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@@ -5,7 +5,7 @@ |
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libjpeg-turbo is a high-speed version of libjpeg for x86 and x86-64 processors |
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which uses SIMD instructions (MMX, SSE2, etc.) to accelerate baseline JPEG |
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compression and decompression. libjpeg-turbo is generally 2-4x as fast |
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as the unmodified version of libjpeg, all else being equal. |
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as the unmodified version of libjpeg v6b, all else being equal. |
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libjpeg-turbo was originally based on libjpeg/SIMD by Miyasaka Masaru, but |
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the TigerVNC and VirtualGL projects made numerous enhancements to the codec, |
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@@ -25,21 +25,21 @@ libraries can be used as drop-in replacements for libjpeg on most systems. |
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** License |
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******************************************************************************* |
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Some of the optimizations to the Huffman encoder (jchuff.c) and decoder |
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(jdhuff.c) were borrowed from VirtualGL, and thus any distribution of |
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libjpeg-turbo which includes those optimizations must, as a whole, be subject |
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to the terms of the wxWindows Library Licence, Version 3.1. A copy of this |
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license can be found in this directory under LICENSE.txt. The wxWindows |
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Library License is based on the LGPL but includes provisions which allow the |
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Library to be statically linked into proprietary libraries and applications |
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without requiring the resulting binaries to be distributed under the terms of |
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the LGPL. |
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The TurboJPEG/OSS wrapper, as well as some of the optimizations to the Huffman |
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encoder (jchuff.c) and decoder (jdhuff.c), were borrowed from VirtualGL, and |
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thus any distribution of libjpeg-turbo which includes those files must, as a |
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whole, be subject to the terms of the wxWindows Library Licence, Version 3.1. |
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A copy of this license can be found in this directory under LICENSE.txt. The |
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wxWindows Library License is based on the LGPL but includes provisions which |
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allow the Library to be statically linked into proprietary libraries and |
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applications without requiring the resulting binaries to be distributed under |
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the terms of the LGPL. |
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The rest of the source code, apart from the Huffman codec optimizations, falls |
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under a less restrictive, BSD-style license (see README.) You can choose to |
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distribute libjpeg-turbo, as a whole, under this BSD-style license by simply |
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replacing the optimized jchuff.c and jdhuff.c with their unoptimized |
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counterparts from the libjpeg v6b source. |
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The rest of the source code, apart from TurboJPEG/OSS and the Huffman codec |
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optimizations, falls under a less restrictive, BSD-style license (see README.) |
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You can choose to distribute libjpeg-turbo, as a whole, under this BSD-style |
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license by simply removing TurboJPEG/OSS and replacing the optimized jchuff.c |
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and jdhuff.c with their unoptimized counterparts from the libjpeg v6b source. |
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******************************************************************************* |
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@@ -51,7 +51,7 @@ Replacing libjpeg at Run Time |
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============================= |
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If a Unix application is dynamically linked with libjpeg, then you can replace |
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libjpeg with libjpeg-turbo at run time by manipulating the LD_LIBRARY_PATH. |
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libjpeg with libjpeg-turbo at run time by manipulating LD_LIBRARY_PATH. |
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For instance: |
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[Using libjpeg] |
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@@ -75,36 +75,36 @@ links to the libjpeg dynamic library located in /opt/libjpeg-turbo/{lib}. This |
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will effectively accelerate every dynamically linked libjpeg application on the |
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system. |
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The Windows distribution of the libjpeg-turbo SDK installs jpeg62.dll into |
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c:\libjpeg-turbo\bin, and the PATH environment variable can be modified such |
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that this directory is searched before any others that might contain |
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The libjpeg-turbo SDK for Visual C++ installs jpeg62.dll into |
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c:\libjpeg-turbo[64]\bin, and the PATH environment variable can be modified |
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such that this directory is searched before any others that might contain |
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jpeg62.dll. However, if jpeg62.dll also exists in an application's install |
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directory, then Windows will load the application's version of it first. Thus, |
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if an application ships with jpeg62.dll, then back up the application's version |
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of jpeg62.dll and copy c:\libjpeg-turbo\bin\jpeg62.dll into the application's |
