Little Toolkit

PNG Transparent Border Cropper

Fit transparent padding to the content with traceable pixels and source-file details.

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

PNG Transparent Border Cropper User Guide

Locally find the exact bounds of nontransparent pixels from original 8-bit PNG alpha data. Only fully transparent outer rows and columns are removed; transparent holes, translucent shadows and every pixel inside the bounds are preserved.

How to use

  1. Import one supported static 8-bit RGB or RGBA PNG.
  2. Check the original and trimmed dimensions, top-left offset, and complete source and output previews on a transparency checkerboard.
  3. Confirm the crop bounds, then save a new copy whose filename ends in _trimmed.png.

Formats and limits

  • One image at a time, up to 12 million pixels (1,200 × 10,000), 20 MiB and 8,192 px per side. Processing runs in a dedicated worker; canceling, replacing the file or leaving the page discards the result.
  • The first version accepts only static 8-bit-per-channel RGB (type 2) or RGBA (type 6) PNGs. Grayscale, grayscale with alpha, indexed color, tRNS, 16-bit, APNG, corrupt and structurally inconsistent files are explicitly rejected.
  • The crop is the smallest rectangle containing every pixel with alpha > 0, with no padding or adjustable threshold. A fully transparent image does not produce a fake 1 × 1 result; dimensions stay unchanged when content already touches all four edges.

Output

The new PNG copy contains only the original RGB/alpha pixels inside the crop rectangle. It is not scaled and does not overwrite the source; metadata, color descriptions and a smaller file size are not guaranteed.

Frequently asked questions

Will a very faint translucent shadow be trimmed?

No. Alpha = 1 / 255 still counts as content. Only outer rows and columns whose alpha is exactly 0 are removed, and transparent holes inside the bounds remain.

Why are some PNG files rejected?

The first version uses a narrow format allowlist so a browser cannot silently reduce bit depth or expand a transparency key while the tool claims exact pixels. Save the image as a nonanimated 8-bit RGB or RGBA PNG, then import it again.

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.