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Doc: "MCU block" = "iMCU" or "MCU"

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The JPEG-1 spec never uses the term "MCU block".  That term is rarely
used in other literature to describe the equivalent of an MCU in an
interleaved JPEG image, but the libjpeg documentation uses "iMCU" to
describe the same thing.  "iMCU" is a better term, since the equivalent
of an interleaved MCU can contain multiple DCT blocks (or samples in
lossless mode) that are only grouped together if the image is
interleaved.

In the case of restart markers, "MCU block" was used in the libjpeg
documentation instead of "MCU", but "MCU" is more accurate and less
confusing.  (The restart interval is literally in MCUs, where one MCU
is one data unit in a non-interleaved JPEG image and multiple data units
in a multi-component interleaved JPEG image.)

In the case of 9b704f96b2, the issue was
actually with progressive JPEG images exactly two DCT blocks wide, not
two MCU blocks wide.

This commit also defines "MCU" and "MCU row" in the description of the
various restart marker options/parameters.  Although an MCU row is
technically always a row of samples in lossless mode, "sample row" was
confusing, since it is used in other places to describe a row of samples
for a single component (whereas an MCU row in a typical lossless JPEG
image consists of a row of interleaved samples for all components.)
This commit is contained in:
DRC
2024-08-30 10:50:13 -04:00
parent 5cf7960678
commit 8456d2b98c
23 changed files with 323 additions and 218 deletions
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9
java/TJBench.java
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@@ -797,10 +797,9 @@ final class TJBench {
System.out.println(" default = 8; if N is 16, then -lossless must also be specified]");
System.out.println(" (-precision 12 implies -optimize unless -arithmetic is also specified)");
System.out.println("-quiet = Output results in tabular rather than verbose format");
System.out.println("-restart N = When compressing, add a restart marker every N MCU rows (lossy) or");
System.out.println(" N sample rows (lossless) [default = 0 (no restart markers)]. Append 'B'");
System.out.println(" to specify the restart marker interval in MCU blocks (lossy) or samples");
System.out.println(" (lossless).");
System.out.println("-restart N = When compressing, add a restart marker every N MCU rows");
System.out.println(" [default = 0 (no restart markers)]. Append 'B' to specify the restart");
System.out.println(" marker interval in MCUs (lossy only.)");
System.out.println("-stoponwarning = Immediately discontinue the current");
System.out.println(" compression/decompression/transform operation if a warning (non-fatal");
System.out.println(" error) occurs");
@@ -818,7 +817,7 @@ final class TJBench {
System.out.println(" and H are the width and height of the region (0 = maximum possible width");
System.out.println(" or height) and X and Y are the left and upper boundary of the region, all");
System.out.println(" specified relative to the scaled image dimensions. X must be divible by");
System.out.println(" the scaled MCU width.");
System.out.println(" the scaled iMCU width.");
System.out.println("-fastdct = Use the fastest DCT/IDCT algorithm available");
System.out.println("-fastupsample = Use the fastest chrominance upsampling algorithm available");
System.out.println("-optimize = Compute optimal Huffman tables for JPEG images generated by");

6
java/TJExample.java
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@@ -1,5 +1,5 @@
/*
* Copyright (C)2011-2012, 2014-2015, 2017-2018, 2022-2023 D. R. Commander.
* Copyright (C)2011-2012, 2014-2015, 2017-2018, 2022-2024 D. R. Commander.
* All Rights Reserved.
*
* Redistribution and use in source and binary forms, with or without
@@ -125,8 +125,8 @@ class TJExample implements TJCustomFilter {
System.out.println("-crop WxH+X+Y = Perform lossless cropping on the input image prior to");
System.out.println(" decompressing it. X and Y specify the upper left corner of the cropping");
System.out.println(" region, and W and H specify the width and height of the cropping region.");
System.out.println(" X and Y must be evenly divible by the MCU block size (8x8 if the input");
System.out.println(" image was compressed using no subsampling or grayscale, 16x8 if it was");
System.out.println(" X and Y must be evenly divible by the iMCU size (8x8 if the input image");
System.out.println(" was compressed using no subsampling or grayscale, 16x8 if it was");
System.out.println(" compressed using 4:2:2 subsampling, or 16x16 if it was compressed using");
System.out.println(" 4:2:0 subsampling.)\n");

13
java/doc/index-all.html
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@@ -496,13 +496,11 @@ $('.navPadding').css('padding-top', $('.fixedNav').css("height"));
</dd>
<dt><span class="memberNameLink"><a href="org/libjpegturbo/turbojpeg/TJ.html#getMCUHeight(int)">getMCUHeight(int)</a></span> - Static method in class org.libjpegturbo.turbojpeg.<a href="org/libjpegturbo/turbojpeg/TJ.html" title="class in org.libjpegturbo.turbojpeg">TJ</a></dt>
<dd>
<div class="block">Returns the MCU block height for the given level of chrominance
subsampling.</div>
<div class="block">Returns the iMCU height for the given level of chrominance subsampling.</div>
