SGI Freeware 1999 August

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Text File | 1998-05-21 | 15.4 KB | 332 lines

/xlv1/freeware/1998.May/ghostscript/3.33+jpeg/gs3.33.diffbuild/jpeg-5a CCCCJJJJPPPPEEEEGGGG((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((33330000 AAAAuuuugggguuuusssstttt 1111999999994444)))) CCCCJJJJPPPPEEEEGGGG((((1111)))) NNNNAAAAMMMMEEEE cjpeg - compress an image file to a JPEG file SSSSYYYYNNNNOOOOPPPPSSSSIIIISSSS ccccjjjjppppeeeegggg [ _o_p_t_i_o_n_s ] [ _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), BMP, 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. For most Targa files, you won't need this switch. Page 1 (printed 5/12/98) CCCCJJJJPPPPEEEEGGGG((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((33330000 AAAAuuuugggguuuusssstttt 1111999999994444)))) CCCCJJJJPPPPEEEEGGGG((((1111)))) 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. Use ----bbbbaaaasssseeeelllliiiinnnneeee if you need to ensure compatibility at low quality values.) Switches for advanced users: ----ddddcccctttt iiiinnnntttt Use integer DCT method (default). ----ddddcccctttt ffffaaaasssstttt Use fast integer DCT (less accurate). ----ddddcccctttt ffffllllooooaaaatttt Use floating-point DCT method. The floating-point method is the most accurate, but will be the slowest unless your machine has very fast floating-point hardware. Also note that results of the floating-point method may vary slightly across machines, while the integer methods should give the same results everywhere. The fast integer method is much less accurate than the other two. ----rrrreeeessssttttaaaarrrrtttt _N Page 2 (printed 5/12/98) CCCCJJJJPPPPEEEEGGGG((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((33330000 AAAAuuuugggguuuusssstttt 1111999999994444)))) CCCCJJJJPPPPEEEEGGGG((((1111)))) 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. ----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. ----oooouuuuttttffffiiiilllleeee _n_a_m_e Send output image to the named file, not to standard output. ----vvvveeeerrrrbbbboooosssseeee Enable debug printout. More ----vvvv's give more output. Also, version information is printed at startup. ----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.) ----bbbbaaaasssseeeelllliiiinnnneeee Force a baseline JPEG file to be generated. This Page 3 (printed 5/12/98) CCCCJJJJPPPPEEEEGGGG((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((33330000 AAAAuuuugggguuuusssstttt 1111999999994444)))) CCCCJJJJPPPPEEEEGGGG((((1111)))) clamps quantization values to 8 bits even at low quality settings. ----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. ----qqqqsssslllloooottttssss _N[,...] Select which quantization table to use for each color component. By default, table 0 is used for luminance and table 1 for chrominance components. ----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 60 and saves the output as foo.jpg: ccccjjjjppppeeeegggg ----qqqquuuuaaaalllliiiittttyyyy _6_0 _f_o_o._p_p_m >>>> _f_o_o._j_p_g HHHHIIIINNNNTTTTSSSS Color GIF files are not the ideal input for JPEG; JPEG is really intended for compressing full-color (24-bit) images. In particular, don't try to convert cartoons, line drawings, and other images that have only a few distinct colors. GIF works great on these, JPEG does not. If you want to convert a GIF to JPEG, you should experiment with ccccjjjjppppeeeegggg's ----qqqquuuuaaaalllliiiittttyyyy and ----ssssmmmmooooooootttthhhh options to get a satisfactory conversion. ----ssssmmmmooooooootttthhhh 11110000 or so is often helpful. Avoid running an image through a series of JPEG Page 4 (printed 5/12/98) CCCCJJJJPPPPEEEEGGGG((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((33330000 AAAAuuuugggguuuusssstttt 1111999999994444)))) CCCCJJJJPPPPEEEEGGGG((((1111)))) compression/decompression cycles. Image quality loss will accumulate; after ten or so cycles the image may be noticeably worse than it was after one cycle. It's best to use a lossless format while manipulating an image, then convert to JPEG format when you are ready to file the image away. The ----ooooppppttttiiiimmmmiiiizzzzeeee option to ccccjjjjppppeeeegggg is worth using when you are making a "final" version for posting or archiving. It's also a win when you are using low quality settings to make very small JPEG files; the percentage improvement is often a lot more than it is on larger files. 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), rrrrddddjjjjppppggggccccoooommmm(1), wwwwrrrrjjjjppppggggccccoooommmm(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 is not supported for legal reasons. Not all variants of BMP and Targa file formats 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. Page 5 (printed 5/12/98)