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The x86/x86-64 SIMD extensions were originally designed to accommodate changing the value of RGB_*, but this apparently broke when RGB-to-gray colorspace conversion was accelerated. Further, the ARM NEON extensions have always assumed that JCS_RGB behaves identically to JCS_EXT_RGB. Rather than fix these issues, it makes more sense to just stop claiming that we support changing the values of RGB_*, since doing so is no longer necessary.

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git-svn-id: svn+ssh://svn.code.sf.net/p/libjpeg-turbo/code/branches/1.3.x@1298 632fc199-4ca6-4c93-a231-07263d6284db
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DRC
2014-05-13 18:41:33 +00:00
parent 646859004f
commit 4464a39363
1 changed files with 18 additions and 12 deletions
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30
jmorecfg.h
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@@ -298,18 +298,24 @@ typedef int boolean;
/*
* Ordering of RGB data in scanlines passed to or from the application.
* If your application wants to deal with data in the order B,G,R, just
* change these macros. You can also deal with formats such as R,G,B,X
* (one extra byte per pixel) by changing RGB_PIXELSIZE. Note that changing
* the offsets will also change the order in which colormap data is organized.
* RESTRICTIONS:
* 1. The sample applications cjpeg,djpeg do NOT support modified RGB formats.
* 2. These macros only affect RGB<=>YCbCr color conversion, so they are not
* useful if you are using JPEG color spaces other than YCbCr or grayscale.
* 3. The color quantizer modules will not behave desirably if RGB_PIXELSIZE
* is not 3 (they don't understand about dummy color components!). So you
* can't use color quantization if you change that value.
* The RGB_RED, RGB_GREEN, RGB_BLUE, and RGB_PIXELSIZE macros are a vestigial
* feature of libjpeg. The idea was that, if an application developer needed
* to compress from/decompress to a BGR/BGRX/RGBX/XBGR/XRGB buffer, they could
* change these macros, rebuild libjpeg, and link their application statically
* with it. In reality, few people ever did this, because there were some
* severe restrictions involved (cjpeg and djpeg no longer worked properly,
* compressing/decompressing RGB JPEGs no longer worked properly, and the color
* quantizer wouldn't work with pixel sizes other than 3.) Further, since all
* of the O/S-supplied versions of libjpeg were built with the default values
* of RGB_RED, RGB_GREEN, RGB_BLUE, and RGB_PIXELSIZE, many applications have
* come to regard these values as immutable.
*
* The libjpeg-turbo colorspace extensions provide a much cleaner way of
* compressing from/decompressing to buffers with arbitrary component orders
* and pixel sizes. Thus, we do not support changing the values of RGB_RED,
* RGB_GREEN, RGB_BLUE, or RGB_PIXELSIZE. In addition to the restrictions
* listed above, changing these values will also break the SIMD extensions and
* the regression tests.
*/
#define RGB_RED 0 /* Offset of Red in an RGB scanline element */