'\" te
.TH cjpeg 1 "26 Mar 2004" "SunOS 5.11" "User Commands"
.SH "NAME"
cjpeg \- compress
an image file to a JPEG file
.SH "SYNOPSIS"
.PP
\fBcjpeg\fR [\fB\fIoptions\fR\fR] [\fB\fIfilename\fR\fR]
.SH "DESCRIPTION"
.PP
\fBcjpeg\fR 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 following input file formats are currently supported:
.sp
.in +2
\(bu
.mk
.in +3
.rt
BMP
.sp
.in -3
\(bu
.mk
.in +3
.rt
PGM, the PBMPLUS gray-scale format
.sp
.in -3
\(bu
.mk
.in +3
.rt
PPM, the PBMPLUS color format
.sp
.in -3
\(bu
.mk
.in +3
.rt
RLE, the Utah Raster Toolkit format
.sp
.in -3
\(bu
.mk
.in +3
.rt
Targa
.sp
.in -3
.in -2
.PP
RLE is supported only if the URT library is available\&.
.SH "OPTIONS"
.PP
All options may be abbreviated\&. For example, -\fBgrayscale\fR
may be written -\fBgray\fR or -\fBgr\fR\&.  Upper and lower
case are equivalent\&. For example, -\fBBMP\fR is the same as -\fBbmp\fR\&. British spellings are also accepted\&. For example, -\fBgreyscale\fR\&.
.SS "Basic Options"
.PP
The following basic options are supported:
.sp
.ne 2
.mk
\fB-\fBgrayscale\fR\fR
.in +24n
.rt
Create
a monochrome JPEG file from color input\&. You should use this switch when compressing
a grayscale BMP file, because \fBcjpeg\fR cannot detect whether
a BMP file uses only shades of gray\&. By specifying the -\fBgrayscale\fR
option, you create a smaller JPEG file that takes less time to process\&.
.sp
.sp 1
.in -24n
.sp
.ne 2
.mk
\fB-\fBoptimize\fR\fR
.in +24n
.rt
Optimize
the entropy encoding parameters\&. If you do not specify this option, default
encoding parameters are used\&. -\fBoptimize\fR usually makes the
JPEG file a little smaller, but \fBcjpeg\fR runs more slowly
and needs much more memory\&. Image quality and speed of decompression are unaffected
by the -\fBoptimize\fR option\&.
.sp
.sp 1
.in -24n
.sp
.ne 2
.mk
\fB-\fBprogressive\fR\fR
.in +24n
.rt
Create
a progressive JPEG file\&. For more information about the -\fBprogressive\fR option, see the Extended Description section\&.
.sp
.sp 1
.in -24n
.sp
.ne 2
.mk
\fB-\fBquality \fIN\fR\fR\fR
.in +24n
.rt
Scale the quantization tables to adjust image quality\&. \fIN\fR ranges from 0 (worst) to 100 (best)\&. The default value is
75\&. For more information about the -\fBquality\fR option, see the
Extended Description section\&.
.sp
.sp 1
.in -24n
.sp
.ne 2
.mk
\fB-\fBtarga\fR\fR
.in +24n
.rt
Specify that
the input file is in Targa format\&. Targa files that contain an "identification"
field are not automatically recognized by \fBcjpeg\fR\&. For such
files, you must specify -\fBtarga\fR to make \fBcjpeg\fR
treat the input as Targa format\&. For most Targa files, you do not need this
switch\&.
.sp
.sp 1
.in -24n
.SS "Intermediate Options"
.PP
The following intermediate options are supported:
.sp
.ne 2
.mk
\fB-\fBdct fast\fR\fR
.in +24n
.rt
Use the
fast integer DCT method\&. This method is less accurate than the integer DCT
method or the floating-point DCT method\&.
.sp
.sp 1
.in -24n
.sp
.ne 2
.mk
\fB-\fBdct float\fR\fR
.in +24n
.rt
Use the
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\&. The results of the floating-point method may vary
slightly across machines, while the integer methods should give the same results
everywhere\&.
.sp
.sp 1
.in -24n
.sp
.ne 2
.mk
\fB-\fBdct int\fR\fR
.in +24n
.rt
Use the
integer DCT method\&. This is the default method\&.
.sp
.sp 1
.in -24n
.sp
.ne 2
.mk
\fB-\fBmaxmemory \fIN\fR\fR\fR
.in +24n
.rt
Set the limit for the amount of memory to use in processing
large images\&. \fIN\fR is specified in thousands of bytes,
or in millions of bytes if "M" is specified with the number\&. For example, -\fBmax 4m\fR selects 4000000 bytes\&. If more space is needed, temporary
files are used\&.
