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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");