In article ,
Clyde wrote:
None of them that I saw say or imply that CMYK is an Adobe addition. Photoshop’s Help file on "JPEG format" says that CMYK is part of JPEG. Do you have something to back up your statement?
Have you tried anything with a CMYK JPEG file? True, IE6 and FireFox won’t open a CMYK JPEG file, but just about everything else on my computer will. All my Adobe products will. CorelDraw & CorelPaint will. All my Microsoft products will, including all of Office 2003. Windows XP doesn’t see anything special about a JPEG file in CMYK mode.
There is no reason for a browser to need to open a JPEG CMYK file, except to follow a standard. Microsoft does follow standards, when they aren’t making their own. They aren’t in the habit of just adopting Adobe stuff as standard.
As far as I can tell CMYK is a legitimate and proper mode for standard JPEG. Please provide evidence that I’m wrong.
The JPEG standard is documented here:
http://en.wikipedia.org/wiki/Jpeg You will note that the published standard defines only a way to convert from RGB color to the JPEG internal Y Cb Cr color format.
CMYK is not included in the JPEG standard. It is, however, included in the JPEG 2000 ( .jp2 file format) standard; in fact, the JPEG 2000 standard was invented to correct shortcomings in the JPEG standard, including lack of CMYK support. It is important to note that a JPEG 2000 file is not a JPEG file; programs which can open JPEGs can not necessarily open JPEG 2000 files.
http://www.accusoft.com/imaging/imagegear/imagegear_function s/jpeg_2000.a sp
The JPEG Metadata Specification and Usage Notes at
http://java.sun.com/j2se/1.4.2/docs/api/javax/imageio/metada ta/doc-files/ jpeg_metadata.html
read, in part, "If an Adobe APP14 marker segment is present, the colorspace is determined by consulting the transform flag. The transform flag takes one of three values:
2 – The image is encoded as YCCK (implicitly converted from CMYK on encoding).
1 – The image is encoded as YCbCr (implicitly converted from RGB on encoding).
0 – Unknown. 3-channel images are assumed to be RGB, 4-channel images are assumed to be CMYK."
APP tags are application-specific tags within a JPEG JFIF file; they are a means to extend the standard. Adobe invented the APP13 and APP14 tags defining a CMYK file.
Microsoft and other companies routinely implement graphics file formats and extensions invented elsewhere; the TIFF format, for instance, was invented by Aldus and extended by (and currently owned by) Adobe, yet Microsoft apps can read TIFF files!
The document at
http://www.dansdata.com/graphics.htm says "CMYK this support was added in a later version of the standard, though." It does not elaborate on the fact that this support was first created by Adobe, which is unfortunate. There is, however, a very old document at
http://www.boxtopsoft.com/projpeg_faq.html which reads
"There is a second common format for JPEG called Adobe JPEG, which is the file format saved by Adobe Photoshop when you save a JPEG though Photoshop. This format is almost as widely support as the JFIF variety, but does pose more compatibility issues with browsers than JFIF. Adobe JPEG supports saving files in CMYK color mode, which are not viewable in most current browsers, not just incompatible with very old browsers."
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