</dd>
<dt><span class="memberNameLink"><a href="org/libjpegturbo/turbojpeg/TJ.html#getMCUWidth(int)">getMCUWidth(int)</a></span> - Static method in class org.libjpegturbo.turbojpeg.<a href="org/libjpegturbo/turbojpeg/TJ.html" title="class in org.libjpegturbo.turbojpeg">TJ</a></dt>
<dd>
<div class="block">Returns the MCU block width for the given level of chrominance
subsampling.</div>
<div class="block">Returns the iMCU width for the given level of chrominance subsampling.</div>
</dd>
<dt><span class="memberNameLink"><a href="org/libjpegturbo/turbojpeg/TJScalingFactor.html#getNum()">getNum()</a></span> - Method in class org.libjpegturbo.turbojpeg.<a href="org/libjpegturbo/turbojpeg/TJScalingFactor.html" title="class in org.libjpegturbo.turbojpeg">TJScalingFactor</a></dt>
<dd>
@@ -706,7 +704,7 @@ $('.navPadding').css('padding-top', $('.fixedNav').css("height"));
</dd>
<dt><span class="memberNameLink"><a href="org/libjpegturbo/turbojpeg/TJTransform.html#OPT_TRIM">OPT_TRIM</a></span> - Static variable in class org.libjpegturbo.turbojpeg.<a href="org/libjpegturbo/turbojpeg/TJTransform.html" title="class in org.libjpegturbo.turbojpeg">TJTransform</a></dt>
<dd>
<div class="block">Discard any partial MCU blocks that cannot be transformed.</div>
<div class="block">Discard any partial iMCUs that cannot be transformed.</div>
</dd>
<dt><span class="memberNameLink"><a href="org/libjpegturbo/turbojpeg/TJTransform.html#options">options</a></span> - Variable in class org.libjpegturbo.turbojpeg.<a href="org/libjpegturbo/turbojpeg/TJTransform.html" title="class in org.libjpegturbo.turbojpeg">TJTransform</a></dt>
<dd>
@@ -791,12 +789,11 @@ $('.navPadding').css('padding-top', $('.fixedNav').css("height"));
</dd>
<dt><span class="memberNameLink"><a href="org/libjpegturbo/turbojpeg/TJ.html#PARAM_RESTARTBLOCKS">PARAM_RESTARTBLOCKS</a></span> - Static variable in class org.libjpegturbo.turbojpeg.<a href="org/libjpegturbo/turbojpeg/TJ.html" title="class in org.libjpegturbo.turbojpeg">TJ</a></dt>
<dd>
<div class="block">JPEG restart marker interval in MCU blocks [lossy compression only]</div>
<div class="block">JPEG restart marker interval in MCUs [lossy compression only]</div>
</dd>
<dt><span class="memberNameLink"><a href="org/libjpegturbo/turbojpeg/TJ.html#PARAM_RESTARTROWS">PARAM_RESTARTROWS</a></span> - Static variable in class org.libjpegturbo.turbojpeg.<a href="org/libjpegturbo/turbojpeg/TJ.html" title="class in org.libjpegturbo.turbojpeg">TJ</a></dt>
<dd>
<div class="block">JPEG restart marker interval in MCU rows (lossy) or sample rows (lossless)
[compression only]</div>
<div class="block">JPEG restart marker interval in MCU rows [compression only]</div>
</dd>
<dt><span class="memberNameLink"><a href="org/libjpegturbo/turbojpeg/TJ.html#PARAM_SCANLIMIT">PARAM_SCANLIMIT</a></span> - Static variable in class org.libjpegturbo.turbojpeg.<a href="org/libjpegturbo/turbojpeg/TJ.html" title="class in org.libjpegturbo.turbojpeg">TJ</a></dt>
<dd>

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75
java/doc/org/libjpegturbo/turbojpeg/TJ.html
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@@ -417,15 +417,14 @@ extends java.lang.Object</pre>
<td class="colFirst"><code>static int</code></td>
<th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="#PARAM_RESTARTBLOCKS">PARAM_RESTARTBLOCKS</a></span></code></th>
<td class="colLast">
<div class="block">JPEG restart marker interval in MCU blocks [lossy compression only]</div>
<div class="block">JPEG restart marker interval in MCUs [lossy compression only]</div>
</td>
</tr>
<tr class="altColor">
<td class="colFirst"><code>static int</code></td>
<th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="#PARAM_RESTARTROWS">PARAM_RESTARTROWS</a></span></code></th>
<td class="colLast">
<div class="block">JPEG restart marker interval in MCU rows (lossy) or sample rows (lossless)
[compression only]</div>
<div class="block">JPEG restart marker interval in MCU rows [compression only]</div>
</td>
</tr>
<tr class="rowColor">
@@ -687,16 +686,14 @@ extends java.lang.Object</pre>
<td class="colFirst"><code>static int</code></td>
<th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="#getMCUHeight(int)">getMCUHeight</a></span>&#8203;(int&nbsp;subsamp)</code></th>
<td class="colLast">
<div class="block">Returns the MCU block height for the given level of chrominance
subsampling.</div>
<div class="block">Returns the iMCU height for the given level of chrominance subsampling.</div>
</td>
</tr>
<tr id="i6" class="altColor">
<td class="colFirst"><code>static int</code></td>
<th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="#getMCUWidth(int)">getMCUWidth</a></span>&#8203;(int&nbsp;subsamp)</code></th>
<td class="colLast">
<div class="block">Returns the MCU block width for the given level of chrominance
subsampling.</div>
<div class="block">Returns the iMCU width for the given level of chrominance subsampling.</div>
</td>
</tr>
<tr id="i7" class="rowColor">
@@ -1590,8 +1587,8 @@ extends java.lang.Object</pre>
and refined with subsequent higher-quality scans containing
higher-frequency DCT coefficients. When using Huffman entropy coding, the
progressive JPEG format also provides an "end-of-bands (EOB) run" feature
that allows large groups of zeroes, potentially spanning multiple MCU
blocks, to be represented using only a few bytes.
