region should be hidden rather than revealed, Censor Photo is the tool.
Selected area uses the four pixel fields; Whole image ignores them. The chips jump to halves and the centre, which are good starting points. Feather is the width in pixels of the blend at the rectangle’s edge; it cannot exceed half the shorter side. Strength blends the equalized patch with the original. Output Same keeps the original file type; the file name gets an -equalized suffix unless you change the pattern.
How do I know where the rectangle is? The numbers are in original-image pixels, measured from the top-left corner, and the preview shows the equalized patch live. Use the chips for halves of the picture, then adjust the four fields until the patch covers what you want; hold Space to compare with the original.
Why can I see the edge of the rectangle? The patch has different contrast from its surroundings. Raise Feather so the effect fades out over 40 to 100 pixels, and lower Strength a little; the two together usually make the boundary invisible.
Can I equalize two separate areas? One rectangle per pass. Download the result, drop it back in, and set a second rectangle; the settings are remembered so the second pass is quick.
Is anything uploaded? No. The histogram for the rectangle is calculated in your browser and the pixels are rewritten there; the photo never leaves your device.