which command can judge whether a png pic has alpha channel ？

[zxsz4084]

Dear Qins：
which command can judge whether a png pic has alpha channel ？

[glennrp]

My favorite is "pngcheck", which you can get fromhttp://www.libpng.org/pub/png/apps/pngcheck.html

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pngcheck file.png

On *nix, you have "file" and can type

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file file.png

(although this will miss PNG files where the alpha is conveyed via the tRNS chunk).

If you prefer to use ImageMagick, type

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identify -verbose file.png

and look for lines containing "png:IHDR.color_type:" and "png:tRNS"

[fmw42]

see string format %[channels] or %[opaque] at http://www.imagemagick.org/script/escape.php

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convert image -format " %[channels]" info:

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convert image -format " %[opaque]" info: