Small stadalone C program to load png files and print info about their chunks, and other general information (size, trailing data, compression efficiency).
Tries to be robust, not print trash, handle any chunk length, etc. if chunk ID is not letters they will be printed as a hex number (see bad4cc.png below). Should work on any OS and any C compiler. It was also fuzzed with AFL to search for possible crashes, hangs and memory corruptions in malformed PNGs.
On Windows it should build with terminal color and UTF-16 filename support,
this can be verified by presence of line Windows build capable of colors and UTF-16 filenames
in the help/usage message. The UTF-16 filenames in the command output (File '' lines)
they will be printed as UTF-8. On other OSes this line is not present and they are
assumed to be using UTF-8 filenames and have color enabled terminals by default.
If - is used as fileame it will read from stdin. This allows not using a
temporary file on disk when using curl or some program that generates a png
on its stdout, but for a file already on disk it will be slower because piping
data in requires reading it all and discarding the majority of it, while a disk
file can seek and read only the parts that are needed.
On OpenBSD it also uses pledge(2) and unveil(2) to allow only read only access of only the files passed in as arguments, to improve security.
Eval result of +set-bash-completion to set tab completion in bash. The
options meant for bash scripting start with a single + instead of -- to
not be completed when you type in -- and trigger completion.
Note: some examples are from previous versions and the formatting might differ
a little from the latest version, the first two examples (-h and test.png
are always up to date).
$ analyzepng.exe -h
analyzepng.exe - print information about chunks of given png files
Windows build capable of colors and UTF-16 filenames
Usage: analyzepng.exe [--no-idat] file.png... # a single - means read from stdin
--h OR --help #print this help to stdout
--no-idat #don't print IDAT chunk locations and sizes, can be anywhere
--plte #print RGB values from the PLTE chunk
--color-plte #print RGB values from the PLTE chunk using ANSI escape codes
--dont-sort-plte #do not sort the PLTE chunk before printing
--crc #verify CRC checksums of the chunks, slow for big files
+set-bash-completion #print command to set bash completion
+do-bash-completion #do completion based on args from bash
$ analyzepng.exe test.png
File 'test.png'
IHDR, 13 bytes at 16, 206 x 131, 8-bit RGBA
IDAT, 31814 bytes at 41
IEND, 0 bytes at 31867
This PNG has 3 chunks (1 IDAT), 31871 bytes (31.124 KiB), encoding 107944 bytes (105.414 KiB) of image data (29.53%)
Go to releases to download a Windows exe compiled with Pelles C with no -O2
to avoid running into any -O2 optimizer bug similar to this one that affected
stb_image: Pelles C forum bug report
Option --no-idat skips printing IDAT chunks, which can be useful to not clutter
the output if there are very many. Total IDAT count is still displayed at the end.
Use --plte and/or --color-plte to print the palette from the PLTE chunk (if present).
To not sort the palette entries by brightness add --dont-sort-plte.
Option --crc calculates CRC of each chunk and compares it to CRC stored in the file.
$ analyzepng.exe 2000px-Pacman.png
File '2000px-Pacman.png'
IHDR, 13 bytes at 16, 2000 x 2107, 8-bit RGBA
IDAT, 8192 bytes at 41
IDAT, 8192 bytes at 8245
IDAT, 8192 bytes at 16449
IDAT, 8192 bytes at 24653
IDAT, 8192 bytes at 32857
IDAT, 8192 bytes at 41061
IDAT, 8192 bytes at 49265
