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Text File | 1999-01-26 | 12.9 KB | 331 lines

JJJJPPPPEEEEGGGGTTTTRRRRAAAANNNN((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((3333 AAAAuuuugggguuuusssstttt 1111999999997777)))) JJJJPPPPEEEEGGGGTTTTRRRRAAAANNNN((((1111)))) NNNNAAAAMMMMEEEE jpegtran - lossless transformation of JPEG files SSSSYYYYNNNNOOOOPPPPSSSSIIIISSSS jjjjppppeeeeggggttttrrrraaaannnn [ _o_p_t_i_o_n_s ] [ _f_i_l_e_n_a_m_e ] DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN jjjjppppeeeeggggttttrrrraaaannnn performs various useful transformations of JPEG files. It can translate the coded representation from one variant of JPEG to another, for example from baseline JPEG to progressive JPEG or vice versa. It can also perform some rearrangements of the image data, for example turning an image from landscape to portrait format by rotation. jjjjppppeeeeggggttttrrrraaaannnn works by rearranging the compressed data (DCT coefficients), without ever fully decoding the image. Therefore, its transformations are lossless: there is no image degradation at all, which would not be true if you used ddddjjjjppppeeeegggg followed by ccccjjjjppppeeeegggg to accomplish the same conversion. But by the same token, jjjjppppeeeeggggttttrrrraaaannnn cannot perform lossy operations such as changing the image quality. jjjjppppeeeeggggttttrrrraaaannnn reads the named JPEG/JFIF file, or the standard input if no file is named, and produces a JPEG/JFIF file on the standard output. OOOOPPPPTTTTIIIIOOOONNNNSSSS All switch names may be abbreviated; for example, ----ooooppppttttiiiimmmmiiiizzzzeeee may be written ----oooopppptttt or ----oooo. Upper and lower case are equivalent. British spellings are also accepted (e.g., ----ooooppppttttiiiimmmmiiiisssseeee), though for brevity these are not mentioned below. To specify the coded JPEG representation used in the output file, jjjjppppeeeeggggttttrrrraaaannnn accepts a subset of the switches recognized by ccccjjjjppppeeeegggg: ----ooooppppttttiiiimmmmiiiizzzzeeee Perform optimization of entropy encoding parameters. ----pppprrrrooooggggrrrreeeessssssssiiiivvvveeee Create progressive JPEG file. ----rrrreeeessssttttaaaarrrrtttt _N Emit a JPEG restart marker every N MCU rows, or every N MCU blocks if "B" is attached to the number. ----ssssccccaaaannnnssss _f_i_l_e Use the scan script given in the specified text file. See ccccjjjjppppeeeegggg(1) for more details about these switches. If you specify none of these switches, you get a plain baseline- Page 1 (printed 12/16/98) JJJJPPPPEEEEGGGGTTTTRRRRAAAANNNN((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((3333 AAAAuuuugggguuuusssstttt 1111999999997777)))) JJJJPPPPEEEEGGGGTTTTRRRRAAAANNNN((((1111)))) JPEG output file. The quality setting and so forth are determined by the input file. The image can be losslessly transformed by giving one of these switches: ----fffflllliiiipppp hhhhoooorrrriiiizzzzoooonnnnttttaaaallll Mirror image horizontally (left-right). ----fffflllliiiipppp vvvveeeerrrrttttiiiiccccaaaallll Mirror image vertically (top-bottom). ----rrrroooottttaaaatttteeee 99990000 Rotate image 90 degrees clockwise. ----rrrroooottttaaaatttteeee 111188880000 Rotate image 180 degrees. ----rrrroooottttaaaatttteeee 222277770000 Rotate image 270 degrees clockwise (or 90 ccw). ----ttttrrrraaaannnnssssppppoooosssseeee Transpose image (across UL-to-LR axis). ----ttttrrrraaaannnnssssvvvveeeerrrrsssseeee Transverse transpose (across UR-to-LL axis). The transpose transformation has no restrictions regarding image dimensions. The other transformations operate rather oddly if the image dimensions are not a multiple of the iMCU size (usually 8 or 16 pixels), because they can only transform complete blocks of DCT coefficient data in the desired way. jjjjppppeeeeggggttttrrrraaaannnn's default behavior when transforming an odd-size image is designed to preserve exact reversibility and mathematical consistency of the transformation set. As stated, transpose is able to flip the entire image area. Horizontal mirroring leaves any partial iMCU column at the right edge untouched, but is able to flip all rows of the image. Similarly, vertical mirroring leaves any partial iMCU row at the bottom edge untouched, but is able to flip all columns. The other transforms can be built up as