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Incorporate a few upstream doc changes; grammar police; wordsmithing; Move -arithmetic into "switches for advanced users"; Additional documentation for IDCT scaling extensions

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git-svn-id: svn+ssh://svn.code.sf.net/p/libjpeg-turbo/code/trunk@765 632fc199-4ca6-4c93-a231-07263d6284db
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DRC
2012-01-31 10:19:29 +00:00
parent 7ab0364a37 5829cb2398
commit 66a69f04c6
6 changed files with 37 additions and 34 deletions
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13
README
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@@ -1,7 +1,8 @@
libjpeg-turbo note: This file is mostly taken from the libjpeg README
file, and it is included only for reference. Some parts of it may not apply to
libjpeg-turbo. Please see README-turbo.txt for information specific to the
turbo version.
libjpeg-turbo note: This file contains portions of the libjpeg v6b and v8
README files, with additional wordsmithing by The libjpeg-turbo Project.
It is included only for reference, as some parts of it may not apply to
libjpeg-turbo. Please see README-turbo.txt for information specific to
libjpeg-turbo.
The Independent JPEG Group's JPEG software
@@ -256,8 +257,8 @@ ARCHIVE LOCATIONS
The "official" archive site for this software is www.ijg.org.
The most recent released version can always be found there in
directory "files". This particular version will be archived as
http://www.ijg.org/files/jpegsrc.v8b.tar.gz, and in Windows-compatible
"zip" archive format as http://www.ijg.org/files/jpegsr8b.zip.
http://www.ijg.org/files/jpegsrc.v8d.tar.gz, and in Windows-compatible
"zip" archive format as http://www.ijg.org/files/jpegsr8d.zip.
The JPEG FAQ (Frequently Asked Questions) article is a source of some
general information about JPEG.

4
cjpeg.1
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@@ -1,4 +1,4 @@
.TH CJPEG 1 "27 January 2012"
.TH CJPEG 1 "31 January 2012"
.SH NAME
cjpeg \- compress an image file to a JPEG file
.SH SYNOPSIS
@@ -121,7 +121,7 @@ quality-sensitive applications, for which the artifacts generated by
subsampling may be unacceptable.
.PP
The \fB-quality\fR option accepts a comma-separated list of parameters, which
respectively refer to the quality levels which should be assigned to the
respectively refer to the quality levels that should be assigned to the
quantization table slots. If there are more q-table slots than parameters,
then the last parameter is replicated. Thus, if only one quality parameter is
given, this is used for both luminance and chrominance (slots 0 and 1,

4
jpegtran.1
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@@ -1,4 +1,4 @@
.TH JPEGTRAN 1 "11 October 2010"
.TH JPEGTRAN 1 "31 January 2012"
.SH NAME
jpegtran \- lossless transformation of JPEG files
.SH SYNOPSIS
@@ -184,7 +184,7 @@ comments and other excess baggage present in the source file.
.TP
.B \-copy comments
Copy only comment markers. This setting copies comments from the source file
but discards any other data which is inessential for image display.
but discards any other data that is inessential for image display.
.TP
.B \-copy all
Copy all extra markers. This setting preserves miscellaneous markers

5
libjpeg.txt
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@@ -983,7 +983,7 @@ int q_scale_factor[NUM_QUANT_TBLS]
See rdswitch.c and cjpeg.c for an example of usage.
Note that the q_scale_factor[] values use "linear" scales, so JPEG
quality levels chosen by the user must be converted to these scales
using jpeg_quality_scaling(). Here is an example which corresponds to
using jpeg_quality_scaling(). Here is an example that corresponds to
cjpeg -quality 90,70:
jpeg_set_defaults(cinfo);
@@ -1019,7 +1019,8 @@ The actual dimensions of the JPEG image that will be written to the file are
given by the following fields. These are computed from the input image
dimensions and the compression parameters by jpeg_start_compress(). You can
also call jpeg_calc_jpeg_dimensions() to obtain the values that will result
from the current parameter settings.
from the current parameter settings. This can be useful if you are trying
to pick a scaling ratio that will get close to a desired target size.
JDIMENSION jpeg_width Actual dimensions of output image.
JDIMENSION jpeg_height

