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Section - [16] What other common
compatibility problems are there?
Aside from the file format difficulties mentioned in the previous section, there are a few other common
causes of trouble with transferring JPEGs.
Old decoders that don't handle progressive JPEG will often give rather cryptic error messages when fed
a progressive JPEG. If you get a complaint like "Unsupported marker type 0xC2", then you definitely
have a progressive JPEG file and a non-progressive-capable decoder. (See part 2 of this FAQ for infor-
mation about more up-to-date programs.) Or you may get a generic error message that claims the file is
corrupted or isn't JPEG at all.
Adobe Photoshop and some other prepress-oriented applications will produce four-channel CMYK JPEG
files when asked to save a JPEG from CMYK image mode. Hardly anything that's not prepress-savvy
will cope with CMYK JPEGs (or any other CMYK format for that matter). When making JPEGs for Web
use, be sure to save from RGB or grayscale mode.
Photoshop also has a habit of stuffing a rather large thumbnail/preview image into an application-private
segment of JPEG files. Some other applications (notably early releases of Sun's Java library) are known
to choke on this data. This is definitely a bug in those other applications, but the best available workar-
ound is still to tell Photoshop not to save a thumbnail. If you're putting up an image on the Web, having a
thumbnail embedded in it is just a waste of download time anyway.
When transferring images between machines running different operating systems, be very careful to get
a straight "binary" transfer --- any sort of text format conversion will corrupt a JPEG file. Actually that's
true for all image formats not just JPEG. |
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