+++ /dev/null
-.TH CJPEG 1 "20 March 1998"
-.SH NAME
-cjpeg \- compress an image file to a JPEG file
-.SH SYNOPSIS
-.B cjpeg
-[
-.I options
-]
-[
-.I filename
-]
-.LP
-.SH DESCRIPTION
-.LP
-.B cjpeg
-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
-Toolkit format). (RLE is supported only if the URT library is available.)
-.SH OPTIONS
-All switch names may be abbreviated; for example,
-.B \-grayscale
-may be written
-.B \-gray
-or
-.BR \-gr .
-Most of the "basic" switches can be abbreviated to as little as one letter.
-Upper and lower case are equivalent (thus
-.B \-BMP
-is the same as
-.BR \-bmp ).
-British spellings are also accepted (e.g.,
-.BR \-greyscale ),
-though for brevity these are not mentioned below.
-.PP
-The basic switches are:
-.TP
-.BI \-quality " N"
-Scale quantization tables to adjust image quality. Quality is 0 (worst) to
-100 (best); default is 75. (See below for more info.)
-.TP
-.B \-grayscale
-Create monochrome JPEG file from color input. Be sure to use this switch when
-compressing a grayscale BMP file, because
-.B cjpeg
-isn't bright enough to notice whether a BMP file uses only shades of gray.
-By saying
-.BR \-grayscale ,
-you'll get a smaller JPEG file that takes less time to process.
-.TP
-.B \-optimize
-Perform optimization of entropy encoding parameters. Without this, default
-encoding parameters are used.
-.B \-optimize
-usually makes the JPEG file a little smaller, but
-.B cjpeg
-runs somewhat slower and needs much more memory. Image quality and speed of
-decompression are unaffected by
-.BR \-optimize .
-.TP
-.B \-progressive
-Create progressive JPEG file (see below).
-.TP
-.B \-targa
-Input file is Targa format. Targa files that contain an "identification"
-field will not be automatically recognized by
-.BR cjpeg ;
-for such files you must specify
-.B \-targa
-to make
-.B cjpeg
-treat the input as Targa format.
-For most Targa files, you won't need this switch.
-.PP
-The
-.B \-quality
-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
-.B \-quality
-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.)
-.PP
-.B \-quality
-100 will generate a quantization table of all 1's, minimizing 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
-.B not
-recommended for normal use; the compressed file size goes up dramatically for
-hardly any gain in output image quality.
-.PP
-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
-.B \-quality
-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.
-.B cjpeg
-emits a warning message when you give such a quality value, because some
-other JPEG programs may be unable to decode the resulting file. Use
-.B \-baseline
-if you need to ensure compatibility at low quality values.)
-.PP
-The
-.B \-progressive
-switch creates a "progressive JPEG" file. In this type of JPEG file, the data
-is stored in multiple scans of increasing quality. If the file is being
-transmitted over a slow communications link, the decoder can use the first
-scan to display a low-quality image very quickly, and can then improve the
-display with each subsequent scan. The final image is exactly equivalent to a
-standard JPEG file of the same quality setting, and the total file size is
-about the same --- often a little smaller.
-.B Caution:
-progressive JPEG is not yet widely implemented, so many decoders will be
-unable to view a progressive JPEG file at all.
-.PP
-Switches for advanced users:
-.TP
-.B \-dct int
-Use integer DCT method (default).
-.TP
-.B \-dct fast
-Use fast integer DCT (less accurate).
-.TP
-.B \-dct float
-Use floating-point DCT method.
-The float method is very slightly more accurate than the int method, but is
-much slower 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.
-.TP
-.BI \-restart " N"
-Emit a JPEG restart marker every N MCU rows, or every N MCU blocks if "B" is
-attached to the number.
-.B \-restart 0
-(the default) means no restart markers.
-.TP
-.BI \-smooth " 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.
-.TP
-.BI \-maxmemory " 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,
-.B \-max 4m
-selects 4000000 bytes. If more space is needed, temporary files will be used.
-.TP
-.BI \-outfile " name"
-Send output image to the named file, not to standard output.
-.TP
-.B \-verbose
-Enable debug printout. More
-.BR \-v 's
-give more output. Also, version information is printed at startup.
-.TP
-.B \-debug
-Same as
-.BR \-verbose .
-.PP
-The
-.B \-restart
-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
-.B \-restart 1
-for images that will be transmitted across unreliable networks such as Usenet.
-.PP
-The
-.B \-smooth
-option filters the input to eliminate fine-scale noise. This is often useful
-when converting dithered images 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.
-.PP
-Switches for wizards:
-.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
-poorly named, since it does not ensure that the output is actually baseline
-JPEG. For example, you can use
-.B \-baseline
-and
-.B \-progressive
-together.)
-.TP
-.BI \-qtables " file"
-Use the quantization tables given in the specified text file.
-.TP
-.BI \-qslots " N[,...]"
-Select which quantization table to use for each color component.
-.TP
-.BI \-sample " HxV[,...]"
-Set JPEG sampling factors for each color component.
-.TP
-.BI \-scans " file"
-Use the scan script given in the specified text file.
-.PP
-The "wizard" switches are intended for experimentation with JPEG. If you
-don't know what you are doing, \fBdon't use them\fR. These switches are
-documented further in the file wizard.doc.
-.SH EXAMPLES
-.LP
-This example compresses the PPM file foo.ppm with a quality factor of
-60 and saves the output as foo.jpg:
-.IP
-.B cjpeg \-quality
-.I 60 foo.ppm
-.B >
-.I foo.jpg
-.SH HINTS
-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
-.BR cjpeg 's
-.B \-quality
-and
-.B \-smooth
-options to get a satisfactory conversion.
-.B \-smooth 10
-or so is often helpful.
-.PP
-Avoid running an image through a series of JPEG 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.
-.PP
-The
-.B \-optimize
-option to
-.B cjpeg
-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. (At present,
-.B \-optimize
-mode is always selected when generating progressive JPEG files.)
-.SH ENVIRONMENT
-.TP
-.B JPEGMEM
-If this environment variable is set, its value is the default memory limit.
-The value is specified as described for the
-.B \-maxmemory
-switch.
-.B JPEGMEM
-overrides the default value specified when the program was compiled, and
-itself is overridden by an explicit
-.BR \-maxmemory .
-.SH SEE ALSO
-.BR djpeg (1),
-.BR jpegtran (1),
-.BR rdjpgcom (1),
-.BR wrjpgcom (1)
-.br
-.BR ppm (5),
-.BR pgm (5)
-.br
-Wallace, Gregory K. "The JPEG Still Picture Compression Standard",
-Communications of the ACM, April 1991 (vol. 34, no. 4), pp. 30-44.
-.SH AUTHOR
-Independent JPEG Group
-.SH BUGS
-Arithmetic coding is not supported for legal reasons.
-.PP
-GIF input files are no longer supported, to avoid the Unisys LZW patent.
-Use a Unisys-licensed program if you need to read a GIF file. (Conversion
-of GIF files to JPEG is usually a bad idea anyway.)
-.PP
-Not all variants of BMP and Targa file formats are supported.
-.PP
-The
-.B \-targa
-switch is not a bug, it's a feature. (It would be a bug if the Targa format
-designers had not been clueless.)
-.PP
-Still not as fast as we'd like.
projects / synfig.git / blobdiff