'\" te
.TH djpeg 1 "26 Mar 2004" "SunOS 5.11" "User Commands"
.SH "NAME"
djpeg \- decompress
a JPEG file to an image file
.SH "SYNOPSIS"
.PP
\fBdjpeg\fR [\fB\fIoptions\fR\fR] [\fB\fIfilename\fR\fR]
.SH "DESCRIPTION"
.PP
\fBdjpeg\fR decompresses the named JPEG file, or the standard
input if no file is named, and produces an image file on the standard output\&.
The following output file formats are currently supported:
.sp
.in +2
\(bu
.mk
.in +3
.rt
BMP
.sp
.in -3
\(bu
.mk
.in +3
.rt
GIF
.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-\fBbmp\fR\fR
.in +16n
.rt
Specify that
the output file is in BMP format, Windows flavor\&. 8-bit colormapped format
is displayed if -\fBcolors\fR or -\fBgrayscale\fR is specified,
or if the JPEG file is grayscale\&. Otherwise, 24-bit full-color format is displayed\&.
.sp
.sp 1
.in -16n
.sp
.ne 2
.mk
\fB-\fBcolors \fIN\fR\fR\fR
.in +16n
.rt
Reduce the image to at most \fIN\fR colors\&.
This option reduces the number of colors used in the output image, so that
the output image can be displayed on a colormapped display or stored in a
colormapped file format\&. For example, if you have an 8-bit display, you must
reduce to 256 colors or less\&. 
.sp
You can also use -\fBquantize\fR to specify this option\&. However, -\fBcolors\fR is the recommended option name\&. The -\fBquantize\fR
option is provided only for backwards compatibility\&.
.sp
.sp 1
.in -16n
.sp
.ne 2
.mk
\fB-\fBfast\fR\fR
.in +16n
.rt
Select the
recommended processing options for fast, low-quality output\&. The default options
are chosen for highest quality output\&. Currently, this is equivalent to -\fBdct fast\fR -\fBnosmooth\fR -\fBonepass\fR -\fBdither ordered\fR\&.
.sp
.sp 1
.in -16n
.sp
.ne 2
.mk
\fB-\fBgif\fR\fR
.in +16n
.rt
Specify that
the output file is in GIF format\&. GIF does not support more than 256 colors,
so -\fBcolors 256\fR is assumed unless you specify a smaller number
of colors\&.
.sp
.sp 1
.in -16n
.sp
.ne 2
.mk
\fB-\fBgrayscale\fR\fR
.in +16n
.rt
Create
a monochrome image file even if the JPEG file is a color file\&. This option
is useful for viewing images on monochrome displays\&. \fBdjpeg\fR
runs noticeably faster in this mode\&.
.sp
.sp 1
.in -16n
.sp
.ne 2
.mk
\fB-\fBos2\fR\fR
.in +16n
.rt
Specify that
the output file is in BMP format, OS/2 1\&.x flavor\&. 8-bit colormapped format
is displayed if -\fBcolors\fR or -\fBgrayscale\fR is specified,
or if the JPEG file is grayscale\&. Otherwise, 24-bit full-color format is displayed\&.
.sp
.sp 1
.in -16n
.sp
.ne 2
.mk
\fB-\fBpnm\fR\fR
.in +16n
.rt
Specify that
the output file is in PBMPLUS format\&. PGM format is displayed if -\fBgrayscale\fR is specified, or if the JPEG file is grayscale\&. Otherwise,
PPM format is displayed\&.
.sp
.sp 1
.in -16n
.sp
.ne 2
.mk
\fB-\fBrle\fR\fR
.in +16n
.rt
Specify that
the output file is in RLE format\&. This option requires the URT library\&.
.sp
.sp 1
.in -16n
.sp
.ne 2
.mk
\fB-\fBscale \fIM\fR/\fIN\fR\fR\fR
.in +16n
.rt
Scale the output image by a
factor \fIM\fR/\fIN\fR\&. Currently,
the scale factor must be 1/1, 1/2, 1/4, or 1/8\&. Scaling is useful if the image
is larger than  your screen\&. \fBdjpeg\fR runs much faster when
scaling down the output\&.
.sp
.sp 1
.in -16n
.sp
.ne 2
.mk
\fB-\fBtarga\fR\fR
.in +16n
.rt
Specify that
the output file is in Targa format\&. Grayscale format is displayed if -\fBgrayscale\fR is specified, or if the JPEG file is grayscale\&. Colormapped
format is displayed if -\fBcolors\fR is specified\&. Otherwise, 24-bit
full-color format is displayed\&.
.sp
.sp 1
.in -16n
.SS "Intermediate Options"
.PP
The following intermediate options are supported:
.sp
.ne 2
.mk
\fB-\fBdct fast\fR\fR
.in +16n
.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 -16n
.sp
.ne 2
.mk
\fB-\fBdct float\fR\fR
.in +16n
.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 -16n
.sp
.ne 2
.mk
\fB-\fBdct int\fR\fR
.in +16n
.rt
Use the
integer DCT method\&. This is the default method\&.