.sp
.sp 1
.in -24n
.sp
.ne 2
.mk
\fB-\fBoutfile \fIname\fR\fR\fR
.in +24n
.rt
Send the output image to the named file, instead of to the
standard output\&.
.sp
.sp 1
.in -24n
.sp
.ne 2
.mk
\fB-\fBrestart \fIN\fR\fR\fR
.in +24n
.rt
Emit a JPEG restart marker every \fIN\fR
MCU rows, or every \fIN\fR MCU blocks if "B" is specified
with the number\&. The default value is -\fBrestart 0\fR, which means
no restart markers\&. For more information about the -\fBrestart\fR
option, see the Extended Description section\&.
.sp
.sp 1
.in -24n
.sp
.ne 2
.mk
\fB-\fBsmooth \fIN\fR\fR\fR
.in +24n
.rt
Smooth the input image to eliminate dithering noise\&. \fIN\fR ranges from 1 to 100, and indicates the strength of smoothing\&.
The default value is -\fBsmooth 0\fR, which means no smoothing\&.
For more information about the -\fBsmooth\fR option, see the Extended
Description section\&.
.sp
.sp 1
.in -24n
.sp
.ne 2
.mk
\fB-\fBverbose\fR\fR
.in +24n
.rt
Display
version information at startup, and enable debug printout\&. The -\fBvv\fR option displays more verbose output than the -\fBv\fR
option\&. The -\fBvvv\fR option displays the most verbose output\&.
.sp
You can also use -\fBdebug\fR to specify this option\&.
.sp
.sp 1
.in -24n
.SS "Advanced Options"
.PP
The following advanced options are supported for advanced users only:
.sp
.ne 2
.mk
\fB-\fBbaseline\fR\fR
.in +24n
.rt
Force
baseline-compatible quantization tables to be generated\&. This clamps the quantization
values to 8 bits, even at low quality settings\&. This option is poorly named,
because -\fBbaseline\fR does not ensure that the output is actually
baseline JPEG\&. For example,  you can use the -\fBbaseline\fR and -\fBprogressive\fR options together\&.
.sp
.sp 1
.in -24n
.sp
.ne 2
.mk
\fB-\fBqslots \fIN\fR[,\&.\&.\&.]\fR\fR
.in +24n
.rt
Select which quantization table to use for each color component\&.
.sp
.sp 1
.in -24n
.sp
.ne 2
.mk
\fB-\fBqtables \fIfile\fR\fR\fR
.in +24n
.rt
Use the quantization tables provided in the specified text
file\&.
.sp
.sp 1
.in -24n
.sp
.ne 2
.mk
\fB-\fBsample HxV[,\&.\&.\&.]\fR\fR
.in +24n
.rt
Set the JPEG sampling factors for each color component\&.
.sp
.sp 1
.in -24n
.sp
.ne 2
.mk
\fB-\fBscans \fIfile\fR\fR\fR
.in +24n
.rt
Use the scan script provided in the specified text file\&.
.sp
.sp 1
.in -24n
.SH "OPERANDS"
.PP
The following operands are supported:
.sp
.ne 2
.mk
\fB\fB\fIfilename\fR\fR\fR
.in +24n
.rt
The name of the image file to be compressed\&.
.sp
.sp 1
.in -24n
.SH "EXTENDED DESCRIPTION"
.SS "The -\fBquality\fR Option"
.PP
The -\fBquality\fR option enables you to trade compressed
file size against the quality of the reconstructed image: the higher the quality
setting, the larger the JPEG file, and the greater the similarity between
the output image and the original input\&. Normally, you use the lowest quality
setting that decompresses into an output image that is visually indistinguishable
from the original image\&. For this purpose, the quality setting should be between
50 and 95\&. The default value of 75 is often just right\&. If you see defects
at -\fBquality 75\fR, increase the quality by 5 until you are happy
with the output image\&. The optimal setting varies from one image to another\&.
.PP
A value of -\fBquality 100\fR generates a quantization table
of ones\&. This minimizes loss in the quantization step, but information is
still lost in subsampling, as well as roundoff error\&. The -\fBquality
100\fR setting is mainly of interest for experimental purposes\&. Quality
values above 95 are not recommended for normal use, as the compressed file
size increases dramatically for very little gain in output image quality\&.
.PP
Quality values below 50 produce very small files of low image quality\&.
