Add or subtract up to 255 from the red, green and blue of every pixel. Tint shadows, cool a scene, lift or darken evenly, or isolate a single channel.
Adds the number you set to the red, green or blue value of every pixel and clips the result to the 0 to 255 range. Unlike a percentage gain, an offset moves the darkest and the brightest pixels by the same amount, so +30 blue turns pure black into a deep navy while leaving a bright white sky white, because white is already at the top of the range. That behaviour is what makes offsets the right tool for colouring shadows and for the split-tone looks where shadows go cool and highlights stay neutral.
A 3000 × 2000 street photo at dusk with muddy grey shadows: red −12, green 0, blue +22 gives the shadows a clean cool blue while the shop lights, already near 255 in red, stay warm. The same photo with all three at +20 lifts the whole exposure evenly, the equivalent of a mild brightness boost. Subtracting 255 from green and blue turns the picture into a pure red-channel image, handy for checking where a photo’s detail actually lives.
Use it for shadow tints, split-tone grades, quick even lifts and channel isolation. For fixing a colour cast, Adjust Color Channels is usually better, since a cast lives in the highlights and a multiplication scales with brightness. To recolour without changing how light or dark anything is, Adjust HSL is the tool. For a two-colour poster look with full control over the shadow and highlight colours, use Duotone Effect rather than pushing offsets to their limits.
The three offset sliders run from −255 to +255 in single steps; the panel summary shows the triplet. Warm shadows and Cool shadows move red and blue by 18 in opposite directions, Lift and Darken move all three together by 20, and the Only chips remove the other two channels completely. Reset returns to zero. Output Same keeps the original file type; choose PNG if you are producing channel splits for later work.
Why does raising red also make the black areas reddish? Because an offset is added to every pixel, including those that were 0. That is the defining difference from Adjust Color Channels, which multiplies and therefore leaves black alone. Use the offset when you want the tint in the shadows, and the gain when you do not.
How much is too much? For a colour grade, keep each offset within about ±40. Beyond ±60 large parts of the picture hit 0 or 255 in that channel and detail flattens. Full ±255 is only useful for isolating a single channel or making a deliberately graphic result.
Can I use this to split an image into its R, G and B channels? Yes. The Only red, Only green and Only blue chips subtract 255 from the other two channels, leaving one channel's data shown in its own colour. Save each one as PNG. Grayscale Image with the Red filter gives a neutral view of a single channel instead.
Are the photos uploaded? No. The arithmetic runs on your device in the browser, and the page keeps working with the network off.