IDAT, 8087 bytes at 57469
IEND, 0 bytes at 65568
This PNG has 10 chunks (8 IDAT), 65572 bytes (64.035 KiB), encoding 16856000 bytes (16.075 MiB) of image data (0.39%)
$ analyzepng.exe --crc test.png
File 'test.png'
IHDR, 13 bytes at 16, 206 x 131, 8-bit RGBA, OK CRC 0xc5d92476
IDAT, 31814 bytes at 41, OK CRC 0xd26bc80c
IEND, 0 bytes at 31867, OK CRC 0xae426082
This PNG has 3 chunks (1 IDAT), 31871 bytes (31.124 KiB), encoding 107944 bytes (105.414 KiB) of image data (29.53%), 0 bad CRC
$ analyzepng.exe --crc bad4cc.png
File 'bad4cc.png'
IHDR, 13 bytes at 16, 39 x 31, 1-bit paletted, OK CRC 0x5e4446b6
PLTE, 6 bytes at 41, OK CRC 0xa5d99fdd
0x00004154, 125 bytes at 59, WRONG CRC 0x005f858d (computed) 0x5175608a (in file)
IEND, 0 bytes at 196, OK CRC 0xae426082
This PNG has 4 chunks (0 IDAT), 200 bytes (0.195 KiB), encoding 3627 bytes (3.542 KiB) of image data (5.51%), 1 bad CRC
$ analyzepng.exe --no-idat 2000px-Pacman.png
File '2000px-Pacman.png'
IHDR, 13 bytes at 16, 2000 x 2107, 8-bit RGBA
IEND, 0 bytes at 65568
This PNG has: 10 chunks (8 IDAT), 65572 bytes (64.035 KiB) and contains 16856000 bytes (16.075 MiB) of image data (0.39%)
$ analyzepng.exe trailing.png adam7.png
File 'trailing.png'
IHDR, 13 bytes at 16, 39 x 31, 1-bit paletted
PLTE, 6 bytes at 41
IDAT, 125 bytes at 59
IEND, 0 bytes at 196
This PNG has 4 chunks (1 IDAT), 200 bytes (0.195 KiB), encoding 3627 bytes (3.542 KiB) of image data (5.51%)
Error: 6 bytes (0.006 KiB) of trailing data
File 'adam7.png'
IHDR, 13 bytes at 16, 16 x 16, 8-bit RGBA, Adam7 interlaced
bKGD, 6 bytes at 41
pHYs, 9 bytes at 59, 2835 x 2835 pixels per meter
tIME, 7 bytes at 80, 2005-03-10 11:52:57
tEXt, 8 bytes at 99, full (as ASCII + escapes): Comment\0
IDAT, 571 bytes at 119
IEND, 0 bytes at 702
This PNG has 7 chunks (1 IDAT), 706 bytes (0.689 KiB), encoding 1024 bytes (1.000 KiB) of image data (68.95%)
$ analyzepng.exe trailing5gig.png
File 'trailing5gig.png'
IHDR, 13 bytes at 16, 39 x 31, 1-bit paletted
PLTE, 6 bytes at 41
IDAT, 125 bytes at 59
IEND, 0 bytes at 196
This PNG has: 4 chunks (1 IDAT), 200 bytes (0.195 KiB) and contains 3627 bytes (3.542 KiB) of image data (5.51%)
Error: over 15728640 bytes (15.000 MiB) of trailing data
$ analyzepng bmp.bmp jpg.jpg GIF87a.gif GIF89a.gif wav.wav webp.webp mng.mng analyzepng.exe
File 'bmp.bmp'
Error: starts with 'BM', like a BMP file
File 'jpg.jpg'
Error: starts with 0xff 0xd8 0xff, like a JPEG file
File 'GIF87a.gif'
Error: starts with 'GIF', like a GIF file
File 'GIF89a.gif'
Error: starts with 'GIF', like a GIF file
File 'wav.wav'
Error: starts with 'RIFF', but has no 'WEBP' at offset 8
File 'webp.webp'
Error: starts with 'RIFF' and has 'WEBP' on offset 8, like a WEBP file
File 'mng.mng'
Error: MNG 8-byte header valid, this tool only handles PNG
File 'analyzepng.exe'
Error: PNG 8-byte header has unknown wrong values: 0x4d 0x5a 0x90 0x00 0x03 0x00 0x00 0x00 "MZ......"
$ analyzepng.exe bad4cc.png
File 'bad4cc.png'
IHDR, 13 bytes at 16, 39 x 31, 1-bit paletted
PLTE, 6 bytes at 41
0x00004154, 125 bytes at 59
IEND, 0 bytes at 196
This PNG has 4 chunks (0 IDAT), 200 bytes (0.195 KiB), encoding 3627 bytes (3.542 KiB) of image data (5.51%)
$ analyzepng.exe jumpscare.png
File 'jumpscare.png'
IHDR, 13 bytes at 16, 465 x 465, 8-bit RGBA
acTL, 8 bytes at 41, APNG animation control
fcTL, 26 bytes at 61, APNG frame control
IDAT, 98899 bytes at 99
fcTL, 26 bytes at 99010, APNG frame control
fdAT, 236069 bytes at 99048, APNG frame data
IEND, 0 bytes at 335129
This PNG has 7 chunks (1 IDAT), 335133 bytes (327.278 KiB), encoding 864900 bytes (844.629 KiB) of image data (38.75%)