DJPEG

NAME

SYNOPSIS

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. PBMPLUS (PPM/PGM), GIF, Targa, or RLE (Utah Raster Toolkit) output format can be selected. (RLE is supported only if the URT library is available.)  

OPTIONS

The basic switches are:

-colors N

Reduce image to at most N colors. This reduces the number of colors used 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 reduce to 256 or fewer colors.

-quantize N

Same as -colors. -colors is the recommended name, -quantize is provided only for backwards compatibility.

-gif

Select GIF output format. Since GIF does not support more than 256 colors, -colors 256 is assumed (unless you specify a smaller number of colors).

-pnm

Select PBMPLUS (PPM/PGM) output format (this is the default format). PGM is emitted if the JPEG file is gray-scale or if -grayscale is specified; otherwise PPM is emitted.

-rle

Select RLE output format. (Requires URT library.)

-targa

Select Targa output format. Gray-scale format is emitted if the JPEG file is gray-scale or if -grayscale is specified; otherwise, colormapped format is emitted if -colors is specified; otherwise, 24-bit full-color format is emitted.

Switches for advanced users:

-blocksmooth

Perform cross-block smoothing. This is quite memory-intensive and only seems to improve the image at very low quality settings (-quality 10 to 20 or so). At normal quality settings it may make the image worse.

-grayscale

Force gray-scale output even if JPEG file is color. Useful for viewing on monochrome displays.

-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, -max 4m selects 4000000 bytes. If more space is needed, temporary files will be used.

-nodither

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 -nodither. -nodither is ignored unless you also say -colors N.

-onepass

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. -onepass is ignored unless you also say -colors N. Also, the one-pass method is always used for gray-scale output (the two-pass method is no improvement then).

-verbose

Enable debug printout. More -v's give more output. Also, version information is printed at startup.

-debug

Same as -verbose.

EXAMPLES

This example decompresses the JPEG file foo.jpg, automatically quantizes to 256 colors, and saves the output in GIF format in foo.gif:

djpeg -gif foo.jpg > foo.gif

ENVIRONMENT

JPEGMEM

If this environment variable is set, its value is the default memory limit. The value is specified as described for the -maxmemory switch. JPEGMEM overrides the default value specified when the program was compiled, and itself is overridden by an explicit -maxmemory.

SEE ALSO

AUTHOR

BUGS

Still not as fast as we'd like.

Index

NAME

SYNOPSIS

DESCRIPTION

OPTIONS

EXAMPLES

ENVIRONMENT

SEE ALSO

AUTHOR

BUGS