The main justification for this is to provide new libjpeg-turbo users
with a quick & easy way of developing a complete JPEG
compression/decompression program without requiring them to build
libjpeg-turbo from source (which was necessary in order to use the
project-private bmp API) or to use external libraries. These new
functions build upon significant enhancements to rdbmp.c, wrbmp.c,
rdppm.c, and wrppm.c which allow those engines to convert directly
between the native pixel format of the file and a pixel format
("colorspace" in libjpeg parlance) specified by the calling program.
rdbmp.c and wrbmp.c have also been modified such that the calling
program can choose to read or write image rows in the native (bottom-up)
order of the file format, thus eliminating the need to use an inversion
array. tjLoadImage() and tjSaveImage() leverage these new underlying
features in order to significantly improve upon the performance of the
old bmp API.
Because these new functions cannot work without the libjpeg-turbo
colorspace extensions, the libjpeg-compatible code in turbojpeg.c has
been removed. That code was only there to serve as an example of how
to use the TurboJPEG API on top of libjpeg, but more specific, buildable
examples now exist in the https://github.com/libjpeg-turbo/ijg
repository.
Allow progressive entropy coding to be enabled on a
transform-by-transform basis, and implement a new transform option for
disabling the copying of markers.
Closes#153
- Provide a new C API function and TJException method that allows
calling programs to query the severity of a compression/decompression/
transform error.
- Provide a new flag that instructs the library to immediately stop
compressing/decompressing/transforming if a warning is encountered.
Fixes#151
Introduce a new C API function (tjGetErrorStr2()) that can be used to
retrieve compression/decompression/transform error messages in a
thread-safe (i.e. instance-specific) manner. Retrieving error messages
from global functions is still thread-unsafe.
Addresses a concern expressed in #151.
Referring to https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=746,
it seems that the values of local buffer pointers in TurboJPEG API
functions aren't always preserved if longjmp() returns control to a
point prior to the allocation of the local buffers. This is known to
be an issue with GCC 4.x and clang with -O1 and higher optimization
levels but not with GCC 5.x and later. It is unknown why GCC 5.x and
6.x do not suffer from the issue, but possibly the local buffer pointers
are not allocated on the stack when using those more recent compilers.
In any case, this commit modifies the TurboJPEG API library code such
that the jump buffer is always updated after any local buffer pointers
are allocated but before any subsequent libjpeg API functions are
called.
Normally, 4:2:2 JPEGs have horizontal x vertical luminance,chrominance
sampling factors of 2x1,1x1, and 4:4:0 JPEGs have horizontal x vertical
luminance,chrominance sampling factors of 1x2,1x1. However, it is
technically legal to create 4:2:2 JPEGs with sampling factors of
2x2,1x2 and 4:4:0 JPEGs with sampling factors of 2x2,2x1, since the
sums of the products of those sampling factors (2x2 + 1x2 + 1x2 and
2x2 + 2x1 + 2x1) are still <= 10. The libjpeg API correctly decodes
such images, so the TurboJPEG API should as well.
Fixes#92
Even though tjDecompressToYUV2() is mostly just a wrapper for
tjDecompressToYUVPlanes(), tjDecompressToYUV2() still calls
jpeg_read_header(), so it needs to properly set up the libjpeg error
handler prior to making this call. Otherwise, under very esoteric (and
arguably incorrect) use cases, a program can call tjDecompressToYUV2()
without first checking the JPEG header using tjDecompressHeader3(), and
if the header is corrupt, tjDecompressToYUV2() will abort without
triggering an error.
Fixes#72
This addresses a minor concern (LJT-01-002) expressed in a security
audit by Cure53. _tjInitCompress() and _tjInitDecompress() call
(respectively) jpeg_mem_dest_tj() and jpeg_mem_src_tj() with a pointer
to a dummy buffer, in order to set up the destination/source manager.
The dummy buffer should never be used, but it's still better to make it
static so that the pointer in the destination/source manager always
points to a valid region of memory.
This reassures the caller that the buffers will not be modified and also
allows read-only buffers to be passed to the functions.
Partially reverts 3947a19f25fc8186d3812dbcf8e70baea36ef652.
