pngcheck verifies the integrity of PNG, JNG and MNG files (by checking the internal 32-bit CRCs [checksums] and decompressing the image data); it can optionally dump almost all of the chunk-level information in the image in human-readable form. For example, it can be used to print the basic statistics about an image (dimensions, bit depth, etc.); to list the color and transparency info in its palette (assuming it has one); or to extract the embedded text annotations. This is a command-line program with batch capabilities.

Here's some sample output (screen shots, eh?):

    % pngcheck -vt ArcTriomphe-iCCP-red-blue-swap.png
    File: ArcTriomphe-iCCP-red-blue-swap.png (5171 bytes)
      chunk IHDR at offset 0x0000c, length 13
        64 x 64 image, 8-bit colormap, non-interlaced
      chunk iCCP at offset 0x00025, length 461
        profile name = Swapped red & blue channel
        compression method = 0 (deflate), compressed profile = 433 bytes
      chunk PLTE at offset 0x001fe, length 759: 253 palette entries
      chunk IDAT at offset 0x00501, length 3616
        zlib: deflated, 32K window, default compression
      chunk tEXt at offset 0x0132d, length 68, keyword: Title
        PNG color-correction test image, swapped red and blue channels
      chunk tEXt at offset 0x0137d, length 143, keyword: Copyright
        Copyright 2005 Greg Roelofs. Licensed under Creative Commons
        AttributionNonCommercial, http://creativecommons.org/licenses/by-nc/2.5/
      chunk tIME at offset 0x01418, length 7: 16 Aug 2005 07:07:07 GMT
      chunk IEND at offset 0x0142b, length 0
    No errors detected in ArcTriomphe-iCCP-red-blue-swap.png (8 chunks, -26.2% compression).

    % pngcheck *.png
    OK: 000000.png (48x48, 1-bit grayscale, non-interlaced, 71.2%).
    OK: 000033.png (48x48, 1-bit colormap, non-interlaced, 66.0%).
    OK: 000066.png (48x48, 1-bit colormap, non-interlaced, 66.0%).
    OK: 000099.png (48x48, 1-bit colormap, non-interlaced, 66.0%).
     [...]
    OK: ffff66.png (48x48, 1-bit colormap, non-interlaced, 66.0%).
    OK: ffff99.png (48x48, 1-bit colormap, non-interlaced, 66.0%).
    OK: ffffcc.png (48x48, 1-bit colormap, non-interlaced, 66.0%).
    OK: ffffff.png (48x48, 1-bit grayscale, non-interlaced, 70.1%).

    No errors were detected in the 216 files tested.

The current release supports all PNG, MNG and JNG chunks, including the newly approved sTER stereo-layout chunk. It correctly reports errors in all but two of the images in Chris Nokleberg's brokensuite-20061204. Also included (since version 2.1.0) are two helper utilities:

• pngsplit - break a PNG, MNG or JNG image into constituent chunks (numbered for easy reassembly)
• png-fix-IDAT-windowsize - fix minor zlib-header breakage caused by libpng 1.2.6

The new utilities are licensed under the GNU General Public License (GPL); pngcheck itself remains under its original, MIT/X11-style license.

• PNG home page
• MNG home page

Copyright © 2000-2007 Greg Roelofs.