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ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4. The directory name has changed: no version number in the expanded directory now.
author Franz Glasner <fzglas.hg@dom66.de>
date Mon, 15 Sep 2025 11:43:07 +0200
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1 .TH DJPEG 1 "28 April 2019"
2 .SH NAME
3 djpeg \- decompress a JPEG file to an image file
4 .SH SYNOPSIS
5 .B djpeg
6 [
7 .I options
8 ]
9 [
10 .I filename
11 ]
12 .LP
13 .SH DESCRIPTION
14 .LP
15 .B djpeg
16 decompresses the named JPEG file, or the standard input if no file is named,
17 and produces an image file on the standard output. PBMPLUS (PPM/PGM), BMP,
18 GIF, Targa, or RLE (Utah Raster Toolkit) output format can be selected.
19 (RLE is supported only if the URT library is available, which it isn't
20 on most non-Unix systems.)
21 .SH OPTIONS
22 All switch names may be abbreviated; for example,
23 .B \-grayscale
24 may be written
25 .B \-gray
26 or
27 .BR \-gr .
28 Most of the "basic" switches can be abbreviated to as little as one letter.
29 Upper and lower case are equivalent (thus
30 .B \-BMP
31 is the same as
32 .BR \-bmp ).
33 British spellings are also accepted (e.g.,
34 .BR \-greyscale ),
35 though for brevity these are not mentioned below.
36 .PP
37 The basic switches are:
38 .TP
39 .BI \-colors " N"
40 Reduce image to at most N colors. This reduces the number of colors used in
41 the output image, so that it can be displayed on a colormapped display or
42 stored in a colormapped file format. For example, if you have an 8-bit
43 display, you'd need to reduce to 256 or fewer colors.
44 .TP
45 .BI \-quantize " N"
46 Same as
47 .BR \-colors .
48 .B \-colors
49 is the recommended name,
50 .B \-quantize
51 is provided only for backwards compatibility.
52 .TP
53 .B \-fast
54 Select recommended processing options for fast, low quality output. (The
55 default options are chosen for highest quality output.) Currently, this is
56 equivalent to \fB\-dct fast \-nosmooth \-onepass \-dither ordered\fR.
57 .TP
58 .B \-grayscale
59 Force grayscale output even if JPEG file is color.
60 Useful for viewing on monochrome displays; also,
61 .B djpeg
62 runs noticeably faster in this mode.
63 .TP
64 .B \-rgb
65 Force RGB output even if JPEG file is grayscale.
66 This is provided to support applications that don't
67 want to cope with grayscale as a separate case.
68 .TP
69 .BI \-scale " M/N"
70 Scale the output image by a factor M/N. Currently supported scale factors are
71 M/N with all M from 1 to 16, where N is the source DCT size, which is 8 for
72 baseline JPEG. If the /N part is omitted, then M specifies the DCT scaled
73 size to be applied on the given input. For baseline JPEG this is equivalent
74 to M/8 scaling, since the source DCT size for baseline JPEG is 8.
75 Scaling is handy if the image is larger than your screen; also,
76 .B djpeg
77 runs much faster when scaling down the output.
78 .TP
79 .B \-bmp
80 Select BMP output format (Windows flavor).
81 8-bit colormapped format is emitted if
82 .B \-colors
83 or
84 .B \-grayscale
85 is specified, or if the JPEG file is grayscale; otherwise, 24-bit full-color
86 format is emitted.
87 .TP
88 .B \-gif
89 Select GIF output format (LZW compressed).
90 Since GIF does not support more than 256 colors,
91 .B \-colors 256
92 is assumed (unless you specify a smaller number of colors). If you specify
93 .BR \-fast ,
94 the default number of colors is 216.
95 .TP
96 .B \-gif0
97 Select GIF output format (uncompressed).
98 Since GIF does not support more than 256 colors,
99 .B \-colors 256
100 is assumed (unless you specify a smaller number of colors). If you specify
101 .BR \-fast ,
102 the default number of colors is 216.
103 .TP
104 .B \-os2
105 Select BMP output format (OS/2 1.x flavor).
106 8-bit colormapped format is emitted if
107 .B \-colors
108 or
109 .B \-grayscale
110 is specified, or if the JPEG file is grayscale; otherwise, 24-bit full-color
111 format is emitted.
112 .TP
113 .B \-pnm
114 Select PBMPLUS (PPM/PGM) output format (this is the default format).
115 PGM is emitted if the JPEG file is grayscale or if
116 .B \-grayscale
117 is specified; otherwise PPM is emitted.
118 .TP
119 .B \-rle
120 Select RLE output format. (Requires URT library.)
121 .TP
122 .B \-targa
123 Select Targa output format. Grayscale format is emitted if the JPEG file is
124 grayscale or if
125 .B \-grayscale
126 is specified; otherwise, colormapped format is emitted if
127 .B \-colors
128 is specified; otherwise, 24-bit full-color format is emitted.
