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1 perry 1 JPEGTOPNM
2 !!!JPEGTOPNM
3 NAME
4 SYNOPSIS
5 DESCRIPTION
6 OPTIONS
7 EXAMPLES
8 HINTS
9 ENVIRONMENT
10 SEE ALSO
11 LIMITATIONS
12 AUTHOR
13 ----
14 !!NAME
15
16
17 jpegtopnm - convert JPEG/JFIF file to portable pixmap or graymap
18 !!SYNOPSIS
19
20
21 __jpegtopnm__ [[__-dct__
22 {__int__|__fast__|__float__}] [[__-nosmooth__]
23 [[__-maxmemory__ ''N'']
24 [[{__-adobe__|__-notadobe__}] [[__-comments__]
25 [[__-dumpexif__] [[__-exif=__''filespec'']
26 [[__-verbose__] [[__-tracelevel__ ''N''] [[
27 ''filename'' ]
28
29
30 All options may be abbreviated to their shortest unique
31 prefix.
32 !!DESCRIPTION
33
34
35 __jpegtopnm__ converts the named JFIF file, or the
36 standard input if no file is named to a PPM or PGM image
37 file on the standard output. If the JFIF file is of the
38 grayscale variety, __jpegtopnm__ generates a PGM
39 (Portable Graymap) file. Otherwise, it generates a PPM
40 (Portable Pixmap) file.
41
42
43 __jpegtopnm__ uses the Independent JPEG Group's JPEG
44 library to interpret the input file. See
45 __http://www.ijg.org__ for information on the
46 library.
47
48
49
50
51 EXIF is an image format that is a subformat of JFIF (to wit,
52 a JFIF file that contains an EXIF header as an APP1 marker).
53 __jpegtopnm__ handles EXIF.
54
55
56 JFIF files can have either 8 bits per sample or 12 bits per
57 sample. The 8 bit variety is by far the most common. There
58 are two versions of the IJG JPEG library. One reads only 8
59 bit files and the other reads only 12 bit files. You must
60 link the appropriate one of these libraries with
61 __jpegtopnm__. Ordinarily, this means the library is in
62 your shared library search path when you run
63 __jpegtopnm__.
64
65
66 __jpegtopnm__ generates output with either one byte or
67 two bytes per sample depending on whether the JFIF input has
68 either 8 bits or 12 bits per sample. You can use
69 __pnmdepth__ to reduce a two-byte-per-sample file to a
70 one-byte-per-sample file if you need to.
71
72
73 If the JFIF file uses the CMYK or YCCK color space, the
74 input does not actually contain enough information to know
75 what color each pixel is. To know what color a pixel is, one
76 would have to know the properties of the inks to which the
77 color space refers. __jpegtopnm__ interprets the colors
78 using the common transformation which assumes all the inks
79 are simply subtractive and linear.
80 !!OPTIONS
81
82
83 The options are only for advanced users:
84
85
86 __-dct int__
87
88
89 Use integer DCT method (default).
90
91
92 __-dct fast__
93
94
95 Use fast integer DCT (less accurate).
96
97
98 __-dct float__
99
100
101 Use floating-point DCT method. The float method is very
102 slightly more accurate than the int method, but is much
103 slower unless your machine has very fast floating-point
104 hardware. Also note that results of the floating-point
105 method may vary slightly across machines, while the integer
106 methods should give the same results everywhere. The fast
107 integer method is much less accurate than the other
108 two.
109
110
111 __-nosmooth__
112
113
114 Use a faster, lower-quality upsampling routine.
115
116
117 __-maxmemory__ ''N''
118
119
120 Set limit on the amount of memory __jpegtopnm__ uses in
121 processing large images. Value is in thousands of bytes, or
122 millions of bytes if
123 __-maxmemory 4m__ selects 4000000
124 bytes. If __jpegtopnm__ needs more space, it uses
125 temporary files.
126
127
128 __-adobe__
129
130
131 __-notadobe__
132
133
134 There are two variations on the CMYK (and likewise YCCK)
135 color space that may be used in the JFIF input. In the
136 normal one, a zero value for a color components indicates
137 absence of ink. In the other, a zero value means the maximum
138 ink coverage. The latter is used by Adobe Photoshop when it
139 creates a bare JFIF output file (but not when it creates
140 JFIF output as part of Encapsulated Postscript
141 output).
142
143
144 These options tell __jpegtopnm__ which version of the
145 CMYK or YCCK color space the image uses. If you specify
146 neither, __jpegtopnm__ tries to figure it out on its own.
147 In the present version, it doesn't try very hard at all: It
148 just assumes the Photoshop version, since Photoshop and its
149 emulators seem to be the main source of CMYK and YCCK
150 images. But with experience of use, future versions might be
151 more sophisticated.