that allows large groups of zeroes, potentially spanning multiple MCUs, to
be represented using only a few bytes.
<p><b>Value</b>
<ul>
@@ -1803,7 +1800,7 @@ extends java.lang.Object</pre>
<li class="blockList">
<h4>PARAM_RESTARTBLOCKS</h4>
<pre>public static final&nbsp;int PARAM_RESTARTBLOCKS</pre>
<div class="block">JPEG restart marker interval in MCU blocks [lossy compression only]
<div class="block">JPEG restart marker interval in MCUs [lossy compression only]
<p>The nature of entropy coding is such that a corrupt JPEG image cannot
be decompressed beyond the point of corruption unless it contains restart
@@ -1813,9 +1810,18 @@ extends java.lang.Object</pre>
tolerance of the JPEG image, but adding too many restart markers can
adversely affect the compression ratio and performance.
<p>In typical JPEG images, an MCU (Minimum Coded Unit) is the minimum set
of interleaved "data units" (8x8 DCT blocks if the image is lossy or
samples if the image is lossless) necessary to represent at least one data
unit per component. (For example, an MCU in an interleaved lossy JPEG
image that uses 4:2:2 subsampling consists of two luminance blocks
followed by one block for each chrominance component.) In
single-component or non-interleaved JPEG images, an MCU is the same as a
data unit.
<p><b>Value</b>
<ul>
<li> the number of MCU blocks between each restart marker <i>[default:
<li> the number of MCUs between each restart marker <i>[default:
<code>0</code> (no restart markers)]</i>
</ul>
@@ -1834,15 +1840,16 @@ extends java.lang.Object</pre>
<li class="blockList">
<h4>PARAM_RESTARTROWS</h4>
<pre>public static final&nbsp;int PARAM_RESTARTROWS</pre>
<div class="block">JPEG restart marker interval in MCU rows (lossy) or sample rows (lossless)
[compression only]
<div class="block">JPEG restart marker interval in MCU rows [compression only]
<p>See <a href="#PARAM_RESTARTBLOCKS"><code>PARAM_RESTARTBLOCKS</code></a> for a description of restart markers.
<p>See <a href="#PARAM_RESTARTBLOCKS"><code>PARAM_RESTARTBLOCKS</code></a> for a description of restart markers
and MCUs. An MCU row is a row of MCUs spanning the entire width of the
image.
<p><b>Value</b>
<ul>
<li> the number of MCU rows or sample rows between each restart marker
<i>[default: <code>0</code> (no restart markers)]</i>
<li> the number of MCU rows between each restart marker <i>[default:
<code>0</code> (no restart markers)]</i>
</ul>
<p>Setting this parameter to a non-zero value sets
@@ -2186,15 +2193,25 @@ public static final&nbsp;int FLAG_LIMITSCANS</pre>
<li class="blockList">
<h4>getMCUWidth</h4>
<pre class="methodSignature">public static&nbsp;int&nbsp;getMCUWidth&#8203;(int&nbsp;subsamp)</pre>
<div class="block">Returns the MCU block width for the given level of chrominance
subsampling.</div>
<div class="block">Returns the iMCU width for the given level of chrominance subsampling.