sequences of transpose and flip operations; for consistency, their actions on edge pixels are defined to be the same as the end result of the corresponding transpose-and-flip sequence. For practical use, you may prefer to discard any untransformable edge pixels rather than having a strange- looking strip along the right and/or bottom edges of a transformed image. To do this, add the ----ttttrrrriiiimmmm switch: Page 2 (printed 12/16/98) JJJJPPPPEEEEGGGGTTTTRRRRAAAANNNN((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((3333 AAAAuuuugggguuuusssstttt 1111999999997777)))) JJJJPPPPEEEEGGGGTTTTRRRRAAAANNNN((((1111)))) ----ttttrrrriiiimmmm Drop non-transformable edge blocks. Obviously, a transformation with ----ttttrrrriiiimmmm is not reversible, so strictly speaking jjjjppppeeeeggggttttrrrraaaannnn with this switch is not lossless. Also, the expected mathematical equivalences between the transformations no longer hold. For example, ----rrrrooootttt 222277770000 ----ttttrrrriiiimmmm trims only the bottom edge, but ----rrrrooootttt 99990000 ----ttttrrrriiiimmmm followed by ----rrrrooootttt 111188880000 ----ttttrrrriiiimmmm trims both edges. Another not-strictly-lossless transformation switch is: ----ggggrrrraaaayyyyssssccccaaaalllleeee Force grayscale output. This option discards the chrominance channels if the input image is YCbCr (ie, a standard color JPEG), resulting in a grayscale JPEG file. The luminance channel is preserved exactly, so this is a better method of reducing to grayscale than decompression, conversion, and recompression. This switch is particularly handy for fixing a monochrome picture that was mistakenly encoded as a color JPEG. (In such a case, the space savings from getting rid of the near-empty chroma channels won't be large; but the decoding time for a grayscale JPEG is substantially less than that for a color JPEG.) jjjjppppeeeeggggttttrrrraaaannnn also recognizes these switches that control what to do with "extra" markers, such as comment blocks: ----ccccooooppppyyyy nnnnoooonnnneeee Copy no extra markers from source file. This setting suppresses all comments and other excess baggage present in the source file. ----ccccooooppppyyyy ccccoooommmmmmmmeeeennnnttttssss Copy only comment markers. This setting copies comments from the source file, but discards any other inessential data. ----ccccooooppppyyyy aaaallllllll Copy all extra markers. This setting preserves miscellaneous markers found in the source file, such as JFIF thumbnails and Photoshop settings. In some files these extra markers can be sizable. The default behavior is ----ccccooooppppyyyy ccccoooommmmmmmmeeeennnnttttssss. (Note: in IJG releases v6 and v6a, jjjjppppeeeeggggttttrrrraaaannnn always did the equivalent of ----ccccooooppppyyyy nnnnoooonnnneeee.) Additional switches recognized by jpegtran are: Page 3 (printed 12/16/98) JJJJPPPPEEEEGGGGTTTTRRRRAAAANNNN((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((3333 AAAAuuuugggguuuusssstttt 1111999999997777)))) JJJJPPPPEEEEGGGGTTTTRRRRAAAANNNN((((1111)))) ----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. EEEEXXXXAAAAMMMMPPPPLLLLEEEESSSS This example converts a baseline JPEG file to progressive form: jjjjppppeeeeggggttttrrrraaaannnn ----pppprrrrooooggggrrrreeeessssssssiiiivvvveeee _f_o_o._j_p_g >>>> _f_o_o_p_r_o_g._j_p_g This example rotates an image 90 degrees clockwise, discarding any unrotatable edge pixels: jjjjppppeeeeggggttttrrrraaaannnn ----rrrrooootttt 99990000 ----ttttrrrriiiimmmm _f_o_o._j_p_g >>>> _f_o_o_9_0._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 ccccjjjjppppeeeegggg(1), ddddjjjjppppeeeegggg(1), rrrrddddjjjjppppggggccccoooommmm(1), wwwwrrrrjjjjppppggggccccoooommmm(1) 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. The transform options can't transform odd-size images perfectly. Use ----ttttrrrriiiimmmm if you don't like the results without Page 4 (printed 12/16/98) JJJJPPPPEEEEGGGGTTTTRRRRAAAANNNN((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((3333 AAAAuuuugggguuuusssstttt 1111999999997777)))) JJJJPPPPEEEEGGGGTTTTRRRRAAAANNNN((((1111)))) it. The entire image is read into memory and then written out again, even in cases where this isn't really necessary. Expect swapping on large images, especially when using the more complex transform options. Page 5 (printed 12/16/98)