USING THE IJG JPEG LIBRARY
Copyright (C) 1994-2013, Thomas G. Lane, Guido Vollbeding.
This file is part of the Independent JPEG Group's software.
For conditions of distribution and use, see the accompanying README file.
This file describes how to use the IJG JPEG library within an application
program. Read it if you want to write a program that uses the library.
The file example.c provides heavily commented skeleton code for calling the
JPEG library. Also see jpeglib.h (the include file to be used by application
programs) for full details about data structures and function parameter lists.
The library source code, of course, is the ultimate reference.
Note that there have been *major* changes from the application interface
presented by IJG version 4 and earlier versions. The old design had several
inherent limitations, and it had accumulated a lot of cruft as we added
features while trying to minimize application-interface changes. We have
sacrificed backward compatibility in the version 5 rewrite, but we think the
improvements justify this.
TABLE OF CONTENTS
-----------------
Overview:
Functions provided by the library
Outline of typical usage
Basic library usage:
Data formats
Compression details
Decompression details
Mechanics of usage: include files, linking, etc
Advanced features:
Compression parameter selection
Decompression parameter selection
Special color spaces
Error handling
Compressed data handling (source and destination managers)
I/O suspension
Progressive JPEG support
Buffered-image mode
Abbreviated datastreams and multiple images
Special markers
Raw (downsampled) image data
Really raw data: DCT coefficients
Progress monitoring
Memory management
Memory usage
Library compile-time options
Portability considerations
Notes for MS-DOS implementors
You should read at least the overview and basic usage sections before trying
to program with the library. The sections on advanced features can be read
if and when you need them.
OVERVIEW
========
Functions provided by the library
---------------------------------
The IJG JPEG library provides C code to read and write JPEG-compressed image
files. The surrounding application program receives or supplies image data a
scanline at a time, using a straightforward uncompressed image format. All
details of color conversion and other preprocessing/postprocessing can be
handled by the library.
The library includes a substantial amount of code that is not covered by the
JPEG standard but is necessary for typical applications of JPEG. These
functions preprocess the image before JPEG compression or postprocess it after
decompression. They include colorspace conversion, downsampling/upsampling,
and color quantization. The application indirectly selects use of this code
by specifying the format in which it wishes to supply or receive image data.
For example, if colormapped output is requested, then the decompression
library automatically invokes color quantization.
A wide range of quality vs. speed tradeoffs are possible in JPEG processing,
and even more so in decompression postprocessing. The decompression library
provides multiple implementations that cover most of the useful tradeoffs,
ranging from very-high-quality down to fast-preview operation. On the
compression side we have generally not provided low-quality choices, since
compression is normally less time-critical. It should be understood that the
low-quality modes may not meet the JPEG standard's accuracy requirements;
nonetheless, they are useful for viewers.
A word about functions *not* provided by the library. We handle a subset of
the ISO JPEG standard; most baseline, extended-sequential, and progressive
JPEG processes are supported. (Our subset includes all features now in common
use.) Unsupported ISO options include:
* Hierarchical storage
* Lossless JPEG
* DNL marker
* Nonintegral subsampling ratios
We support 8-bit to 12-bit data precision, but this is a compile-time choice
rather than a run-time choice; hence it is difficult to use different
precisions in a single application.
By itself, the library handles only interchange JPEG datastreams --- in
particular the widely used JFIF file format. The library can be used by
surrounding code to process interchange or abbreviated JPEG datastreams that
are embedded in more complex file formats. (For example, this library is
used by the free LIBTIFF library to support JPEG compression in TIFF.)
Outline of typical usage
------------------------
The rough outline of a JPEG compression operation is:
Allocate and initialize a JPEG compression object
Specify the destination for the compressed data (eg, a file)
Set parameters for compression, including image size & colorspace
jpeg_start_compress(...);
while (scan lines remain to be written)
jpeg_write_scanlines(...);
jpeg_finish_compress(...);
Release the JPEG compression object
A JPEG compression object holds parameters and working state for the JPEG
library. We make creation/destruction of the object separate from starting
or finishing compression of an image; the same object can be re-used for a
series of image compression operations. This makes it easy to re-use the
same parameter settings for a sequence of images. Re-use of a JPEG object
also has important implications for processing abbreviated JPEG datastreams,
as discussed later.
The image data to be compressed is supplied to jpeg_write_scanlines() from
in-memory buffers. If the application is doing file-to-file compression,
reading image data from the source file is the application's responsibility.
The library emits compressed data by calling a "data destination manager",
which typically will write the data into a file; but the application can
provide its own destination manager to do something else.