<p>In a typical lossy JPEG image, 8x8 blocks of DCT coefficients for each
component are interleaved in a single scan. If the image uses chrominance
subsampling, then multiple luminance blocks are stored together, followed
by a single block for each chrominance component. The combination of the
full-resolution luminance block(s) and the (possibly subsampled)
chrominance blocks corresponding to the same pixels is called a "Minimum
Coded Unit" (MCU.) In a non-interleaved lossy JPEG image, each component
is stored in a separate scan, and an MCU is a single DCT block, so we use
the term "iMCU" (interleaved MCU) to refer to the equivalent of an MCU in
an interleaved JPEG image. For the common case of interleaved JPEG
images, an iMCU is the same as an MCU.</div>
<dl>
<dt><span class="paramLabel">Parameters:</span></dt>
<dd><code>subsamp</code> - the level of chrominance subsampling (one of
<a href="#SAMP_444"><code>SAMP_*</code></a>)</dd>
<dt><span class="returnLabel">Returns:</span></dt>
<dd>the MCU block width for the given level of chrominance
subsampling.</dd>
<dd>the iMCU width for the given level of chrominance subsampling.</dd>
</dl>
</li>
</ul>
@@ -2205,15 +2222,25 @@ public static final&nbsp;int FLAG_LIMITSCANS</pre>
<li class="blockList">
<h4>getMCUHeight</h4>
<pre class="methodSignature">public static&nbsp;int&nbsp;getMCUHeight&#8203;(int&nbsp;subsamp)</pre>
<div class="block">Returns the MCU block height for the given level of chrominance
subsampling.</div>
<div class="block">Returns the iMCU height for the given level of chrominance subsampling.
<p>In a typical lossy JPEG image, 8x8 blocks of DCT coefficients for each
component are interleaved in a single scan. If the image uses chrominance
subsampling, then multiple luminance blocks are stored together, followed
by a single block for each chrominance component. The combination of the
full-resolution luminance block(s) and the (possibly subsampled)
chrominance blocks corresponding to the same pixels is called a "Minimum
Coded Unit" (MCU.) In a non-interleaved lossy JPEG image, each component
is stored in a separate scan, and an MCU is a single DCT block, so we use
the term "iMCU" (interleaved MCU) to refer to the equivalent of an MCU in
an interleaved JPEG image. For the common case of interleaved JPEG
images, an iMCU is the same as an MCU.</div>
<dl>
<dt><span class="paramLabel">Parameters:</span></dt>
<dd><code>subsamp</code> - the level of chrominance subsampling (one of
<a href="#SAMP_444"><code>SAMP_*</code></a>)</dd>
<dt><span class="returnLabel">Returns:</span></dt>
<dd>the MCU block height for the given level of chrominance
subsampling.</dd>
<dd>the iMCU height for the given level of chrominance subsampling.</dd>
</dl>
</li>
</ul>

12
java/doc/org/libjpegturbo/turbojpeg/TJDecompressor.html
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@@ -838,8 +838,8 @@ implements java.io.Closeable</pre>
with the JPEG image width and height (see <a href="#getWidth()"><code>getWidth()</code></a> and
<a href="#getHeight()"><code>getHeight()</code></a>.) When decompressing into a planar YUV image, an
intermediate buffer copy will be performed if the width or height of the
scaled destination image is not an even multiple of the MCU block size
(see <a href="TJ.html#getMCUWidth(int)"><code>TJ.getMCUWidth()</code></a> and <a href="TJ.html#getMCUHeight(int)"><code>TJ.getMCUHeight()</code></a>.) Note that decompression scaling is not available
scaled destination image is not an even multiple of the iMCU size (see
<a href="TJ.html#getMCUWidth(int)"><code>TJ.getMCUWidth()</code></a> and <a href="TJ.html#getMCUHeight(int)"><code>TJ.getMCUHeight()</code></a>.) Note that decompression scaling is not available
(and the specified scaling factor is ignored) when decompressing lossless
JPEG images (see <a href="TJ.html#PARAM_LOSSLESS"><code>TJ.PARAM_LOSSLESS</code></a>), since the IDCT algorithm is
not used with those images. Note also that <a href="TJ.html#PARAM_FASTDCT"><code>TJ.PARAM_FASTDCT</code></a> is
@@ -862,10 +862,10 @@ implements java.io.Closeable</pre>
<dd><code>croppingRegion</code> - <code>java.awt.Rectangle</code> instance that
specifies a subregion of the JPEG image to decompress, or
<a href="TJ.html#UNCROPPED"><code>TJ.UNCROPPED</code></a> for no cropping. The left boundary of the cropping
region must be evenly divisible by the scaled MCU block width, which can
be determined by calling <a href="TJScalingFactor.html#getScaled(int)"><code>TJScalingFactor.getScaled()</code></a> with the specified scaling factor (see
<a href="#setScalingFactor(org.libjpegturbo.turbojpeg.TJScalingFactor)"><code>setScalingFactor()</code></a>) and the MCU block width
(see <a href="TJ.html#getMCUWidth(int)"><code>TJ.getMCUWidth()</code></a>) for the level of chrominance
region must be evenly divisible by the scaled iMCU width, which can be
