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Aminet - June 1993 [Walnut Creek].iso
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amigajpegv4.lha
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cjpeg.man
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1993-01-10
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CCCCJJJJPPPPEEEEGGGG((((1111)))) CCCCJJJJPPPPEEEEGGGG((((1111))))
4444 NNNNoooovvvveeeemmmmbbbbeeeerrrr 1111999999992222
NNNNAAAAMMMMEEEE
cjpeg - compress an image file to a JPEG file
SSSSYYYYNNNNOOOOPPPPSSSSIIIISSSS
ccccjjjjppppeeeegggg [ ----qqqquuuuaaaalllliiiittttyyyy _N ] [ ----ggggrrrraaaayyyyssssccccaaaalllleeee ] [ ----ooooppppttttiiiimmmmiiiizzzzeeee ] [ ----ttttaaaarrrrggggaaaa ] [
----mmmmaaaaxxxxmmmmeeeemmmmoooorrrryyyy _N ] [ ----rrrreeeessssttttaaaarrrrtttt _N ] [ ----ssssmmmmooooooootttthhhh _N ] [ ----vvvveeeerrrrbbbboooosssseeee ] [ ----ddddeeeebbbbuuuugggg ] [
----aaaarrrriiiitttthhhhmmmmeeeettttiiiicccc ] [ ----nnnnooooiiiinnnntttteeeerrrrlllleeeeaaaavvvveeee ] [ ----qqqqttttaaaabbbblllleeeessss _f_i_l_e ] [ ----ssssaaaammmmpppplllleeee _H_x_V[,...] ]
[ _f_i_l_e_n_a_m_e ]
DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN
ccccjjjjppppeeeegggg compresses the named image file, or the standard input if no
file is named, and produces a JPEG/JFIF file on the standard output.
The currently supported input file formats are: PPM (PBMPLUS color
format), PGM (PBMPLUS gray-scale format), GIF, Targa, and RLE (Utah
Raster Toolkit format). (RLE is supported only if the URT library is
available.)
OOOOPPPPTTTTIIIIOOOONNNNSSSS
All switch names may be abbreviated; for example, ----ggggrrrraaaayyyyssssccccaaaalllleeee may be
written ----ggggrrrraaaayyyy or ----ggggrrrr. Most of the "basic" switches can be abbreviated
to as little as one letter. Upper and lower case are equivalent (thus
----GGGGIIIIFFFF is the same as ----ggggiiiiffff). British spellings are also accepted (e.g.,
----ggggrrrreeeeyyyyssssccccaaaalllleeee), though for brevity these are not mentioned below.
The basic switches are:
----qqqquuuuaaaalllliiiittttyyyy _N
Scale quantization tables to adjust image quality. Quality is 0
(worst) to 100 (best); default is 75. (See below for more info.)
----ggggrrrraaaayyyyssssccccaaaalllleeee
Create monochrome JPEG file from color input. Be sure to use
this switch when compressing a grayscale GIF file, because ccccjjjjppppeeeegggg
isn't bright enough to notice whether a GIF file uses only shades
of gray. By saying ----ggggrrrraaaayyyyssssccccaaaalllleeee, you'll get a smaller JPEG file
that takes less time to process.
----ooooppppttttiiiimmmmiiiizzzzeeee
Perform optimization of entropy encoding parameters. Without
this, default encoding parameters are used. ----ooooppppttttiiiimmmmiiiizzzzeeee usually
makes the JPEG file a little smaller, but ccccjjjjppppeeeegggg runs somewhat
slower and needs much more memory. Image quality and speed of
decompression are unaffected by ----ooooppppttttiiiimmmmiiiizzzzeeee.
----ttttaaaarrrrggggaaaa
Input file is Targa format. Targa files that contain an
"identification" field will not be automatically recognized by
ccccjjjjppppeeeegggg; for such files you must specify ----ttttaaaarrrrggggaaaa to make ccccjjjjppppeeeegggg treat
the input as Targa format.
- 1 - Formatted: January 10, 1993
CCCCJJJJPPPPEEEEGGGG((((1111)))) CCCCJJJJPPPPEEEEGGGG((((1111))))
4444 NNNNoooovvvveeeemmmmbbbbeeeerrrr 1111999999992222
The ----qqqquuuuaaaalllliiiittttyyyy switch lets you trade off compressed file size against
quality of the reconstructed image: the higher the quality setting,
the larger the JPEG file, and the closer the output image will be to
the original input. Normally you want to use the lowest quality
setting (smallest file) that decompresses into something visually
indistinguishable from the original image. For this purpose the
quality setting should be between 50 and 95; the default of 75 is
often about right. If you see defects at ----qqqquuuuaaaalllliiiittttyyyy 75, then go up 5 or
10 counts at a time until you are happy with the output image. (The
optimal setting will vary from one image to another.)
----qqqquuuuaaaalllliiiittttyyyy 100 will generate a quantization table of all 1's,
eliminating loss in the quantization step (but there is still
information loss in subsampling, as well as roundoff error). This
setting is mainly of interest for experimental purposes. Quality
values above about 95 are nnnnooootttt recommended for normal use; the
compressed file size goes up dramatically for hardly any gain in
output image quality.
In the other direction, quality values below 50 will produce very
small files of low image quality. Settings around 5 to 10 might be
useful in preparing an index of a large image library, for example.
Try ----qqqquuuuaaaalllliiiittttyyyy 2 (or so) for some amusing Cubist effects. (Note:
quality values below about 25 generate 2-byte quantization tables,
which are considered optional in the JPEG standard. ccccjjjjppppeeeegggg emits a
warning message when you give such a quality value, because some
commercial JPEG programs may be unable to decode the resulting file.)
