Batch Image Levels — Black and White Points
Set shared black and white points for up to 30 images, stretch RGB levels locally and download PNGs at the original dimensions.
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What this tool actually does
Use the two numeric fields; there are no sliders. Only calculation values are changed: shadow is limited to 0–254, and highlight to shadow+1…255. A highlight of 0 or an empty field uses 255 first. Thus 100/50 uses 100/101, but 100/0 uses 100/255. The fields are not rewritten. Each generation starts from the loaded sources; 0/255 restores their decoded RGB.
Checkable behavior
Every red, green and blue channel is mapped independently by output=(channel-shadow)*255/(highlight-shadow), then clamped and byte-rounded. Values at or below shadow become 0 and values at or above highlight become 255. Alpha and image dimensions remain unchanged.
Controls, output and limitations
Verified defaults: with shadow 20 and highlight 235, RGB(20,128,235) becomes RGB(0,128,255), while RGB(0,100,255) becomes approximately RGB(0,95,255). With the full 0..255 range RGB is unchanged.
Worked batch use: load several product images from the same lighting setup, keep 20/235 and Generate. The shared mapping deepens shadows and raises highlights in all files, but images with different exposure can lose different details. Review each preview rather than treating the batch as automatic correction.
Each input must have an image MIME type, be at most 25 MiB and decode to at most 24,000,000 pixels. The selected batch is capped at 100 MiB and 40,000,000 decoded pixels, and selecting more than 30 files rejects the whole batch.
Every result is encoded as PNG and named from its source base name plus -clip.png. Download all starts separate downloads about 180 ms apart; it does not create a ZIP, preserve the original format or offer an output-format selector.
Processing is local in the browser and Generate must be pressed after changing the levels. This tool is not geometric cropping, sharpening, RAW exposure recovery, adaptive contrast, an eyedropper, histogram auto-levels or selective masking. Narrow ranges permanently collapse tonal distinctions in the exported copy, so retain the originals.
Processing takes place locally in your browser.