determined by calling <a href="TJScalingFactor.html#getScaled(int)"><code>TJScalingFactor.getScaled()</code></a> with the specified scaling factor (see
<a href="#setScalingFactor(org.libjpegturbo.turbojpeg.TJScalingFactor)"><code>setScalingFactor()</code></a>) and the iMCU width (see
<a href="TJ.html#getMCUWidth(int)"><code>TJ.getMCUWidth()</code></a>) for the level of chrominance
subsampling in the JPEG image (see <a href="TJ.html#PARAM_SUBSAMP"><code>TJ.PARAM_SUBSAMP</code></a>.) The
cropping region should be specified relative to the scaled image
dimensions. Unless <code>croppingRegion</code> is <a href="TJ.html#UNCROPPED"><code>TJ.UNCROPPED</code></a>,

40
java/doc/org/libjpegturbo/turbojpeg/TJTransform.html
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@@ -329,7 +329,7 @@ extends java.awt.Rectangle</pre>
<td class="colFirst"><code>static int</code></td>
<th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="#OPT_TRIM">OPT_TRIM</a></span></code></th>
<td class="colLast">
<div class="block">Discard any partial MCU blocks that cannot be transformed.</div>
<div class="block">Discard any partial iMCUs that cannot be transformed.</div>
</td>
</tr>
<tr class="altColor">
@@ -496,7 +496,7 @@ extends java.awt.Rectangle</pre>
<h4>OP_HFLIP</h4>
<pre>public static final&nbsp;int OP_HFLIP</pre>
<div class="block">Flip (mirror) image horizontally. This transform is imperfect if there
are any partial MCU blocks on the right edge.</div>
are any partial iMCUs on the right edge.</div>
<dl>
<dt><span class="seeLabel">See Also:</span></dt>
<dd><a href="#OPT_PERFECT"><code>OPT_PERFECT</code></a>,
@@ -512,7 +512,7 @@ extends java.awt.Rectangle</pre>
<h4>OP_VFLIP</h4>
<pre>public static final&nbsp;int OP_VFLIP</pre>
<div class="block">Flip (mirror) image vertically. This transform is imperfect if there are
any partial MCU blocks on the bottom edge.</div>
any partial iMCUs on the bottom edge.</div>
<dl>
<dt><span class="seeLabel">See Also:</span></dt>
<dd><a href="#OPT_PERFECT"><code>OPT_PERFECT</code></a>,
@@ -544,8 +544,8 @@ extends java.awt.Rectangle</pre>
<h4>OP_TRANSVERSE</h4>
<pre>public static final&nbsp;int OP_TRANSVERSE</pre>
<div class="block">Transverse transpose image (flip/mirror along upper right to lower left
axis). This transform is imperfect if there are any partial MCU blocks in
the image.</div>
axis). This transform is imperfect if there are any partial iMCUs in the
image.</div>
<dl>
<dt><span class="seeLabel">See Also:</span></dt>
<dd><a href="#OPT_PERFECT"><code>OPT_PERFECT</code></a>,
@@ -561,7 +561,7 @@ extends java.awt.Rectangle</pre>
<h4>OP_ROT90</h4>
<pre>public static final&nbsp;int OP_ROT90</pre>
<div class="block">Rotate image clockwise by 90 degrees. This transform is imperfect if
there are any partial MCU blocks on the bottom edge.</div>
there are any partial iMCUs on the bottom edge.</div>
<dl>
<dt><span class="seeLabel">See Also:</span></dt>
<dd><a href="#OPT_PERFECT"><code>OPT_PERFECT</code></a>,
@@ -577,7 +577,7 @@ extends java.awt.Rectangle</pre>
<h4>OP_ROT180</h4>
<pre>public static final&nbsp;int OP_ROT180</pre>
<div class="block">Rotate image 180 degrees. This transform is imperfect if there are any
partial MCU blocks in the image.</div>
partial iMCUs in the image.</div>
<dl>
<dt><span class="seeLabel">See Also:</span></dt>
<dd><a href="#OPT_PERFECT"><code>OPT_PERFECT</code></a>,
@@ -593,7 +593,7 @@ extends java.awt.Rectangle</pre>
<h4>OP_ROT270</h4>
<pre>public static final&nbsp;int OP_ROT270</pre>
<div class="block">Rotate image counter-clockwise by 90 degrees. This transform is imperfect
if there are any partial MCU blocks on the right edge.</div>
if there are any partial iMCUs on the right edge.</div>
<dl>
<dt><span class="seeLabel">See Also:</span></dt>
<dd><a href="#OPT_PERFECT"><code>OPT_PERFECT</code></a>,
@@ -609,15 +609,15 @@ extends java.awt.Rectangle</pre>
<h4>OPT_PERFECT</h4>
<pre>public static final&nbsp;int OPT_PERFECT</pre>
<div class="block">This option causes <a href="TJTransformer.html#transform(byte%5B%5D%5B%5D,org.libjpegturbo.turbojpeg.TJTransform%5B%5D)"><code>TJTransformer.transform()</code></a> to throw an exception if the transform is not
perfect. Lossless transforms operate on MCU blocks, the size of which
depends on the level of chrominance subsampling used. If the image's
width or height is not evenly divisible by the MCU block size (see
<a href="TJ.html#getMCUWidth(int)"><code>TJ.getMCUWidth()</code></a> and <a href="TJ.html#getMCUHeight(int)"><code>TJ.getMCUHeight()</code></a>), then there will be partial MCU blocks on the right
and/or bottom edges. It is not possible to move these partial MCU blocks
to the top or left of the image, so any transform that would require that
is "imperfect." If this option is not specified, then any partial MCU
blocks that cannot be transformed will be left in place, which will create