152
153
154 If the JFIF image does not indicate that it is CMYK or YCCK,
155 these options have no effect.
156
157
158 If you don't use the right one of these options, the symptom
159 is output that looks like a negative.
160
161
162 __-dumpexif__
163
164
165 Print the interpreted contents of any Exif header in the
166 input file to the Standard Error file. Similar to the
167 program __jhead__ (not part of the Netpbm
168 package).
169
170
171 __-exif=__''filespec''
172
173
174 Extract the contents of the EXIF header from the input image
175 and write it to the file ''filespec''. ''filespec'' =
176 __-__ means write it to Standard Output. In this case,
177 __jpegtopnm__ does not output the converted image at
178 all.
179
180
181 __jpegtopnm__ writes the contents of the EXIF header
182 byte-for-byte, starting with the two byte length field
183 (which length includes those two bytes).
184
185
186 You can use this file as input to __ppmtojpeg__ to insert
187 an identical EXIF header into a new JFIF image.
188
189
190 If there is no EXIF header, __jpegtopnm__ writes two
191 bytes of binary zero and nothing else.
192
193
194 An EXIF header takes the form of a JFIF APP1 marker. Only
195 the first such marker within the JFIF header
196 counts.
197
198
199 __-comments__
200
201
202 Print any comments in the input file to the Standard Error
203 file.
204
205
206 __-verbose__
207
208
209 Print details about the conversion to the Standard Error
210 file.
211
212
213 __-tracelevel__ ''n''
214
215
216 Turn on the JPEG library's trace messages to the Standard
217 Error file. A higher value of ''n'' gets more trace
218 information. __-verbose__ implies a trace level of at
219 least 1.
220 !!EXAMPLES
221
222
223 This example converts the color JFIF file foo.jpg to a PPM
224 file named foo.ppm:
225
226
227 __jpegtopnm foo.jpg __
228 !!HINTS
229
230
231 You can use __ppmquant__ to color quantize the result,
232 i.e. to reduce the number of distinct colors in the image.
233 In fact, you may have to if you want to convert the PPM file
234 to certain other formats. __ppmdither__ Does a more
235 sophisticated quantization.
236
237
238 Use __pnmscale__ to change the dimensions of the
239 resulting image.
240
241
242 Use __ppmtopgm__ to convert a color JFIF file to a
243 grayscale PGM file.
244
245
246 You can easily use these converters together.
247 E.g.:
248
249
250 __jpegtopnm foo.jpg | ppmtopgm | pnmscale .25
251
252
253 __-dct fast__ and/or __-nosmooth__ gain speed at a
254 small sacrifice in quality.
255
256
257 If you are fortunate enough to have very fast floating point
258 hardware, __-dct float__ may be even faster than __-dct
259 fast__. But on most machines __-dct float__ is slower
260 than __-dct int__; in this case it is not worth using,
261 because its theoretical accuracy advantage is too small to
262 be significant in practice.
263
264
265 Another program, __djpeg__, is similar. __djpeg__ is
266 maintained by the Independent JPEG Group and packaged with
267 the JPEG library which __jpegtopnm__ uses for all its
268 JPEG work. Because of that, you may expect it to exploit
269 more current JPEG features. Also, since you have to have the
270 library to run __jpegtopnm__, but not vice versa,
271 __cjpeg__ may be more commonly available.
272
273
274 On the other hand, __djpeg__ does not use the NetPBM
275 libraries to generate its output, as all the NetPBM tools
276 such as __jpegtopnm__ do. This means it is less likely to
277 be consistent with all the other programs that deal with the
278 NetPBM formats. Also, the command syntax of __jpegtopnm__
279 is consistent with that of the other Netpbm tools, unlike
280 __djpeg__.
281 !!ENVIRONMENT
282
283
284 __JPEGMEM__
285
286
287 If this environment variable is set, its value is the
288 default memory limit. The value is specified as described
289 for the __-maxmemory__ option. An explicit
290 __-maxmemory__ option overrides any
291 __JPEGMEM__.
292 !!SEE ALSO
293
294
295 ppm(5), pgm(5), ppmtojpeg(1),
296 ppmquant(1), pnmscale(1), ppmtopgm(1),
297 ppmdither(1), pnmdepth(1),__
298 djpeg__(1), cjpeg(1), jpegtran(1),
299 rdjpgcom(1), wrjpgcom(1), jhead(1)
300 Wallace, Gregory K.
301 !!LIMITATIONS
302
303
304 Arithmetic coding is not supported for legal
305 reasons.
306
307
308 The program could be much faster.
309 !!AUTHOR
310
311
312 __jpegtopnm__ and this man page were derived in large
313 part from __djpeg__, by the Independent JPEG Group. The
314 program is otherwise by Bryan Henderson on March 19,
315 2000.
316 ----
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