On Thu, 05 Apr 2012 20:19:16 -0400
Samuel Bronson <naes...@gmail.com> wrote:
> It would be possible to check "Color type" field first, but there does
> not appear to be any way to do arithmetic on a value read from the
> file before printing it, so I don't see any practical way to get the
> behavior that you want.
Thanks for the pragmatic reply, and ensuing interesting puzzle.
Arithmetic for 'magic' values sounds like a useful feature, so that
could be another 'wishlist' bug.
Fortunately, output more like 'file *.BMP' requires no arithmetic:
0 string \x89PNG\x0d\x0a\x1a\x0a PNG image data,
!:mime image/png
>25 byte 0 grayscale,
>25 byte 2 color RGB,
>25 byte 3 colormap,
>25 byte 4 gray+alpha,
>25 byte 6 color RGBA,
>28 byte 0 non-interlaced
>28 byte 1 interlaced
>16 belong x \b, %ld x
>20 belong x %ld
>25 byte 0
>>24 byte x \b x %d
>25 byte 2
>>24 byte 8 \b x 24
>>24 byte 16 \b x 48
>25 byte 3
>>24 byte x \b x %d
>25 byte 4
>>24 byte 8 \b x 16
>>24 byte 16 \b x 32
>25 byte 6
>>24 byte 8 \b x 32
>>24 byte 16 \b x 64
Which (when copied to '/etc/magic') outputs:
# 'imagemagick' contains various PNGs.
% cd /usr/share/doc/imagemagick/images/ ; file [wn]*.png ; cd - >
/dev/null
navy.png: PNG image data, color RGB, non-interlaced, 64 x 64
x 48
networkredux.png: PNG image data, colormap, interlaced, 140 x 31 x 8
wand.png: PNG image data, color RGBA, non-interlaced, 32 x
32 x 32
white-highlight.png: PNG image data, color RGB, non-interlaced, 70 x 70
x 48
wizard.png: PNG image data, color RGB, non-interlaced, 940 x
1250 x 24
Online PNG references consulted:
http://en.wikipedia.org/wiki/Portable_Network_Graphics#Color_depth
http://www.w3.org/TR/PNG/#11IHDR
http://www.libpng.org/pub/png/book/toc.html
HTH...
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