The Independent JPEG Group's JPEG software v3
diff --git a/djpeg.1 b/djpeg.1
index 5eec670..df4064c 100644
--- a/djpeg.1
+++ b/djpeg.1
@@ -1,13 +1,16 @@
-.TH DJPEG 1 "11 December 1991"
+.TH DJPEG 1 "28 February 1992"
.SH NAME
djpeg \- decompress a JPEG file to an image file
.SH SYNOPSIS
.B djpeg
[
-.B \-GPRTbgD2d
+.B \-GPRTgD1bd
]
[
-.BI \-q " N"
+.BI \-q " colors"
+]
+[
+.BI \-m " memory"
]
[
.I filename
@@ -20,22 +23,12 @@
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.)
-.LP
-The color quantization algorithm is currently shoddy. Because of this, the
-GIF output mode is not recommended in the current release, except for
-gray-scale output (obtained with
-.BR \-g ).
.SH OPTIONS
.TP
.B \-G
Select GIF output format (implies
.BR \-q ,
with default of 256 colors).
-Currently the color quantization uses a shoddy algorithm and external
-quantization (e.g.
-.IR ppmquant ,
-.IR rlequant )
-is recommended before conversion to GIF format.
.TP
.B \-P
Select PPM or PGM output format (this is the default). PGM is emitted if the
@@ -54,18 +47,14 @@
.B \-q
is specified; otherwise, 24-bit full-color format is emitted.
.TP
-.B \-b
-Perform cross-block smoothing. This is quite memory-intensive and only seems
-to improve the image at low quality settings (\fB\-Q\fR 10 to 20 or so).
-At normal
-.B \-Q
-settings it may make the image worse.
-.TP
.B \-g
Force gray-scale output even if input is color.
.TP
.BI \-q " N"
-Quantize to N colors.
+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.
.TP
.B \-D
Do not use dithering in color quantization. By default, Floyd-Steinberg
@@ -73,42 +62,61 @@
result in objectionable "graininess". If that happens, you can turn off
dithering with
.BR \-D .
+.B \-D
+is ignored unless you also say
+.B \-q
+or
+.BR \-G .
.TP
-.B \-2
-Use two-pass color quantization (not yet supported).
+.B \-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.
+.B \-1
+is ignored unless you also say
+.B \-q
+or
+.BR \-G .
+Also, the one-pass method is always used for gray-scale output (the two-pass
+method is no improvement then).
+.TP
+.B \-b
+Perform cross-block smoothing. This is quite memory-intensive and only seems
+to improve the image at low quality settings (\fB\-Q\fR 10 to 20 or so).
+At normal
+.B \-Q
+settings it may make the image worse.
.TP
.B \-d
Enable debug printout. More
.BR \-d 's
give more output. Also, version information is printed at startup.
+.TP
+.BI \-m " memory"
+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 \-m 4m
+selects 4000000 bytes. If more space is needed, temporary files will be used.
.SH EXAMPLES
.LP
-This example decompresses the JPEG file foo.jpg and saves the output
-as a gray-scale image in foo.pgm:
+This example decompresses the JPEG file foo.jpg, quantizes to 256 colors,
+and saves the output in GIF format in foo.gif:
.IP
-.B djpeg \-g
+.B djpeg \-G
.I foo.jpg
.B >
-.I foo.pgm
+.I foo.gif
.SH SEE ALSO
.BR cjpeg (1)
.br
-.BR ppmquant (1)
-[From the PBMplus distribution]
-.br
-.BR rlequant (1)
-[From the Utah Raster Toolkit distribution]
+.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
-.B djpeg
-currently uses a shoddy color quantization algorithm. This leads to
-poor GIF file output. Two-pass color quantization is not yet
-supported.
-.PP
Arithmetic coding is not supported for legal reasons.
.PP
Not as fast as we'd like.