.sp
.sp 1
.in -16n
.sp
.ne 2
.mk
\fB-\fBdither fs\fR\fR
.in +16n
.rt
Use Floyd-Steinberg
dithering in color quantization\&. By default, Floyd-Steinberg dithering is
applied when quantizing colors\&. This process is slow but usually produces
the best results\&. This option has no effect unless color quantization is being
done\&.
.sp
.sp 1
.in -16n
.sp
.ne 2
.mk
\fB-\fBdither none\fR\fR
.in +16n
.rt
Do
not use dithering in color quantization\&. No dithering is fast but is usually
of poor quality\&. This option has no effect unless color quantization is being
done\&.
.sp
.sp 1
.in -16n
.sp
.ne 2
.mk
\fB-\fBdither ordered\fR\fR
.in +16n
.rt
Use ordered dithering in color quantization\&. Ordered dither is a compromise
between speed and quality\&. Ordered dither is only available in -\fBonepass\fR mode\&. This option has no effect unless color quantization is being
done\&.
.sp
.sp 1
.in -16n
.sp
.ne 2
.mk
\fB-\fBmap \fIfile\fR\fR\fR
.in +16n
.rt
Quantize to the colors used in the specified image file\&. This
option is useful for producing multiple files with identical color maps, or
for forcing a predefined set of colors to be used\&. \fIfile\fR
must be a GIF or PPM file\&. This option overrides the -\fBcolors\fR
and -\fBonepass\fR options\&.
.sp
.sp 1
.in -16n
.sp
.ne 2
.mk
\fB-\fBmaxmemory \fIN\fR\fR\fR
.in +16n
.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 -16n
.sp
.ne 2
.mk
\fB-\fBnosmooth\fR\fR
.in +16n
.rt
Use a
faster, lower-quality upsampling routine\&.
.sp
.sp 1
.in -16n
.sp
.ne 2
.mk
\fB-\fBonepass\fR\fR
.in +16n
.rt
Use one-pass
instead of two-pass color quantization\&. The one-pass method is faster and
requires less memory, but produces a lower-quality image\&. The -\fBonepass\fR option is ignored unless you also specify the -\fBcolors \fIN\fR\fR option\&. The one-pass method is always used for grayscale
output, the two-pass method provides no improvement for such output\&.
.sp
.sp 1
.in -16n
.sp
.ne 2
.mk
\fB-\fBoutfile \fIname\fR\fR\fR
.in +16n
.rt
Send the output image to the named file, instead of to the
standard output\&.
.sp
.sp 1
.in -16n
.sp
.ne 2
.mk
\fB-\fBverbose\fR\fR
.in +16n
.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\&.
You can also use -\fBdebug\fR to specify the verbose option\&.
.sp
.sp 1
.in -16n
.SH "OPERANDS"
.PP
The following operands are supported:
.sp
.ne 2
.mk
\fB\fB\fIfilename\fR\fR\fR
.in +16n
.rt
The name of the JPEG file to be decompressed\&.
.sp
.sp 1
.in -16n
.SH "EXTENDED DESCRIPTION"
.SS "Hints"
.PP
To get a quick preview of an image, use the -\fBgrayscale\fR
or -\fBscale\fR options, or a combination of both options\&. For example, -\fBgrayscale\fR -\fBscale 1/8\fR is the fastest case\&.
.PP
Several options trade image quality to gain speed\&. The -\fBfast\fR option configures the recommended settings\&.
.PP
The -\fBdct fast\fR and -\fBnosmooth\fR options
gain speed for a small sacrifice in quality\&. When producing a color-quantized
image, -\fBonepass\fR -\fBdither ordered\fR is fast but
much lower quality than the default behavior\&. -\fBdither none\fR
may give acceptable results in two-pass mode, but is seldom tolerable in one-pass
mode\&. 
.PP
If you have very fast floating point hardware, -\fBdct float\fR
may be even faster than -\fBdct fast\fR\&. However, on most machines, -\fBdct float\fR is slower than -\fBdct int\fR\&. In such cases,
do not use -\fBdct float\fR, because the theoretical accuracy advantage
is too small to be significant in practice\&.
.SH "EXAMPLES"
.PP
\fBExample 1: Decompressing the JPEG File test\&.jpg, Quantizing to 256 Colors, and
Saving the Output in 8-bit BMP Format as test\&.bmp\fR
.PP
.PP
.nf
example% \fBdjpeg -colors 256 -bmp test\&.jpg > test\&.bmp\fR
.fi
.SH "ENVIRONMENT VARIABLES"
.PP
\fBdjpeg\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
\fBcjpeg\fR(1), \fBjpegtran\fR(1), \fBrdjpgcom\fR(1), \fBwrjpgcom\fR(1)
.SH "NOTES"
.PP
Arithmetic coding is not supported\&. \fBdjpeg\fR produces
uncompressed GIF files\&. These large files are readable by standard GIF decoders\&.
.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