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Diffstat (limited to '3rdparty/libjpeg/cjpeg.1')
| -rw-r--r-- | 3rdparty/libjpeg/cjpeg.1 | 72 |
1 files changed, 60 insertions, 12 deletions
diff --git a/3rdparty/libjpeg/cjpeg.1 b/3rdparty/libjpeg/cjpeg.1 index d50bf80956b..7d685be581a 100644 --- a/3rdparty/libjpeg/cjpeg.1 +++ b/3rdparty/libjpeg/cjpeg.1 @@ -1,4 +1,4 @@ -.TH CJPEG 1 "14 November 2010" +.TH CJPEG 1 "26 July 2015" .SH NAME cjpeg \- compress an image file to a JPEG file .SH SYNOPSIS @@ -16,7 +16,7 @@ cjpeg \- compress an image file to a JPEG file 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, Targa, and RLE (Utah Raster +format), PGM (PBMPLUS grayscale format), BMP, Targa, and RLE (Utah Raster Toolkit format). (RLE is supported only if the URT library is available.) .SH OPTIONS All switch names may be abbreviated; for example, @@ -49,6 +49,17 @@ By saying .BR \-grayscale , you'll get a smaller JPEG file that takes less time to process. .TP +.B \-rgb +Create RGB JPEG file. +Using this switch suppresses the conversion from RGB +colorspace input to the default YCbCr JPEG colorspace. +You can use this switch in combination with the +.BI \-block " N" +switch (see below) for lossless JPEG coding. +See also the +.B \-rgb1 +switch below. +.TP .B \-optimize Perform optimization of entropy encoding parameters. Without this, default encoding parameters are used. @@ -155,6 +166,12 @@ about the same --- often a little smaller. .PP Switches for advanced users: .TP +.B \-arithmetic +Use arithmetic coding. +.B Caution: +arithmetic coded JPEG is not yet widely implemented, so many decoders will +be unable to view an arithmetic coded JPEG file at all. +.TP .BI \-block " N" Set DCT block size. All N from 1 to 16 are possible. Default is 8 (baseline format). @@ -162,9 +179,45 @@ Larger values produce higher compression, smaller values produce higher quality (exact DCT stage possible with 1 or 2; with the default quality of 75 and default Luminance qtable the DCT+Quantization stage is lossless for N=1). -CAUTION: An implementation of the JPEG SmartScale extension is required for -this feature. SmartScale enabled JPEG is not yet widely implemented, so -many decoders will be unable to view a SmartScale extended JPEG file at all. +.B Caution: +An implementation of the JPEG SmartScale extension is required for this +feature. SmartScale enabled JPEG is not yet widely implemented, so many +decoders will be unable to view a SmartScale extended JPEG file at all. +.TP +.B \-rgb1 +Create RGB JPEG file with reversible color transform. +Works like the +.B \-rgb +switch (see above) and inserts a simple reversible color transform +into the processing which significantly improves the compression. +Use this switch in combination with the +.BI \-block " N" +switch (see above) for lossless JPEG coding. +.B Caution: +A decoder with inverse color transform support is required for +this feature. Reversible color transform support is not yet +widely implemented, so many decoders will be unable to view +a reversible color transformed JPEG file at all. +.TP +.B \-bgycc +Create big gamut YCC JPEG file. +In this type of encoding the color difference components are quantized +further by a factor of 2 compared to the normal Cb/Cr values, thus creating +space to allow larger color values with higher saturation than the normal +gamut limits to be encoded. In order to compensate for the loss of color +fidelity compared to a normal YCC encoded file, the color quantization +tables can be adjusted accordingly. For example, +.B cjpeg \-bgycc \-quality +80,90 will give similar results as +.B cjpeg \-quality +80. +.B Caution: +For correct decompression a decoder with big gamut YCC support (JFIF +version 2) is required. An old decoder may or may not display a big +gamut YCC encoded JPEG file, depending on JFIF version check and +corresponding warning/error configuration. In case of a granted +decompression the old decoder will display the image with half +saturated colors. .TP .B \-dct int Use integer DCT method (default). @@ -233,12 +286,6 @@ visibly blur the image, however. .PP Switches for wizards: .TP -.B \-arithmetic -Use arithmetic coding. -.B Caution: -arithmetic coded JPEG is not yet widely implemented, so many decoders will be -unable to view an arithmetic coded JPEG file at all. -.TP .B \-baseline Force baseline-compatible quantization tables to be generated. This clamps quantization values to 8 bits even at low quality settings. (This switch is @@ -328,7 +375,8 @@ Communications of the ACM, April 1991 (vol. 34, no. 4), pp. 30-44. .SH AUTHOR Independent JPEG Group .SH BUGS -GIF input files are no longer supported, to avoid the Unisys LZW patent. +GIF input files are no longer supported, to avoid the Unisys LZW patent +(now expired). (Conversion of GIF files to JPEG is usually a bad idea anyway.) .PP Not all variants of BMP and Targa file formats are supported. |
