[Magick-bugs] Odd bug when reading raw gray image

[duc.sequere.aut.de.via.decede at imagemagick.org]

> Strange how the size of the file affects convert.

Unless you explicitedly set the image type (e.g. gray:image.gray) ImageMagick
looks at the first few bytes of the file to determine if it has a magic
number that matches one of the many image formats ImageMagick supports.  Your
gray image just happen to have a few bytes that produced a false positive and
made ImageMagick think it was a different file format rather than raw gray.
The explicit gray: tells ImageMagick to not look at magic numbers in the image
header and assume the image is always raw gray.