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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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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