20
structure.txt
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@@ -1,6 +1,6 @@
IJG JPEG LIBRARY: SYSTEM ARCHITECTURE
Copyright (C) 1991-2009, Thomas G. Lane, Guido Vollbeding.
Copyright (C) 1991-2012, 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.
@@ -385,8 +385,9 @@ objects:
* Data destination manager: writes the output JPEG datastream to its final
destination (e.g., a file). The destination manager supplied with the
library knows how to write to a stdio stream; for other behaviors, the
surrounding application may provide its own destination manager.
library knows how to write to a stdio stream or to a memory buffer;
for other behaviors, the surrounding application may provide its own
destination manager.
* Memory manager: allocates and releases memory, controls virtual arrays
(with backing store management, where required).
@@ -454,8 +455,8 @@ shown are:
buffered by the coefficient controller have NOT been dequantized; we
merge dequantization and inverse DCT into a single step for speed reasons.
When scaled-down output is asked for, simplified DCT algorithms may be used
that emit only 1x1, 2x2, or 4x4 samples per DCT block, not the full 8x8.
Works on one DCT block at a time.
that emit fewer samples per DCT block, not the full 8x8. Works on one DCT
block at a time.
* Postprocessing controller: buffer controller for the color quantization
input buffer, when quantization is in use. (Without quantization, this
@@ -504,9 +505,9 @@ objects:
* Marker reading: decodes JPEG markers (except for RSTn).
* Data source manager: supplies the input JPEG datastream. The source
manager supplied with the library knows how to read from a stdio stream;
for other behaviors, the surrounding application may provide its own source
manager.
manager supplied with the library knows how to read from a stdio stream
or from a memory buffer; for other behaviors, the surrounding application
may provide its own source manager.
* Memory manager: same as for compression library.
@@ -586,8 +587,7 @@ as "((value) & 0xFF)" on signed-char machines and "((int) (value))" elsewhere.
With these conventions, JSAMPLE values can be assumed to be >= 0. This helps
simplify correct rounding during downsampling, etc. The JPEG standard's
specification that sample values run from -128..127 is accommodated by
subtracting 128 just as the sample value is copied into the source array for
the DCT step (this will be an array of signed ints). Similarly, during
subtracting 128 from the sample value in the DCT step. Similarly, during
decompression the output of the IDCT step will be immediately shifted back to
0..255. (NB: different values are required when 12-bit samples are in use.
The code is written in terms of MAXJSAMPLE and CENTERJSAMPLE, which will be

25
usage.txt
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@@ -131,7 +131,7 @@ quality-sensitive applications, for which the artifacts generated by
subsampling may be unacceptable.
The -quality option accepts a comma-separated list of parameters, which
respectively refer to the quality levels which should be assigned to the
respectively refer to the quality levels that should be assigned to the
quantization table slots. If there are more q-table slots than parameters,
then the last parameter is replicated. Thus, if only one quality parameter is
given, this is used for both luminance and chrominance (slots 0 and 1,
@@ -157,6 +157,11 @@ file size is about the same --- often a little smaller.
Switches for advanced users:
-arithmetic Use arithmetic coding. CAUTION: arithmetic coded JPEG
is not yet widely implemented, so many decoders will
be unable to view an arithmetic coded JPEG file at
all.
-dct int Use integer DCT method (default).
-dct fast Use fast integer DCT (less accurate).
-dct float Use floating-point DCT method.
@@ -201,11 +206,6 @@ factor will visibly blur the image, however.
Switches for wizards:
-arithmetic Use arithmetic coding. CAUTION: arithmetic coded JPEG
is not yet widely implemented, so many decoders will
be unable to view an arithmetic coded JPEG file at
all.
-baseline Force baseline-compatible quantization tables to be
generated. This clamps quantization values to 8 bits
even at low quality settings. (This switch is poorly
@@ -250,10 +250,11 @@ The basic command line switches for djpeg are:
djpeg runs noticeably faster in this mode.
-scale M/N Scale the output image by a factor M/N. Currently
the scale factor must be 1/1, 1/2, 1/4, or 1/8.
Scaling is handy if the image is larger than your
screen; also, djpeg runs much faster when scaling
down the output.
the scale factor must be M/8, where M is an integer
between 1 and 16 inclusive, or any reduced fraction
thereof (such as 1/2, 3/4, etc. Scaling is handy if
the image is larger than your screen; also, djpeg runs
much faster when scaling down the output.
-bmp Select BMP output format (Windows flavor). 8-bit
colormapped format is emitted if -colors or -grayscale
@@ -447,9 +448,9 @@ To specify the coded JPEG representation used in the output file,
jpegtran accepts a subset of the switches recognized by cjpeg:
-optimize Perform optimization of entropy encoding parameters.
-progressive Create progressive JPEG file.
-arithmetic Use arithmetic coding.
-restart N Emit a JPEG restart marker every N MCU rows, or every
N MCU blocks if "B" is attached to the number.
-arithmetic Use arithmetic coding.
-scans file Use the scan script given in the specified text file.
See the previous discussion of cjpeg for more details about these switches.
If you specify none of these switches, you get a plain baseline-JPEG output
@@ -527,7 +528,7 @@ markers, such as comment blocks:
present in the source file.
-copy comments Copy only comment markers. This setting copies
comments from the source file but discards
any other data which is inessential for image display.
any other data that is inessential for image display.
-copy all Copy all extra markers. This setting preserves
miscellaneous markers found in the source file, such
as JFIF thumbnails, Exif data, and Photoshop settings.