I've been using IM to work with large (28800x28800px) satellite
imagery, stored in grayscale tiff format. (See here: http://
telascience.sdsc.edu/tela_data/onearth/ ) I've been using IM to
translate from TIFF format to PNG. After a recent IM upgrade, I
noticed that things weren't quite right, namely other programs
weren't able to load the translated PNGs because they required too
much memory.
I think I've tracked it down to ImageMagick. Somewhere between v6.2.9
and v6.3.4 IM has started treating grayscale TIFFs as true color,
thus requiring 4x the memory. I was able to replicate this with a
grayscale TIFF saved out of Photoshop (but not a palette TIFF). You
can download my example TIFF here:
http://pricepages.org/temp/grayscale.tif
Example with IM v6.2.9:
% identify grayscale.tif
grayscale.tif TIFF 720x529 720x529+0+0 PseudoClass 256c 8-bit 24.293kb
% identify B4N036W108.tif
B4N036W108.tif TIFF 28800x28800 28800x28800+0+0 PseudoClass 256c 8-
bit 791.236mb 29.270u 3:51
identify: B4N036W108.tif: unknown field with tag 33550 (0x830e)
encountered. `TIFFReadDirectory'.
identify: B4N036W108.tif: unknown field with tag 33922 (0x8482)
encountered. `TIFFReadDirectory'.
identify: B4N036W108.tif: unknown field with tag 34735 (0x87af)
encountered. `TIFFReadDirectory'.
identify: B4N036W108.tif: unknown field with tag 34737 (0x87b1)
encountered. `TIFFReadDirectory'.
Example with IM v6.3.4:
% identify grayscale.tif
grayscale.tif TIFF 720x529 720x529+0+0 DirectClass 8-bit 24.293kb
% identify B4N036W108.tif
B4N036W108.tif TIFF 28800x28800 28800x28800+0+0 DirectClass 8-bit
791.236mb 17.000u 2:41
identify: B4N036W108.tif: unknown field with tag 33550 (0x830e)
encountered. `TIFFReadDirectory'.
identify: B4N036W108.tif: unknown field with tag 33922 (0x8482)
encountered. `TIFFReadDirectory'.
identify: B4N036W108.tif: unknown field with tag 34735 (0x87af)
encountered. `TIFFReadDirectory'.
identify: B4N036W108.tif: unknown field with tag 34737 (0x87b1)
encountered. `TIFFReadDirectory'.
(Ignore the unknown tags, they are GeoTIFF specific data.)
Is this a bug? How can I revert back to v6.2.9 behavior?
Thanks,
Seth
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