Update libjpeg-turbo to 1.2.

README-turbo.txt

Index: README-turbo.txt
===================================================================
--- README-turbo.txt	(revision 111873)
+++ README-turbo.txt	(working copy)
@@ -2,7 +2,7 @@
 **     Background
 *******************************************************************************
 
-libjpeg-turbo is a derivative of libjpeg which uses SIMD instructions (MMX,
+libjpeg-turbo is a derivative of libjpeg that uses SIMD instructions (MMX,
 SSE2, etc.) to accelerate baseline JPEG compression and decompression on x86
 and x86-64 systems.  On such systems, libjpeg-turbo is generally 2-4x as fast
 as the unmodified version of libjpeg, all else being equal.
@@ -59,7 +59,7 @@
 **     Using libjpeg-turbo
 *******************************************************************************
 
-libjpeg-turbo includes two APIs which can be used to compress and decompress
+libjpeg-turbo includes two APIs that can be used to compress and decompress
 JPEG images:
 
   TurboJPEG/OSS:  This API wraps libjpeg-turbo and provides an easy-to-use
@@ -122,7 +122,7 @@
 Windows releases can obtain it from the Visual C++ 2008 Redistributable
 Package, which is available as a free download from Microsoft's web site.
 
-NOTE:  Features of libjpeg which require passing a C run time structure, such
+NOTE:  Features of libjpeg that require passing a C run time structure, such
 as a file handle, from an application to libjpeg will probably not work with
 the version of the libjpeg-turbo DLL distributed in the libjpeg-turbo SDK for
 Visual C++, unless the application is also built to use the Visual C++ 2008 C
@@ -208,9 +208,9 @@
 Colorspace Extensions
 =====================
 
-libjpeg-turbo includes extensions which allow JPEG images to be compressed
-directly from (and decompressed directly to) buffers which use BGR, BGRX,
-RGBX, XBGR, and XRGB pixel ordering.  This is implemented with six new
+libjpeg-turbo includes extensions that allow JPEG images to be compressed
+directly from (and decompressed directly to) buffers that use BGR, BGRX,
+RGBX, XBGR, and XRGB pixel ordering.  This is implemented with ten new
 colorspace constants:
 
   JCS_EXT_RGB   /* red/green/blue */
@@ -219,11 +219,15 @@
   JCS_EXT_BGRX  /* blue/green/red/x */
   JCS_EXT_XBGR  /* x/blue/green/red */
   JCS_EXT_XRGB  /* x/red/green/blue */
+  JCS_EXT_RGBA  /* red/green/blue/alpha */
+  JCS_EXT_BGRA  /* blue/green/red/alpha */
+  JCS_EXT_ABGR  /* alpha/blue/green/red */
+  JCS_EXT_ARGB  /* alpha/red/green/blue */
 
 Setting cinfo.in_color_space (compression) or cinfo.out_color_space
 (decompression) to one of these values will cause libjpeg-turbo to read the
 red, green, and blue values from (or write them to) the appropriate position in
-the pixel when YUV conversion is performed.
+the pixel when compressing from/decompressing to an RGB buffer.
 
 Your application can check for the existence of these extensions at compile
 time with:
@@ -233,13 +237,28 @@
 At run time, attempting to use these extensions with a version of libjpeg
 that doesn't support them will result in a "Bogus input colorspace" error.
 
+When using the RGBX, BGRX, XBGR, and XRGB colorspaces during decompression, the
+X byte is undefined, and in order to ensure the best performance, libjpeg-turbo
+can set that byte to whatever value it wishes.  If an application expects the X
+byte to be used as an alpha channel, then it should specify JCS_EXT_RGBA,
+JCS_EXT_BGRA, JCS_EXT_ABGR, or JCS_EXT_ARGB.  When these colorspace constants
+are used, the X byte is guaranteed to be 0xFF, which is interpreted as opaque.
+
+Your application can check for the existence of the alpha channel colorspace
+extensions at compile time with:
+
+  #ifdef JCS_ALPHA_EXTENSIONS
+
+jcstest.c, located in the libjpeg-turbo source tree, demonstrates how to check
+for the existence of the colorspace extensions at compile time and run time.
+
 =================================
 libjpeg v7 and v8 API/ABI support
 =================================
 
 libjpeg v7 and v8 added new features to the API/ABI, and, unfortunately, the
 compression and decompression structures were extended in a backward-
-incompatible manner to accommodate these features.  Thus, programs which are
+incompatible manner to accommodate these features.  Thus, programs that are
 built to use libjpeg v7 or v8 did not work with libjpeg-turbo, since it is
 based on the libjpeg v6b code base.  Although libjpeg v7 and v8 are still not
 as widely used as v6b, enough programs (including a few Linux distros) have
@@ -247,7 +266,7 @@
 API/ABI in libjpeg-turbo.
 
 Some of the libjpeg v7 and v8 features -- DCT scaling, to name one -- involve
-deep modifications to the code which cannot be accommodated by libjpeg-turbo
+deep modifications to the code that cannot be accommodated by libjpeg-turbo
 without either breaking compatibility with libjpeg v6b or producing an
 unsupportable mess.  In order to fully support libjpeg v8 with all of its
 features, we would have to essentially port the SIMD extensions to the libjpeg
@@ -258,8 +277,8 @@
 
 By passing an argument of --with-jpeg7 or --with-jpeg8 to configure, or an
 argument of -DWITH_JPEG7=1 or -DWITH_JPEG8=1 to cmake, you can build a version
-of libjpeg-turbo which emulates the libjpeg v7 or v8 API/ABI, so that programs
-which are built against libjpeg v7 or v8 can be run with libjpeg-turbo.  The
+of libjpeg-turbo that emulates the libjpeg v7 or v8 API/ABI, so that programs
+that are built against libjpeg v7 or v8 can be run with libjpeg-turbo.  The
 following section describes which libjpeg v7+ features are supported and which
 aren't.