PNGMender

Signature · chunks · CRC · hex

PNG chunk inspector

See exactly what is inside a PNG: every chunk with its offset, length and checksum, decoded into plain language, with warnings for anything out of spec.

Parsed in this tab. Nothing is uploaded.

Drop a PNG to inspect

Any PNG or APNG, even a damaged one.

How to read a PNG

A PNG file is an 8-byte signature followed by chunks. Each chunk has a 4-byte length, a 4-letter type, its data and a CRC-32 checksum of the type and data. The inspector walks them in order, recomputes every checksum and decodes the fields it knows.

The case of each letter in a chunk type means something. An uppercase first letter marks a critical chunk (IHDR, PLTE, IDAT, IEND) that a decoder must understand; lowercase marks an ancillary one that it may skip. A lowercase second letter marks a private chunk, and a lowercase fourth letter says editors may copy it into a modified file.

Select any chunk type in the table to see its fields and its raw bytes. The hex view shows the length, type, data and CRC exactly as stored.

What the warnings catch

  • CRC mismatches, truncated chunks and a missing IEND (a cut-off download).
  • Chunks in the wrong order, such as gAMA after the image data, or duplicates of chunks that may appear once.
  • Invalid lengths, bit depths, palette sizes and transparency data.
  • Extra bytes after IEND, which sometimes hide a ZIP archive.
  • APNG frame counts and sequence numbers that do not add up.
  • Apple's iOS-optimised CgBI PNGs, which most software cannot open.

Found damage? The Repair PNG tool fixes what can be fixed, and the metadata remover strips text and EXIF chunks.

Questions

What does a CRC mismatch mean?

The checksum stored after a chunk does not match its type and data, so either the data or the checksum was damaged, usually by a bad download, disk error or careless editing tool. Strict decoders reject the file. If the image still decodes, the checksum was probably the damaged part.

Which chunks can I safely delete?

Text (tEXt, zTXt, iTXt), time (tIME), EXIF (eXIf) and most private chunks never change how the image looks. Colour chunks (iCCP, sRGB, gAMA, cHRM) can change how colours are shown, and tRNS, PLTE, IDAT and the APNG chunks are part of the picture itself.

Why is having both sRGB and iCCP a warning?

The PNG specification says a file should carry only one of them. Decoders that support colour management use the ICC profile and ignore sRGB, so the extra chunk is at best wasted bytes and at worst a contradiction.

How is DPI stored in a PNG?

In the pHYs chunk, as pixels per metre. The inspector converts it to dots per inch: 2835 pixels per metre is 72 DPI and 11811 is 300 DPI. Screens ignore it; print and layout software use it to choose a default size.

Is my file uploaded?

No. The file is read and parsed in a background worker in this browser tab; compressed text is decompressed with the browser's built-in DecompressionStream. Nothing is sent anywhere.

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