Settings of 5 to 10 might be useful in preparing an index of a large image
library, for example\&. Quality values below 25 generate 2-byte quantization
tables, which are considered optional in the JPEG standard\&. \fBcjpeg\fR
emits a warning message when you specify such a quality value, because some
other JPEG programs might be unable to decode the resulting file\&. Use -\fBbaseline\fR if you need to ensure compatibility at low quality values\&.
.SS "The -\fBprogressive\fR Option"
.PP
The -\fBprogressive\fR option 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 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, or a little smaller\&. Caution: progressive JPEG
is not yet widely implemented, so many decoders are unable to view a progressive
JPEG file at all\&.
.SS "The -\fBrestart\fR Option"
.PP
The -\fBrestart\fR option inserts extra markers that allow
a JPEG decoder to resynchronize after a transmission error\&. Without restart
markers, any damage to a compressed file usually ruins 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 from the point of the error
to the next restart marker\&. The restart markers occupy extra space\&. We recommend -\fBrestart 1\fR for images that are transmitted across unreliable networks\&.
.SS "The -\fBsmooth\fR Option"
.PP
The -\fBsmooth\fR option filters the input to eliminate fine-scale
noise\&. This option is often useful when you convert dithered images to JPEG:
a moderate smoothing factor of 10 to 50 deletes dithering patterns from the
input file, resulting in a smaller JPEG file and a better-looking image\&. If
the smoothing factor is too large, the image visibly blurs\&.
.SS "Hints"
.PP
Color GIF files are not the ideal input for JPEG\&. JPEG is really intended
for the compression of full-color 24-bit images\&. In particular, do not try
to convert cartoons, line drawings, or other images that have only a few distinct
colors\&. GIF works well on these, but JPEG does not\&. If you want to convert
a GIF file to JPEG, you should experiment with the -\fBquality\fR
and -\fBsmooth\fR options to get a satisfactory conversion\&. A value
of -\fBsmooth 10\fR is often helpful\&.
.PP
Avoid running an image through a series of JPEG compression/decompression
cycles\&. Image quality loss will accumulate\&. After ten cycles, the image may
be noticeably worse than it was after one cycle\&. Use a lossless format while
manipulating an image, then convert to JPEG format when you are ready to file
the image away\&. 
.PP
Use the -\fBoptimize\fR option when you make a "final" version
for posting or archiving\&. Also, when you use low quality settings, make very
small JPEG files\&. The percentage improvement is often much greater than on
larger files\&. At present, the -\fBoptimize\fR option is always selected
when generating progressive JPEG files\&.
.SH "EXAMPLES"
.PP
\fBExample 1: Compressing the PPM File test\&.ppm With a Quality Factor of 60 and Saving
the Output as test\&.jpg\fR
.PP
.PP
.nf
example% \fBcjpeg -quality 60 test\&.ppm > test\&.jpg\fR
.fi
.SH "ENVIRONMENT VARIABLES"
.PP
\fBcjpeg\fR uses the following environment variables:
.sp
.ne 2
.mk
\fBJPEGMEM\fR
.in +24n
.rt
The value of this environment
variable, if set, is the default memory limit\&. The value is specified as described
for the -\fBmaxmemory\fR option\&. JPEGMEM overrides the default value
specified when the program was compiled, and is in turn overridden by an explicit -\fBmaxmemory\fR option\&.
.sp
.sp 1
.in -24n
.SH "ATTRIBUTES"
.PP
See \fBattributes\fR(5)
for descriptions of the following attributes:
.sp
.TS
tab() allbox;
cw(2.750000i)| cw(2.750000i)
lw(2.750000i)| lw(2.750000i).
ATTRIBUTE TYPEATTRIBUTE VALUE
Availabilityimage/library/libjpeg
Interface stabilityUncommitted
.TE
.sp
.SH "SEE ALSO"
.PP
Wallace, Gregory K\&., \fIThe JPEG Still Picture Compression Standard\fR Communications of the ACM, April 1991 (vol\&. 34, no\&. 4), pp\&. 30-44\&.
.PP
\fBdjpeg\fR(1), \fBjpegtran\fR(1), \fBrdjpgcom\fR(1), \fBwrjpgcom\fR(1)
.SH "NOTES"
.PP
Arithmetic coding is not supported\&. GIF input files are not supported\&.
Not all variants of BMP and Targa file formats are supported\&.
.PP
This man page was originally written by the Independent JPEG Group\&.
Updated by Breda McColgan, Sun Microsystems Inc\&., 2004\&. 
...\" created by instant / solbook-to-man, Thu 20 Mar 2014, 02:30
...\" LSARC 2003/085 libtiff, libjpeg, and libpng