odd-looking strips on the right or bottom edge of the image.</div>
perfect. Lossless transforms operate on iMCUs, the size of which depends
on the level of chrominance subsampling used. If the image's width or
height is not evenly divisible by the iMCU size (see <a href="TJ.html#getMCUWidth(int)"><code>TJ.getMCUWidth()</code></a> and <a href="TJ.html#getMCUHeight(int)"><code>TJ.getMCUHeight()</code></a>), then
there will be partial iMCUs on the right and/or bottom edges. It is not
possible to move these partial iMCUs to the top or left of the image, so
any transform that would require that is "imperfect." If this option is
not specified, then any partial iMCUs that cannot be transformed will be
left in place, which will create odd-looking strips on the right or bottom
edge of the image.</div>
<dl>
<dt><span class="seeLabel">See Also:</span></dt>
<dd><a href="../../../constant-values.html#org.libjpegturbo.turbojpeg.TJTransform.OPT_PERFECT">Constant Field Values</a></dd>
@@ -631,7 +631,7 @@ extends java.awt.Rectangle</pre>
<li class="blockList">
<h4>OPT_TRIM</h4>
<pre>public static final&nbsp;int OPT_TRIM</pre>
<div class="block">Discard any partial MCU blocks that cannot be transformed.</div>
<div class="block">Discard any partial iMCUs that cannot be transformed.</div>
<dl>
<dt><span class="seeLabel">See Also:</span></dt>
<dd><a href="../../../constant-values.html#org.libjpegturbo.turbojpeg.TJTransform.OPT_TRIM">Constant Field Values</a></dd>
@@ -818,9 +818,9 @@ extends java.awt.Rectangle</pre>
<dl>
<dt><span class="paramLabel">Parameters:</span></dt>
<dd><code>x</code> - the left boundary of the cropping region. This must be evenly
divisible by the MCU block width (see <a href="TJ.html#getMCUWidth(int)"><code>TJ.getMCUWidth()</code></a>)</dd>
divisible by the iMCU width (see <a href="TJ.html#getMCUWidth(int)"><code>TJ.getMCUWidth()</code></a>)</dd>
<dd><code>y</code> - the upper boundary of the cropping region. This must be evenly
divisible by the MCU block height (see <a href="TJ.html#getMCUHeight(int)"><code>TJ.getMCUHeight()</code></a>)</dd>
divisible by the iMCU height (see <a href="TJ.html#getMCUHeight(int)"><code>TJ.getMCUHeight()</code></a>)</dd>
<dd><code>w</code> - the width of the cropping region. Setting this to 0 is the
equivalent of setting it to (width of the source JPEG image -
<code>x</code>).</dd>

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64
java/org/libjpegturbo/turbojpeg/TJ.java
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@@ -120,14 +120,24 @@ public final class TJ {
public static final int SAMP_UNKNOWN = -1;
/**
* Returns the MCU block width for the given level of chrominance
* subsampling.
* Returns the iMCU width for the given level of chrominance subsampling.
*
* <p>In a typical lossy JPEG image, 8x8 blocks of DCT coefficients for each
* component are interleaved in a single scan. If the image uses chrominance
* subsampling, then multiple luminance blocks are stored together, followed
* by a single block for each chrominance component. The combination of the
* full-resolution luminance block(s) and the (possibly subsampled)
* chrominance blocks corresponding to the same pixels is called a "Minimum
* Coded Unit" (MCU.) In a non-interleaved lossy JPEG image, each component
* is stored in a separate scan, and an MCU is a single DCT block, so we use
* the term "iMCU" (interleaved MCU) to refer to the equivalent of an MCU in
* an interleaved JPEG image. For the common case of interleaved JPEG
* images, an iMCU is the same as an MCU.
*
* @param subsamp the level of chrominance subsampling (one of
* {@link #SAMP_444 SAMP_*})
*
* @return the MCU block width for the given level of chrominance
* subsampling.
* @return the iMCU width for the given level of chrominance subsampling.
*/
public static int getMCUWidth(int subsamp) {
checkSubsampling(subsamp);
@@ -140,14 +150,24 @@ public final class TJ {
/**
* Returns the MCU block height for the given level of chrominance
* subsampling.
* Returns the iMCU height for the given level of chrominance subsampling.
*
* <p>In a typical lossy JPEG image, 8x8 blocks of DCT coefficients for each
* component are interleaved in a single scan. If the image uses chrominance
* subsampling, then multiple luminance blocks are stored together, followed
* by a single block for each chrominance component. The combination of the
* full-resolution luminance block(s) and the (possibly subsampled)
* chrominance blocks corresponding to the same pixels is called a "Minimum
* Coded Unit" (MCU.) In a non-interleaved lossy JPEG image, each component
* is stored in a separate scan, and an MCU is a single DCT block, so we use
* the term "iMCU" (interleaved MCU) to refer to the equivalent of an MCU in
* an interleaved JPEG image. For the common case of interleaved JPEG
* images, an iMCU is the same as an MCU.
