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DJPEG(1) USER COMMANDS DJPEG(1)
NAME
djpeg - decompress a JPEG file to an image file
SYNOPSIS
djpeg [ -GPRTgD1bd ] [ -q _✓c_✓o_✓l_✓o_✓r_✓s ] [ -m _✓m_✓e_✓m_✓o_✓r_✓y ] [ _✓f_✓i_✓l_✓e_✓n_✓a_✓m_✓e
]
DESCRIPTION
djpeg decompresses the named JPEG file, or the standard
input if no file is named, and produces an image file on the
standard output. PPM, GIF, Targa, or RLE output format can
be selected. (RLE is supported only if the URT library is
available.)
OPTIONS
-G Select GIF output format (implies -q, with default of
256 colors).
-P Select PPM or PGM output format (this is the default).
PGM is emitted if the JPEG file is gray-scale or if -g
is specified.
-R Select RLE output format. Requires URT library.
-T Select Targa output format. Gray-scale format is emit-
ted if the JPEG file is gray-scale or if -g is speci-
fied; otherwise, colormapped format is emitted if -q is
specified; otherwise, 24-bit full-color format is emit-
ted.
-g Force gray-scale output even if input is color.
-q _✓N Quantize to N colors. This reduces the number of
colors in the output image so that it can be displayed
on a colormapped display or stored in a colormapped
file format. For example, if you have an 8-bit
display, you'd need to quantize to 256 or fewer colors.
-D Do not use dithering in color quantization. By
default, Floyd-Steinberg dithering is applied when
quantizing colors, but on some images dithering may
result in objectionable "graininess". If that happens,
you can turn off dithering with -D. -D is ignored
unless you also say -q or -G.
-1 Use one-pass instead of two-pass color quantization.
The one-pass method is faster and needs less memory,
but it produces a lower-quality image. -1 is ignored
unless you also say -q or -G. Also, the one-pass
method is always used for gray-scale output (the two-
pass method is no improvement then).
Sun Release 4.1 Last change: 28 February 1992 1
DJPEG(1) USER COMMANDS DJPEG(1)
-b Perform cross-block smoothing. This is quite memory-
intensive and only seems to improve the image at low
quality settings (-Q 10 to 20 or so). At normal -Q
settings it may make the image worse.
-d Enable debug printout. More -d's give more output.
Also, version information is printed at startup.
-m _✓m_✓e_✓m_✓o_✓r_✓y
Set limit for amount of memory to use in processing
large images. Value is in thousands of bytes, or mil-
lions of bytes if "M" is attached to the number. For
example, -m 4m selects 4000000 bytes. If more space is
needed, temporary files will be used.
EXAMPLES
This example decompresses the JPEG file foo.jpg, quantizes
to 256 colors, and saves the output in GIF format in
foo.gif:
djpeg -G _✓f_✓o_✓o._✓j_✓p_✓g > _✓f_✓o_✓o._✓g_✓i_✓f
SEE ALSO
cjpeg(1)
ppm(5), pgm(5)
Wallace, Gregory K. "The JPEG Still Picture Compression
Standard", Communications of the ACM, April 1991 (vol. 34,
no. 4), pp. 30-44.
AUTHOR
Independent JPEG Group
BUGS
Arithmetic coding is not supported for legal reasons.
Not as fast as we'd like.
Sun Release 4.1 Last change: 28 February 1992 2