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install directory to accelerate it. |
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of jpeg62.dll and copy c:\libjpeg-turbo[64]\bin\jpeg62.dll into the |
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application's install directory to accelerate it. |
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The version of jpeg62.dll distributed in the libjpeg-turbo SDK requires the |
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Visual C++ 2008 C run time DLL (msvcr90.dll). This library ships with more |
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recent versions of Windows, but users of older versions can obtain it from the |
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Visual C++ 2008 Redistributable Package, which is available as a free download |
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from Microsoft's web site. |
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The version of jpeg62.dll distributed in the libjpeg-turbo SDK for Visual C++ |
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requires the Visual C++ 2008 C run time DLL (msvcr90.dll). msvcr90.dll ships |
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with more recent versions of Windows, but users of older Windows releases can |
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obtain it from the Visual C++ 2008 Redistributable Package, which is available |
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as a free download from Microsoft's web site. |
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NOTE: Features of libjpeg which require passing a C run time structure, such |
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as a file handle, from an application to libjpeg will probably not work with |
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the distributed version of jpeg62.dll unless the application is also built to |
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use the Visual C++ 2008 C run time DLL. In particular, this affects |
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jpeg_stdio_dest() and jpeg_stdio_src(). |
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the version of jpeg62.dll distributed in the libjpeg-turbo SDK for Visual C++, |
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unless the application is also built to use the Visual C++ 2008 C run time DLL. |
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In particular, this affects jpeg_stdio_dest() and jpeg_stdio_src(). |
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Mac applications typically embed their own copies of libjpeg.62.dylib inside |
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the (hidden) application bundle, so it is not possible to globally replace |
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libjpeg on OS X systems. If an application uses a shared library version of |
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libjpeg, then it may be possible to replace the application's version of it. |
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This would generally involve copying libjpeg.62.dylib into the appropriate |
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place in the application bundle and using install_name_tool to repoint the |
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dylib to the new directory. This requires an advanced knowledge of OS X and |
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would not survive an upgrade or a re-install of the application. Thus, it is |
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not recommended for most users. |
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This would generally involve copying libjpeg.62.dylib from libjpeg-turbo into |
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the appropriate place in the application bundle and using install_name_tool to |
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repoint the dylib to the new directory. This requires an advanced knowledge of |
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OS X and would not survive an upgrade or a re-install of the application. |
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Thus, it is not recommended for most users. |
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======================= |
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Replacing TurboJPEG/IPP |
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@@ -115,8 +115,8 @@ VirtualGL 2.1.x and TurboVNC 0.6 (and prior.) libjpeg-turbo contains a wrapper |
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library (TurboJPEG/OSS) that emulates the TurboJPEG API using libjpeg-turbo |
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instead of the closed source Intel Performance Primitives. You can replace the |
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TurboJPEG/IPP package on Linux systems with the libjpeg-turbo package in order |
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to make existing releases of VirtualGL 2.1.x and TurboVNC use the new codec at |
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run time. Note that the 64-bit libjpeg-turbo packages contain only 64-bit |
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to make existing releases of VirtualGL 2.1.x and TurboVNC 0.x use the new codec |
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at run time. Note that the 64-bit libjpeg-turbo packages contain only 64-bit |
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binaries, whereas the TurboJPEG/IPP 64-bit packages contained both 64-bit and |
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32-bit binaries. Thus, to replace a TurboJPEG/IPP 64-bit package, install |
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both the 64-bit and 32-bit versions of libjpeg-turbo. |
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@@ -132,8 +132,8 @@ Using libjpeg-turbo in Your Own Programs |
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For the most part, libjpeg-turbo should work identically to libjpeg, so in |
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most cases, an application can be built against libjpeg and then run against |
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libjpeg-turbo. On Unix systems, you can build against libjpeg-turbo instead |
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of libjpeg by setting |
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libjpeg-turbo. On Unix systems (including Cygwin), you can build against |
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libjpeg-turbo instead of libjpeg by setting |
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CPATH=/opt/libjpeg-turbo/include |
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and |
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@@ -142,12 +142,6 @@ of libjpeg by setting |
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({lib} = lib32 or lib64, depending on whether you are building a 32-bit or a |
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64-bit application.) |
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If using Cygwin, then set |
