Changeset 283 for trunk/libjpeg/cjpeg.1


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Timestamp:
Jan 4, 2010, 8:20:18 PM (12 years ago)
Author:
rbri
Message:

JPEG plugin: libjpeg updated to version 7

File:
1 edited

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  • trunk/libjpeg/cjpeg.1

    r15 r283  
    1 .TH CJPEG 1 "20 March 1998"
     1.TH CJPEG 1 "10 June 2009"
    22.SH NAME
    33cjpeg \- compress an image file to a JPEG file
     
    3737The basic switches are:
    3838.TP
    39 .BI \-quality " N"
     39.BI \-quality " N[,...]"
    4040Scale quantization tables to adjust image quality.  Quality is 0 (worst) to
    4141100 (best); default is 75.  (See below for more info.)
     
    6262.B \-progressive
    6363Create progressive JPEG file (see below).
     64.TP
     65.BI \-scale " M/N"
     66Scale the output image by a factor M/N.  Currently supported scale factors are
     678/N with all N from 1 to 16.
    6468.TP
    6569.B \-targa
     
    108112.B \-baseline
    109113if you need to ensure compatibility at low quality values.)
     114.PP
     115The
     116.B \-quality
     117option has been extended in IJG version 7 for support of separate quality
     118settings for luminance and chrominance (or in general, for every provided
     119quantization table slot).  This feature is useful for high-quality
     120applications which cannot accept the damage of color data by coarse
     121subsampling settings.  You can now easily reduce the color data amount more
     122smoothly with finer control without separate subsampling.  The resulting file
     123is fully compliant with standard JPEG decoders.
     124Note that the
     125.B \-quality
     126ratings refer to the quantization table slots, and that the last value is
     127replicated if there are more q-table slots than parameters.  The default
     128q-table slots are 0 for luminance and 1 for chrominance with default tables as
     129given in the JPEG standard.  This is compatible with the old behaviour in case
     130that only one parameter is given, which is then used for both luminance and
     131chrominance (slots 0 and 1).  More or custom quantization tables can be set
     132with
     133.B \-qtables
     134and assigned to components with
     135.B \-qslots
     136parameter (see the "wizard" switches below).
     137.B Caution:
     138You must explicitely add
     139.BI \-sample " 1x1"
     140for efficient separate color
     141quality selection, since the default value used by library is 2x2!
    110142.PP
    111143The
     
    118150standard JPEG file of the same quality setting, and the total file size is
    119151about the same --- often a little smaller.
    120 .B Caution:
    121 progressive JPEG is not yet widely implemented, so many decoders will be
    122 unable to view a progressive JPEG file at all.
    123152.PP
    124153Switches for advanced users:
     
    137166machines, while the integer methods should give the same results everywhere.
    138167The fast integer method is much less accurate than the other two.
     168.TP
     169.B \-nosmooth
     170Don't use high-quality downsampling.
    139171.TP
    140172.BI \-restart " N"
     
    188220Switches for wizards:
    189221.TP
     222.B \-arithmetic
     223Use arithmetic coding.
     224.B Caution:
     225arithmetic coded JPEG is not yet widely implemented, so many decoders will be
     226unable to view an arithmetic coded JPEG file at all.
     227.TP
    190228.B \-baseline
    191229Force baseline-compatible quantization tables to be generated.  This clamps
     
    212250The "wizard" switches are intended for experimentation with JPEG.  If you
    213251don't know what you are doing, \fBdon't use them\fR.  These switches are
    214 documented further in the file wizard.doc.
     252documented further in the file wizard.txt.
    215253.SH EXAMPLES
    216254.LP
     
    277315Independent JPEG Group
    278316.SH BUGS
    279 Arithmetic coding is not supported for legal reasons.
    280 .PP
    281317GIF input files are no longer supported, to avoid the Unisys LZW patent.
    282 Use a Unisys-licensed program if you need to read a GIF file.  (Conversion
    283 of GIF files to JPEG is usually a bad idea anyway.)
     318(Conversion of GIF files to JPEG is usually a bad idea anyway.)
    284319.PP
    285320Not all variants of BMP and Targa file formats are supported.
     
    289324switch is not a bug, it's a feature.  (It would be a bug if the Targa format
    290325designers had not been clueless.)
    291 .PP
    292 Still not as fast as we'd like.
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