129 .PP
130 Switches for advanced users:
131 .TP
132 .B \-dct int
133 Use integer DCT method (default).
134 .TP
135 .B \-dct fast
136 Use fast integer DCT (less accurate).
137 .TP
138 .B \-dct float
139 Use floating-point DCT method.
140 The float method is very slightly more accurate than the int method, but is
141 much slower unless your machine has very fast floating-point hardware. Also
142 note that results of the floating-point method may vary slightly across
143 machines, while the integer methods should give the same results everywhere.
144 The fast integer method is much less accurate than the other two.
145 .TP
146 .B \-dither fs
147 Use Floyd-Steinberg dithering in color quantization.
148 .TP
149 .B \-dither ordered
150 Use ordered dithering in color quantization.
151 .TP
152 .B \-dither none
153 Do not use dithering in color quantization.
154 By default, Floyd-Steinberg dithering is applied when quantizing colors; this
155 is slow but usually produces the best results. Ordered dither is a compromise
156 between speed and quality; no dithering is fast but usually looks awful. Note
157 that these switches have no effect unless color quantization is being done.
158 Ordered dither is only available in
159 .B \-onepass
160 mode.
161 .TP
162 .BI \-map " file"
163 Quantize to the colors used in the specified image file. This is useful for
164 producing multiple files with identical color maps, or for forcing a
165 predefined set of colors to be used. The
166 .I file
167 must be a GIF or PPM file. This option overrides
168 .B \-colors
169 and
170 .BR \-onepass .
171 .TP
172 .B \-nosmooth
173 Don't use high-quality upsampling.
174 .TP
175 .B \-onepass
176 Use one-pass instead of two-pass color quantization. The one-pass method is
177 faster and needs less memory, but it produces a lower-quality image.
178 .B \-onepass
179 is ignored unless you also say
180 .B \-colors
181 .IR N .
182 Also, the one-pass method is always used for grayscale output (the two-pass
183 method is no improvement then).
184 .TP
185 .BI \-maxmemory " N"
186 Set limit for amount of memory to use in processing large images. Value is
187 in thousands of bytes, or millions of bytes if "M" is attached to the
188 number. For example,
189 .B \-max 4m
190 selects 4000000 bytes. If more space is needed, temporary files will be used.
191 .TP
192 .BI \-outfile " name"
193 Send output image to the named file, not to standard output.
194 .TP
195 .B \-verbose
196 Enable debug printout. More
197 .BR \-v 's
198 give more output. Also, version information is printed at startup.
199 .TP
200 .B \-debug
201 Same as
202 .BR \-verbose .
203 .SH EXAMPLES
204 .LP
205 This example decompresses the JPEG file foo.jpg, quantizes it to
206 256 colors, and saves the output in 8-bit BMP format in foo.bmp:
207 .IP
208 .B djpeg \-colors 256 \-bmp
209 .I foo.jpg
210 .B >
211 .I foo.bmp
212 .SH HINTS
213 To get a quick preview of an image, use the
214 .B \-grayscale
215 and/or
216 .B \-scale
217 switches.
218 .B \-grayscale \-scale 1/8
219 is the fastest case.
220 .PP
221 Several options are available that trade off image quality to gain speed.
222 .B \-fast
223 turns on the recommended settings.
224 .PP
225 .B \-dct fast
226 and/or
227 .B \-nosmooth
228 gain speed at a small sacrifice in quality.
229 When producing a color-quantized image,
230 .B \-onepass \-dither ordered
231 is fast but much lower quality than the default behavior.
232 .B \-dither none
233 may give acceptable results in two-pass mode, but is seldom tolerable in
234 one-pass mode.
235 .PP
236 If you are fortunate enough to have very fast floating point hardware,
237 \fB\-dct float\fR may be even faster than \fB\-dct fast\fR. But on most
238 machines \fB\-dct float\fR is slower than \fB\-dct int\fR; in this case it is
239 not worth using, because its theoretical accuracy advantage is too small to be
240 significant in practice.
241 .SH ENVIRONMENT
242 .TP
243 .B JPEGMEM
244 If this environment variable is set, its value is the default memory limit.
245 The value is specified as described for the
246 .B \-maxmemory
247 switch.
248 .B JPEGMEM
249 overrides the default value specified when the program was compiled, and
250 itself is overridden by an explicit
251 .BR \-maxmemory .
252 .SH SEE ALSO
253 .BR cjpeg (1),
254 .BR jpegtran (1),
255 .BR rdjpgcom (1),
256 .BR wrjpgcom (1)
257 .br
258 .BR ppm (5),
259 .BR pgm (5)
260 .br
261 Wallace, Gregory K. "The JPEG Still Picture Compression Standard",
262 Communications of the ACM, April 1991 (vol. 34, no. 4), pp. 30-44.
263 .SH AUTHOR
264 Independent JPEG Group