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JPEG_SOFT_LIB_2007.12.17.rar_2007 （902个子文件）

cjpeg.1 10KB

jpegtran.1 8KB

djpeg.1 7KB

wrjpgcom.1 3KB

rdjpgcom.1 2KB

ansi2knr.1 2KB

libjpeg.a 3.07MB

libjpeg.a 3.05MB

makefile.ansi 12KB

jmemdosa.asm 8KB

makefile.bcc 14KB

jconfig.bcc 1KB

testimg.bmp 34KB

jquant2.c 49KB

jdmarker.c 41KB

jmemmgr.c 41KB

transupp.c 33KB

jquant1.c 31KB

jchuff.c 28KB

jcphuff.c 25KB

jdcoefct.c 25KB

example.c 25KB

ansi2knr.c 22KB

jcparam.c 21KB

jdhuff.c 21KB

jdphuff.c 21KB

jdmainct.c 20KB

cjpeg.c 20KB

jcmaster.c 20KB

jdmaster.c 20KB

djpeg.c 20KB

jmemdos.c 19KB

jcsample.c 19KB

jcmarker.c 17KB

wrjpgcom.c 17KB

jdsample.c 16KB

jccoefct.c 16KB

jpegtran.c 16KB

rdtarga.c 15KB

jccolor.c 15KB

jidctint.c 15KB

rdppm.c 14KB

rdjpgcom.c 14KB

jctrans.c 14KB

wrbmp.c 14KB

jdmerge.c 14KB

rdbmp.c 14KB

jidctred.c 14KB

jdinput.c 14KB

jdcolor.c 13KB

jidctfst.c 13KB

共 902 条

USING THE IJG JPEG LIBRARY

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

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

* Arithmetic entropy coding (unsupported for legal reasons)

* DNL marker

* Nonintegral subsampling ratios

We support both 8- and 12-bit data precision, but this is a compile-time

choice rather than a run-time choice; hence it is difficult to use both

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

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

------------

Before diving into procedural details, it is helpful to understand the

image data format that the JPEG library expects or returns.

The standard input image format is a rectangular array of pixels, with

each

pixel having the same number of "component" or "sample" values (color

channels). You must specify how many components there are and the

colorspace

interpretation of the components. Most applications will use RGB data

(three components per pixel) or grayscale data (one component per pixel).

PLEASE NOTE THAT RGB DATA IS THREE SAMPLES PER PIXEL, GRAYSCALE ONLY ONE.

A remarkable number of people manage to miss this, only to find that their

programs don't work with grayscale JPEG files.

There is no provision for colormapped input. JPEG files are always full-

color

or full grayscale (or sometimes another colorspace such as CMYK). You can

feed in a colormapped image by expanding it to full-color format. However

JPEG often doesn't work very well with source data that has been

colormapped,

because of dithering noise. This is discussed in more detail in the JPEG

FAQ

and the other references mentioned in the README file.

Pixels are stored by scanlines, with each scanline running from left to

right. The component values for each pixel are adjacent in the row; for

example, R,G,B,R,G,B,R,G,B,... for 24-bit RGB color. Each scanline is an

array of data type JSAMPLE --- which is typically "unsigned char", unless

you've changed jmorecfg.h. (You can also change the RGB pixel layout, say

to B,G,R order, by modifying jmorecfg.h. But see the restrictions listed

that file before doing so.)

A 2-D array of pixels is formed by making a list of pointers to the starts

scanlines; so the scanlines need not be physically adjacent in memory.

Even

if you process just one scanline at a time, you must make a one-element

pointer array to conform to this structure. Pointers to JSAMPLE rows are

type JSAMPROW, and the pointer to the pointer array is of type JSAMPARRAY.

The library accepts or supplies one or more complete scanlines per call.

It is not possible to process part of a row at a time. Scanlines are

always

processed top-to-bottom. You can process an entire image in one call if

you

have it all in memory, but usually it's simplest to process one scanline

a time.

For best results, source data values should have the precision specified

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