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libjpeg-turbo is a derivative of libjpeg that uses SIMD instructions (MMX,
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SSE2, NEON) to accelerate baseline JPEG compression and decompression on x86,
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x86-64, and ARM systems. On such systems, libjpeg-turbo is generally 2-4x as
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fast as the unmodified version of libjpeg, 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 in
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2009, including improved support for Mac OS X, 64-bit support, support for
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32-bit and big-endian pixel formats (RGBX, XBGR, etc.), accelerated Huffman
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encoding/decoding, and various bug fixes. The goal was to produce a fully
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open-source codec that could replace the partially closed-source TurboJPEG/IPP
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codec used by VirtualGL and TurboVNC. libjpeg-turbo generally achieves 80-120%
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of the performance of TurboJPEG/IPP. It is faster in some areas but slower in
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In early 2010, libjpeg-turbo spun off into its own independent project, with
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the goal of making high-speed JPEG compression/decompression technology
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available to a broader range of users and developers.
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*******************************************************************************
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*******************************************************************************
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Most of libjpeg-turbo inherits the non-restrictive, BSD-style license used by
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libjpeg (see README.) The TurboJPEG/OSS wrapper (both C and Java versions) and
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associated test programs bear a similar license, which is reproduced below:
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Redistribution and use in source and binary forms, with or without
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modification, are permitted provided that the following conditions are met:
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- Redistributions of source code must retain the above copyright notice,
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this list of conditions and the following disclaimer.
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- Redistributions in binary form must reproduce the above copyright notice,
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this list of conditions and the following disclaimer in the documentation
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and/or other materials provided with the distribution.
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- Neither the name of the libjpeg-turbo Project nor the names of its
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contributors may be used to endorse or promote products derived from this
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software without specific prior written permission.
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS",
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AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
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LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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POSSIBILITY OF SUCH DAMAGE.
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*******************************************************************************
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** Using libjpeg-turbo
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*******************************************************************************
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libjpeg-turbo includes two APIs that can be used to compress and decompress
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TurboJPEG API: This API provides an easy-to-use interface for compressing
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and decompressing JPEG images in memory. It also provides some functionality
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that would not be straightforward to achieve using the underlying libjpeg
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API, such as generating planar YUV images and performing multiple
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simultaneous lossless transforms on an image. The Java interface for
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libjpeg-turbo is written on top of the TurboJPEG API.
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libjpeg API: This is the de facto industry-standard API for compressing and
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decompressing JPEG images. It is more difficult to use than the TurboJPEG
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API but also more powerful. libjpeg-turbo is both API/ABI-compatible and
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mathematically compatible with libjpeg v6b. It can also optionally be
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configured to be API/ABI-compatible with libjpeg v7 and v8 (see below.)
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=============================
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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 LD_LIBRARY_PATH.
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> time cjpeg <vgl_5674_0098.ppm >vgl_5674_0098.jpg
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> export LD_LIBRARY_PATH=/opt/libjpeg-turbo/{lib}:$LD_LIBRARY_PATH
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> time cjpeg <vgl_5674_0098.ppm >vgl_5674_0098.jpg
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NOTE: {lib} can be lib, lib32, lib64, or lib/64, depending on the O/S and
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System administrators can also replace the libjpeg sym links in /usr/{lib} with
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links to the libjpeg-turbo dynamic library located in /opt/libjpeg-turbo/{lib}.
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This will effectively accelerate every application that uses the libjpeg
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dynamic library on the system.
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The libjpeg-turbo SDK for Visual C++ installs the libjpeg-turbo DLL
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(jpeg62.dll, jpeg7.dll, or jpeg8.dll, depending on whether it was built with
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libjpeg v6b, v7, or v8 emulation) into c:\libjpeg-turbo[64]\bin, and the PATH
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environment variable can be modified such that this directory is searched
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before any others that might contain a libjpeg DLL. However, if a libjpeg
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DLL exists in an application's install directory, then Windows will load this
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DLL first whenever the application is launched. Thus, if an application ships
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with jpeg62.dll, jpeg7.dll, or jpeg8.dll, then back up the application's
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version of this DLL and copy c:\libjpeg-turbo[64]\bin\jpeg*.dll into the
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application's install directory to accelerate it.