*
* @param subsamp the level of chrominance subsampling (one of
* {@link #SAMP_444 SAMP_*})
*
* @return the MCU block height for the given level of chrominance
* subsampling.
* @return the iMCU height for the given level of chrominance subsampling.
*/
public static int getMCUHeight(int subsamp) {
checkSubsampling(subsamp);
@@ -608,8 +628,8 @@ public final class TJ {
* and refined with subsequent higher-quality scans containing
* higher-frequency DCT coefficients. When using Huffman entropy coding, the
* progressive JPEG format also provides an "end-of-bands (EOB) run" feature
* that allows large groups of zeroes, potentially spanning multiple MCU
* blocks, to be represented using only a few bytes.
* that allows large groups of zeroes, potentially spanning multiple MCUs, to
* be represented using only a few bytes.
*
* <p><b>Value</b>
* <ul>
@@ -765,7 +785,7 @@ public final class TJ {
*/
public static final int PARAM_LOSSLESSPT = 17;
/**
* JPEG restart marker interval in MCU blocks [lossy compression only]
* JPEG restart marker interval in MCUs [lossy compression only]
*
* <p>The nature of entropy coding is such that a corrupt JPEG image cannot
* be decompressed beyond the point of corruption unless it contains restart
@@ -775,9 +795,18 @@ public final class TJ {
* tolerance of the JPEG image, but adding too many restart markers can
* adversely affect the compression ratio and performance.
*
* <p>In typical JPEG images, an MCU (Minimum Coded Unit) is the minimum set
* of interleaved "data units" (8x8 DCT blocks if the image is lossy or
* samples if the image is lossless) necessary to represent at least one data
* unit per component. (For example, an MCU in an interleaved lossy JPEG
* image that uses 4:2:2 subsampling consists of two luminance blocks
* followed by one block for each chrominance component.) In
* single-component or non-interleaved JPEG images, an MCU is the same as a
* data unit.
*
* <p><b>Value</b>
* <ul>
* <li> the number of MCU blocks between each restart marker <i>[default:
* <li> the number of MCUs between each restart marker <i>[default:
* <code>0</code> (no restart markers)]</i>
* </ul>
*
@@ -786,15 +815,16 @@ public final class TJ {
*/
public static final int PARAM_RESTARTBLOCKS = 18;
/**
* JPEG restart marker interval in MCU rows (lossy) or sample rows (lossless)
* [compression only]
* JPEG restart marker interval in MCU rows [compression only]
*
* <p>See {@link #PARAM_RESTARTBLOCKS} for a description of restart markers.
* <p>See {@link #PARAM_RESTARTBLOCKS} for a description of restart markers
* and MCUs. An MCU row is a row of MCUs spanning the entire width of the
* image.
*
* <p><b>Value</b>
* <ul>
* <li> the number of MCU rows or sample rows between each restart marker
* <i>[default: <code>0</code> (no restart markers)]</i>
* <li> the number of MCU rows between each restart marker <i>[default:
* <code>0</code> (no restart markers)]</i>
* </ul>
*
* <p>Setting this parameter to a non-zero value sets

12
java/org/libjpegturbo/turbojpeg/TJDecompressor.java
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@@ -222,8 +222,8 @@ public class TJDecompressor implements Closeable {
* with the JPEG image width and height (see {@link #getWidth} and
* {@link #getHeight}.) When decompressing into a planar YUV image, an
* intermediate buffer copy will be performed if the width or height of the
* scaled destination image is not an even multiple of the MCU block size
* (see {@link TJ#getMCUWidth TJ.getMCUWidth()} and {@link TJ#getMCUHeight
* scaled destination image is not an even multiple of the iMCU size (see
* {@link TJ#getMCUWidth TJ.getMCUWidth()} and {@link TJ#getMCUHeight
* TJ.getMCUHeight()}.) Note that decompression scaling is not available
* (and the specified scaling factor is ignored) when decompressing lossless
* JPEG images (see {@link TJ#PARAM_LOSSLESS}), since the IDCT algorithm is
@@ -255,11 +255,11 @@ public class TJDecompressor implements Closeable {
* @param croppingRegion <code>java.awt.Rectangle</code> instance that
* specifies a subregion of the JPEG image to decompress, or
* {@link TJ#UNCROPPED} for no cropping. The left boundary of the cropping
* region must be evenly divisible by the scaled MCU block width, which can
* be determined by calling {@link TJScalingFactor#getScaled
* region must be evenly divisible by the scaled iMCU width, which can be
* determined by calling {@link TJScalingFactor#getScaled
* TJScalingFactor.getScaled()} with the specified scaling factor (see
* {@link #setScalingFactor setScalingFactor()}) and the MCU block width
* (see {@link TJ#getMCUWidth TJ.getMCUWidth()}) for the level of chrominance
* {@link #setScalingFactor setScalingFactor()}) and the iMCU width (see
* {@link TJ#getMCUWidth TJ.getMCUWidth()}) for the level of chrominance
* subsampling in the JPEG image (see {@link TJ#PARAM_SUBSAMP}.) The
* cropping region should be specified relative to the scaled image
* dimensions. Unless <code>croppingRegion</code> is {@link TJ#UNCROPPED},

41
java/org/libjpegturbo/turbojpeg/TJTransform.java
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@@ -48,13 +48,13 @@ public class TJTransform extends Rectangle {
public static final int OP_NONE = 0;
/**
* Flip (mirror) image horizontally. This transform is imperfect if there
* are any partial MCU blocks on the right edge.
