Little Toolkit

PNG Alpha Mask Exporter

Turn PNG transparency into a grayscale mask, keeping the same dimensions and coordinates.

Enable JavaScript for interactive processing. You can read the instructions, limits, and FAQs below without it. Files are processed only in your browser.

PNG Alpha Mask Exporter User Guide

Read one static 8-bit RGBA PNG locally and map every raw alpha value to an opaque grayscale mask. White is opaque and black is transparent; dimensions and coordinates stay unchanged.

How to use

  1. Choose a PNG. The tool checks the original IHDR, complete chunks, checksums and compressed pixel data first.
  2. Compare the source and alpha mask previews. Transparent holes, faint edges and margins keep their coordinates; values 0, 1, 128 and 255 are never thresholded.
  3. Select Download mask PNG to save a new copy. Replacing the file, cancelling, clearing or leaving the page discards the previous result.

Formats and limits

  • Accepts only static RGBA PNGs with original IHDR color type 6 and 8 bits per channel, including noninterlaced and Adam7 files. RGB, grayscale, indexed color, tRNS, 16-bit and all APNG chunks are rejected.
  • Limits: 20 MiB per file, 12 million pixels, 8,192 px per side and 4,096 chunks; output is capped at 64 MiB. These are safety limits, not a performance guarantee for every device.
  • No cropping, resizing, rotation, inversion, background removal or channel packing. Raw IHDR dimensions and sample order are used without EXIF orientation. Browser previews are not precise measurements of raw grayscale values.

Output

Outputs a same-size 8-bit RGBA PNG: R = G = B = source alpha, A = 255. The filename ends in _alpha-mask.png. Text, EXIF, ICC and gamma metadata are removed. The original file is unchanged; all data stays in this page's memory.

Frequently asked questions

Does alpha = 1 become pure black?

No. Alpha 1 becomes RGB (1, 1, 1), alpha 128 becomes (128, 128, 128), and every output alpha is 255. There is no thresholding or luminance conversion.

Why are RGB PNGs rejected?

This tool reads the original alpha channel of RGBA PNGs. RGB files without alpha, palette transparency and tRNS are explicitly rejected rather than guessed or converted.

The file name and content are only processed in your browser and are not transmitted to the server. The original file will not be overwritten. Please export the required results before leaving the tool.