Switches for advanced users:
----mmmmaaaaxxxxmmmmeeeemmmmoooorrrryyyy _N
Set limit for amount of memory to use in processing large images.
Value is in thousands of bytes, or millions of bytes if "M" is
attached to the number. For example, ----mmmmaaaaxxxx 4444mmmm selects 4000000
bytes. If more space is needed, temporary files will be used.
----rrrreeeessssttttaaaarrrrtttt _N
Emit a JPEG restart marker every N MCU rows, or every N MCU
blocks if "B" is attached to the number. ----rrrreeeessssttttaaaarrrrtttt 0000 (the
default) means no restart markers.
----ssssmmmmooooooootttthhhh _N
Smooth the input image to eliminate dithering noise. N, ranging
from 1 to 100, indicates the strength of smoothing. 0 (the
default) means no smoothing.
----vvvveeeerrrrbbbboooosssseeee
Enable debug printout. More ----vvvv's give more output. Also,
version information is printed at startup.
- 2 - Formatted: January 10, 1993
CCCCJJJJPPPPEEEEGGGG((((1111)))) CCCCJJJJPPPPEEEEGGGG((((1111))))
4444 NNNNoooovvvveeeemmmmbbbbeeeerrrr 1111999999992222
----ddddeeeebbbbuuuugggg
Same as ----vvvveeeerrrrbbbboooosssseeee.
The ----rrrreeeessssttttaaaarrrrtttt option inserts extra markers that allow a JPEG decoder to
resynchronize after a transmission error. Without restart markers,
any damage to a compressed file will usually ruin the image from the
point of the error to the end of the image; with restart markers, the
damage is usually confined to the portion of the image up to the next
restart marker. Of course, the restart markers occupy extra space.
We recommend ----rrrreeeessssttttaaaarrrrtttt 1111 for images that will be transmitted across
unreliable networks such as Usenet.
The ----ssssmmmmooooooootttthhhh option filters the input to eliminate fine-scale noise.
This is often useful when converting GIF files to JPEG: a moderate
smoothing factor of 10 to 50 gets rid of dithering patterns in the
input file, resulting in a smaller JPEG file and a better-looking
image. Too large a smoothing factor will visibly blur the image,
however.
Switches for wizards:
----aaaarrrriiiitttthhhhmmmmeeeettttiiiicccc
Use arithmetic coding rather than Huffman coding. (Not currently
supported for legal reasons.)
----nnnnooooiiiinnnntttteeeerrrrlllleeeeaaaavvvveeee
Generate noninterleaved JPEG file (not yet supported).
----qqqqttttaaaabbbblllleeeessss _f_i_l_e
Use the quantization tables given in the specified file. The
file should contain one to four tables (64 values each) as plain
text. Comments preceded by '#' may be included in the file. The
tables are implicitly numbered 0,1,etc. If ----qqqquuuuaaaalllliiiittttyyyy N is also
specified, the values in the file are scaled according to ccccjjjjppppeeeegggg's
quality scaling curve.
----ssssaaaammmmpppplllleeee _H_x_V[,...]
Set JPEG sampling factors. If you specify fewer H/V pairs than
there are components, the remaining components are set to 1x1
sampling. The default setting is equivalent to ----ssssaaaammmmpppplllleeee 2222xxxx2222.
The "wizard" switches are intended for experimentation with JPEG. If
you don't know what you are doing, ddddoooonnnn''''tttt uuuusssseeee tttthhhheeeemmmm. You can easily
produce files with worse image quality and/or poorer compression than
you'll get from the default settings. Furthermore, these switches
should not be used when making files intended for general use, because
not all JPEG implementations will support unusual JPEG parameter
settings.
EEEEXXXXAAAAMMMMPPPPLLLLEEEESSSS
This example compresses the PPM file foo.ppm with a quality factor of
- 3 - Formatted: January 10, 1993
CCCCJJJJPPPPEEEEGGGG((((1111)))) CCCCJJJJPPPPEEEEGGGG((((1111))))
4444 NNNNoooovvvveeeemmmmbbbbeeeerrrr 1111999999992222
60 and saves the output as foo.jpg:
ccccjjjjppppeeeegggg ----qqqquuuuaaaalllliiiittttyyyy _6_0 _f_o_o._p_p_m >>>> _f_o_o._j_p_g
EEEENNNNVVVVIIIIRRRROOOONNNNMMMMEEEENNNNTTTT
JJJJPPPPEEEEGGGGMMMMEEEEMMMM
If this environment variable is set, its value is the default
memory limit. The value is specified as described for the
----mmmmaaaaxxxxmmmmeeeemmmmoooorrrryyyy switch. JJJJPPPPEEEEGGGGMMMMEEEEMMMM overrides the default value specified
when the program was compiled, and itself is overridden by an
explicit ----mmmmaaaaxxxxmmmmeeeemmmmoooorrrryyyy.
SSSSEEEEEEEE AAAALLLLSSSSOOOO
ddddjjjjppppeeeegggg(1)
ppppppppmmmm(5), ppppggggmmmm(5)
Wallace, Gregory K. "The JPEG Still Picture Compression Standard",
Communications of the ACM, April 1991 (vol. 34, no. 4), pp. 30-44.
AAAAUUUUTTTTHHHHOOOORRRR
Independent JPEG Group
BBBBUUUUGGGGSSSS
Arithmetic coding and interleaved output not yet supported.
Not all variants of Targa file format are supported.
The ----ttttaaaarrrrggggaaaa switch is not a bug, it's a feature. (It would be a bug if
the Targa format designers had not been clueless.)
Still not as fast as we'd like.
- 4 - Formatted: January 10, 1993