* are any partial iMCUs on the right edge.
* @see #OPT_PERFECT
*/
public static final int OP_HFLIP = 1;
/**
* Flip (mirror) image vertically. This transform is imperfect if there are
* any partial MCU blocks on the bottom edge.
* any partial iMCUs on the bottom edge.
* @see #OPT_PERFECT
*/
public static final int OP_VFLIP = 2;
@@ -66,26 +66,26 @@ public class TJTransform extends Rectangle {
public static final int OP_TRANSPOSE = 3;
/**
* Transverse transpose image (flip/mirror along upper right to lower left
* axis). This transform is imperfect if there are any partial MCU blocks in
* the image.
* axis). This transform is imperfect if there are any partial iMCUs in the
* image.
* @see #OPT_PERFECT
*/
public static final int OP_TRANSVERSE = 4;
/**
* Rotate image clockwise by 90 degrees. This transform is imperfect if
* there are any partial MCU blocks on the bottom edge.
* there are any partial iMCUs on the bottom edge.
* @see #OPT_PERFECT
*/
public static final int OP_ROT90 = 5;
/**
* Rotate image 180 degrees. This transform is imperfect if there are any
* partial MCU blocks in the image.
* partial iMCUs in the image.
* @see #OPT_PERFECT
*/
public static final int OP_ROT180 = 6;
/**
* Rotate image counter-clockwise by 90 degrees. This transform is imperfect
* if there are any partial MCU blocks on the right edge.
* if there are any partial iMCUs on the right edge.
* @see #OPT_PERFECT
*/
public static final int OP_ROT270 = 7;
@@ -94,20 +94,20 @@ public class TJTransform extends Rectangle {
/**
* This option causes {@link TJTransformer#transform
* TJTransformer.transform()} to throw an exception if the transform is not
* perfect. Lossless transforms operate on MCU blocks, the size of which
* depends on the level of chrominance subsampling used. If the image's
* width or height is not evenly divisible by the MCU block size (see
* {@link TJ#getMCUWidth TJ.getMCUWidth()} and {@link TJ#getMCUHeight
* TJ.getMCUHeight()}), then there will be partial MCU blocks on the right
* and/or bottom edges. It is not possible to move these partial MCU blocks
* to the top or left of the image, so any transform that would require that
* is "imperfect." If this option is not specified, then any partial MCU
* blocks that cannot be transformed will be left in place, which will create
* odd-looking strips on the right or bottom edge of the image.
* perfect. Lossless transforms operate on iMCUs, the size of which depends
* on the level of chrominance subsampling used. If the image's width or
* height is not evenly divisible by the iMCU size (see {@link TJ#getMCUWidth
* TJ.getMCUWidth()} and {@link TJ#getMCUHeight TJ.getMCUHeight()}), then
* there will be partial iMCUs on the right and/or bottom edges. It is not
* possible to move these partial iMCUs to the top or left of the image, so
* any transform that would require that is "imperfect." If this option is
* not specified, then any partial iMCUs that cannot be transformed will be
* left in place, which will create odd-looking strips on the right or bottom
* edge of the image.
*/
public static final int OPT_PERFECT = (1 << 0);
/**
* Discard any partial MCU blocks that cannot be transformed.
* Discard any partial iMCUs that cannot be transformed.
*/
public static final int OPT_TRIM = (1 << 1);
/**
@@ -164,11 +164,10 @@ public class TJTransform extends Rectangle {
* Create a new lossless transform instance with the given parameters.
*
* @param x the left boundary of the cropping region. This must be evenly
* divisible by the MCU block width (see {@link TJ#getMCUWidth
* TJ.getMCUWidth()})
* divisible by the iMCU width (see {@link TJ#getMCUWidth TJ.getMCUWidth()})
*
* @param y the upper boundary of the cropping region. This must be evenly
* divisible by the MCU block height (see {@link TJ#getMCUHeight
* divisible by the iMCU height (see {@link TJ#getMCUHeight
* TJ.getMCUHeight()})
*
* @param w the width of the cropping region. Setting this to 0 is the