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CPATH=/cygdrive/c/libjpeg-turbo-gcc[64]/include |
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and |
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LIBRARY_PATH=/cygdrive/c/libjpeg-turbo-gcc[64]/lib |
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If using MinGW, then set |
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CPATH=/c/libjpeg-turbo-gcc[64]/include |
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@@ -156,11 +150,11 @@ If using MinGW, then set |
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Building against libjpeg-turbo is useful, for instance, if you want to build an |
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application that leverages the libjpeg-turbo colorspace extensions (see below.) |
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On Linux and Solaris systems, you would still need to manipulate the |
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LD_LIBRARY_PATH or sym links appropriately to use libjpeg-turbo at run time. |
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On such systems, you can pass -R /opt/libjpeg-turbo/{lib} to the linker to |
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force the use of libjpeg-turbo at run time rather than libjpeg (also useful if |
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you want to leverage the colorspace extensions), or you can link against the |
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On Linux and Solaris systems, you would still need to manipulate |
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LD_LIBRARY_PATH or create appropriate sym links to use libjpeg-turbo at run |
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time. On such systems, you can pass -R /opt/libjpeg-turbo/{lib} to the linker |
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to force the use of libjpeg-turbo at run time rather than libjpeg (also useful |
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if you want to leverage the colorspace extensions), or you can link against the |
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libjpeg-turbo static library. |
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To force a Linux, Solaris, or MinGW application to link against the static |
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@@ -172,8 +166,8 @@ On OS X, simply add /opt/libjpeg-turbo/lib/libjpeg.a to the linker command |
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line (this also works on Linux and Solaris.) |
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To build Visual C++ applications using libjpeg-turbo, add |
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c:\libjpeg-turbo[64]\include to your system or user INCLUDE environment |
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variable and c:\libjpeg-turbo[64]\lib to your system or user LIB environment |
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c:\libjpeg-turbo[64]\include to the system or user INCLUDE environment |
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variable and c:\libjpeg-turbo[64]\lib to the system or user LIB environment |
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variable, and then link against either jpeg.lib (to use jpeg62.dll) or |
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jpeg-static.lib (to use the static version of libjpeg-turbo.) |
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@@ -182,8 +176,8 @@ Colorspace Extensions |
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===================== |
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libjpeg-turbo includes extensions which allow JPEG images to be compressed |
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directly from (and decompressed directly to) buffers which use BGR, BGRA, |
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RGBA, ABGR, and ARGB pixel ordering. This is implemented with six new |
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directly from (and decompressed directly to) buffers which use BGR, BGRX, |
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RGBX, XBGR, and XRGB pixel ordering. This is implemented with six new |
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colorspace constants: |
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JCS_EXT_RGB /* red/green/blue */ |
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@@ -205,3 +199,31 @@ time with: |
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At run time, attempting to use these extensions with a version of libjpeg |
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that doesn't support them will result in a "Bogus input colorspace" error. |
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******************************************************************************* |
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** Performance pitfalls |
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******************************************************************************* |
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=============== |
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Restart Markers |
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=============== |
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The optimized Huffman decoder in libjpeg-turbo does not handle restart markers |
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in a way that makes libjpeg happy, so it is necessary to use the slow Huffman |
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decoder when decompressing a JPEG image that has restart markers. This can |
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cause the decompression performance to drop by as much as 20%, but the |
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performance will still be much much greater than that of libjpeg v6b. Many |
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consumer packages, such as PhotoShop, use restart markers when generating JPEG |
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images, so images generated by those programs will experience this issue. |
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=============================================== |
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Fast Integer Forward DCT at High Quality Levels |
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=============================================== |
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The algorithm used by the SIMD-accelerated quantization function cannot produce |
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correct results whenever the fast integer forward DCT is used along with a JPEG |
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quality of 98-100. Thus, libjpeg-turbo must use the non-SIMD quantization |
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function in those cases. This causes performance to drop by as much as 40%. |
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It is therefore strongly advised that you use the slow integer forward DCT |
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whenever encoding images with a JPEG quality of 98 or higher. |
DRC
13 years ago
