Online Batch Image Grayscale Tool

What this tool actually does

Batch grayscale conversion accepts up to 30 selected images and has no adjustment controls. Generate converts every loaded image independently; selecting files only shows source previews and does not apply the effect automatically.

Checkable behavior

For each pixel the browser calculates weighted luminance Y=(299R+587G+114B)/1000, writes that same value to red, green and blue, and retains the original alpha. Dimensions do not change. This is a fixed luminance transform, not a simple unweighted RGB average.

Controls, output and limitations

Verified primary-color examples: RGB(255,0,0) becomes approximately RGB(76,76,76), RGB(0,255,0) becomes RGB(150,150,150), and RGB(0,0,255) becomes approximately RGB(29,29,29). Green therefore appears lighter than equal-intensity red or blue under the weighting.

The result removes RGB chroma but does not threshold pixels into pure black and white, create a one-bit bitmap, offer channel-mixer weights, add film grain or simulate a named black-and-white film stock. Transparent pixels retain their alpha even though hidden RGB bytes are also converted.

Each input must have an image MIME type, be at most 25 MiB and decode to no more than 24,000,000 pixels. The selected batch is capped at 100 MiB and 40,000,000 decoded pixels; selecting more than 30 files rejects the entire batch.

Generate creates one browser preview per loaded image. Every result is encoded as PNG and named from the source base name plus -grayscale.png. Download all starts separate downloads about 180 ms apart; it does not create a ZIP, retain source format or preserve metadata.

Processing is local in the browser. Review brand colors, charts and accessibility cues before export because color-only distinctions can disappear after conversion. The tool does not analyze contrast compliance, recover detail or preserve editable layers; keep the originals.