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The version of the libjpeg-turbo DLL distributed in the libjpeg-turbo SDK for
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Visual C++ requires the Visual C++ 2008 C run-time DLL (msvcr90.dll).
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msvcr90.dll ships with more recent versions of Windows, but users of older
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Windows releases can obtain it from the Visual C++ 2008 Redistributable
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Package, which is available as a free download from Microsoft's web site.
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NOTE: Features of libjpeg that 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 version of the libjpeg-turbo DLL distributed in the libjpeg-turbo SDK for
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Visual C++, unless the application is also built to use the Visual C++ 2008 C
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run-time DLL. In particular, this affects jpeg_stdio_dest() and
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Mac applications typically embed their own copies of the libjpeg 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.*.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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=======================
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libjpeg-turbo is a drop-in replacement for the TurboJPEG/IPP SDK used by
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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 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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You can also build the VirtualGL 2.1.x and TurboVNC 0.6 source code with
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the libjpeg-turbo SDK instead of TurboJPEG/IPP. It should work identically.
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libjpeg-turbo also includes static library versions of TurboJPEG/OSS, which
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are used to build VirtualGL 2.2 and TurboVNC 1.0 and later.
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========================================
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Using libjpeg-turbo in Your Own Programs
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========================================
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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 (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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LIBRARY_PATH=/opt/libjpeg-turbo/{lib}
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({lib} = lib32 or lib64, depending on whether you are building a 32-bit or a
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If using MinGW, then set
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CPATH=/c/libjpeg-turbo-gcc[64]/include
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LIBRARY_PATH=/c/libjpeg-turbo-gcc[64]/lib
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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
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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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version of libjpeg-turbo, you can use the following linker options:
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-Wl,-Bstatic -ljpeg -Wl,-Bdynamic
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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 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 the DLL version of
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libjpeg-turbo) or jpeg-static.lib (to use the static version of libjpeg-turbo.)
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=====================
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Colorspace Extensions
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=====================
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libjpeg-turbo includes extensions that allow JPEG images to be compressed
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directly from (and decompressed directly to) buffers that use BGR, BGRX,
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RGBX, XBGR, and XRGB pixel ordering. This is implemented with ten new
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colorspace constants:
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JCS_EXT_RGB /* red/green/blue */
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JCS_EXT_RGBX /* red/green/blue/x */
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JCS_EXT_BGR /* blue/green/red */
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JCS_EXT_BGRX /* blue/green/red/x */
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JCS_EXT_XBGR /* x/blue/green/red */
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JCS_EXT_XRGB /* x/red/green/blue */
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JCS_EXT_RGBA /* red/green/blue/alpha */
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JCS_EXT_BGRA /* blue/green/red/alpha */
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JCS_EXT_ABGR /* alpha/blue/green/red */
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JCS_EXT_ARGB /* alpha/red/green/blue */
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Setting cinfo.in_color_space (compression) or cinfo.out_color_space
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(decompression) to one of these values will cause libjpeg-turbo to read the
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red, green, and blue values from (or write them to) the appropriate position in
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the pixel when compressing from/decompressing to an RGB buffer.
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Your application can check for the existence of these extensions at compile
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#ifdef JCS_EXTENSIONS
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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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When using the RGBX, BGRX, XBGR, and XRGB colorspaces during decompression, the
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X byte is undefined, and in order to ensure the best performance, libjpeg-turbo
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can set that byte to whatever value it wishes. If an application expects the X
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byte to be used as an alpha channel, then it should specify JCS_EXT_RGBA,
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JCS_EXT_BGRA, JCS_EXT_ABGR, or JCS_EXT_ARGB. When these colorspace constants
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are used, the X byte is guaranteed to be 0xFF, which is interpreted as opaque.