Similarly, the rough outline of a JPEG decompression operation is:
Allocate and initialize a JPEG decompression object
Specify the source of the compressed data (eg, a file)
Call jpeg_read_header() to obtain image info
Set parameters for decompression
jpeg_start_decompress(...);
while (scan lines remain to be read)
jpeg_read_scanlines(...);
jpeg_finish_decompress(...);
Release the JPEG decompression object
This is comparable to the compression outline except that reading the
datastream header is a separate step. This is helpful because information
about the image's size, colorspace, etc is available when the application
selects decompression parameters. For example, the application can choose an
output scaling ratio that will fit the image into the available screen size.
The decompression library obtains compressed data by calling a data source
manager, which typically will read the data from a file; but other behaviors
can be obtained with a custom source manager. Decompressed data is delivered
into in-memory buffers passed to jpeg_read_scanlines().
It is possible to abort an incomplete compression or decompression operation
by calling jpeg_abort(); or, if you do not need to retain the JPEG object,
simply release it by calling jpeg_destroy().
JPEG compression and decompression objects are two separate struct types.
However, they share some common fields, and certain routines such as
jpeg_destroy() can work on either type of object.
The JPEG library has no static variables: all state is in the compression
or decompression object. Therefore it is possible to process multiple
compression and decompression operations concurrently, using multiple JPEG
objects.
Both compression and decompression can be done in an incremental memory-to-
memory fashion, if suitable source/destination managers are used. See the
section on "I/O suspension" for more details.
BASIC LIBRARY USAGE
===================
Data formats
------------
B
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STM32F429制作视频播放器【STM32F42X系列单片机_寄存器驱动】.zip (428个子文件)
cjpeg.1 14KB
jpegtran.1 10KB
djpeg.1 8KB
wrjpgcom.1 3KB
rdjpgcom.1 2KB
configure.ac 12KB
Makefile.am 5KB
makefile.ansi 12KB
ar-lib 6KB
jmemdosa.asm 8KB
makefile.bcc 15KB
jconfig.bcc 1KB
testimg.bmp 34KB
cc936.c 708KB
cc949.c 555KB
cc950.c 441KB
cc932.c 244KB
ff.c 189KB
jidctint.c 183KB
jfdctint.c 159KB
inv_mpu.c 105KB
transupp.c 64KB
lcd.c 59KB
inv_mpu_dmp_motion_driver.c 57KB
jdhuff.c 49KB
jquant2.c 49KB
jchuff.c 48KB
jdmarker.c 46KB
data_builder.c 45KB
jmemmgr.c 41KB
tjpgd.c 41KB
sdio_sdcard.c 38KB
jquant1.c 31KB
jcmaster.c 31KB
jcarith.c 28KB
jdcoefct.c 26KB
jdinput.c 25KB
nand.c 25KB
ccsbcs.c 25KB
ml_math_func.c 25KB
jdarith.c 24KB
jcparam.c 24KB
jdcolor.c 24KB
cjpeg.c 22KB
jdmerge.c 21KB
jdmainct.c 21KB
jcsample.c 20KB
djpeg.c 20KB
jccolor.c 20KB
jdmaster.c 20KB
jcmarker.c 19KB
jmemdos.c 19KB
jpegtran.c 19KB
ftl.c 18KB
hal_outputs.c 18KB
ltdc.c 18KB
example.c 17KB
wrjpgcom.c 17KB
jccoefct.c 17KB
results_holder.c 16KB
jcdctmgr.c 16KB
gif.c 16KB
touch.c 15KB
rdbmp.c 15KB
rdtarga.c 15KB
usmart.c 15KB
rdjpgcom.c 15KB
bmp.c 14KB
rdppm.c 14KB
jctrans.c 14KB
wrbmp.c 14KB
jidctfst.c 13KB
wrgif.c 13KB
jdapimin.c 13KB
ov5640.c 13KB
jddctmgr.c 12KB
jcprepct.c 12KB
ckconfig.c 12KB
jdsample.c 12KB
videoplayer.c 12KB
exfuns.c 12KB
rdrle.c 12KB
usmart_str.c 12KB
w25qxx.c 11KB
eMPL_outputs.c 11KB
rdswitch.c 11KB
recorder.c 11KB
app4.c 10KB
jdpostct.c 10KB
jcmainct.c 10KB
jmemmac.c 10KB
jdapistd.c 9KB
jcapimin.c 9KB
jdatasrc.c 9KB
sai.c 9KB
wrrle.c 9KB
wm8978.c 9KB
rtc.c 9KB
jdatadst.c 9KB
wrppm.c 8KB
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