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Your application can check for the existence of the alpha channel colorspace
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extensions at compile time with:
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#ifdef JCS_ALPHA_EXTENSIONS
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jcstest.c, located in the libjpeg-turbo source tree, demonstrates how to check
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for the existence of the colorspace extensions at compile time and run time.
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=================================
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libjpeg v7 and v8 API/ABI support
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=================================
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With libjpeg v7 and v8, new features were added that necessitated extending the
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compression and decompression structures. Unfortunately, due to the exposed
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nature of those structures, extending them also necessitated breaking backward
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ABI compatibility with previous libjpeg releases. Thus, programs that are
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built to use libjpeg v7 or v8 did not work with libjpeg-turbo, since it is
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based on the libjpeg v6b code base. Although libjpeg v7 and v8 are still not
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as widely used as v6b, enough programs (including a few Linux distros) have
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made the switch that it was desirable to provide support for the libjpeg v7/v8
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API/ABI in libjpeg-turbo. Although libjpeg-turbo can now be configured as a
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drop-in replacement for libjpeg v7 or v8, it should be noted that not all of
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the features in libjpeg v7 and v8 are supported (see below.)
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By passing an argument of --with-jpeg7 or --with-jpeg8 to configure, or an
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argument of -DWITH_JPEG7=1 or -DWITH_JPEG8=1 to cmake, you can build a version
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of libjpeg-turbo that emulates the libjpeg v7 or v8 API/ABI, so that programs
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that are built against libjpeg v7 or v8 can be run with libjpeg-turbo. The
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following section describes which libjpeg v7+ features are supported and which
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libjpeg v7 and v8 Features:
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---------------------------
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-- cjpeg: Separate quality settings for luminance and chrominance
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Note that the libpjeg v7+ API was extended to accommodate this feature only
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for convenience purposes. It has always been possible to implement this
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feature with libjpeg v6b (see rdswitch.c for an example.)
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-- cjpeg: 32-bit BMP support
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-- jpegtran: lossless cropping
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-- jpegtran: -perfect option
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-- rdjpgcom: -raw option
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-- rdjpgcom: locale awareness
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Fully supported when using libjpeg v7/v8 emulation:
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-- libjpeg: In-memory source and destination managers
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-- libjpeg: DCT scaling in compressor
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cinfo.scale_num and cinfo.scale_denom are silently ignored.
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There is no technical reason why DCT scaling cannot be supported, but
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without the SmartScale extension (see below), it would only be able to
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down-scale using ratios of 1/2, 8/15, 4/7, 8/13, 2/3, 8/11, 4/5, and 8/9,
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which is of limited usefulness.
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-- libjpeg: SmartScale
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cinfo.block_size is silently ignored.
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SmartScale is an extension to the JPEG format that allows for DCT block
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sizes other than 8x8. It would be difficult to support this feature while
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retaining backward compatibility with libjpeg v6b.
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-- libjpeg: IDCT scaling extensions in decompressor
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libjpeg-turbo still supports IDCT scaling with scaling factors of 1/2, 1/4,
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and 1/8 (same as libjpeg v6b.)
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-- libjpeg: Fancy downsampling in compressor
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cinfo.do_fancy_downsampling is silently ignored.
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This requires the DCT scaling feature, which is not supported.
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This requires both the DCT scaling and SmartScale features, which are not
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-- Lossless RGB JPEG files
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This requires the SmartScale feature, which is not supported.
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*******************************************************************************
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** Performance pitfalls
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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 the rest of the libjpeg infrastructure happy, so it is
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necessary to use the slow Huffman decoder when decompressing a JPEG image that
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has restart markers. This can cause the decompression performance to drop by
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as much as 20%, but the performance will still be much greater than that of
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libjpeg. Many consumer packages, such as PhotoShop, use restart markers when
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generating JPEG images, so images generated by those programs will experience
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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.
added
removed
src/libjpeg-turbo/README-turbo.txt
