DRC | ccd1bfd | 2012-01-31 09:53:46 +0000 | [diff] [blame] | 1 | .TH CJPEG 1 "31 January 2012" |
Thomas G. Lane | bd543f0 | 1991-12-13 00:00:00 +0000 | [diff] [blame] | 2 | .SH NAME |
| 3 | cjpeg \- compress an image file to a JPEG file |
| 4 | .SH SYNOPSIS |
| 5 | .B cjpeg |
| 6 | [ |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 7 | .I options |
Thomas G. Lane | 4a6b730 | 1992-03-17 00:00:00 +0000 | [diff] [blame] | 8 | ] |
| 9 | [ |
Thomas G. Lane | bd543f0 | 1991-12-13 00:00:00 +0000 | [diff] [blame] | 10 | .I filename |
| 11 | ] |
| 12 | .LP |
| 13 | .SH DESCRIPTION |
| 14 | .LP |
| 15 | .B cjpeg |
| 16 | compresses the named image file, or the standard input if no file is |
| 17 | named, and produces a JPEG/JFIF file on the standard output. |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 18 | The currently supported input file formats are: PPM (PBMPLUS color |
Thomas G. Lane | 5ead57a | 1998-03-27 00:00:00 +0000 | [diff] [blame] | 19 | format), PGM (PBMPLUS gray-scale format), BMP, Targa, and RLE (Utah Raster |
Thomas G. Lane | bd543f0 | 1991-12-13 00:00:00 +0000 | [diff] [blame] | 20 | Toolkit format). (RLE is supported only if the URT library is available.) |
| 21 | .SH OPTIONS |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 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 |
Thomas G. Lane | 5ead57a | 1998-03-27 00:00:00 +0000 | [diff] [blame] | 30 | .B \-BMP |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 31 | is the same as |
Thomas G. Lane | 5ead57a | 1998-03-27 00:00:00 +0000 | [diff] [blame] | 32 | .BR \-bmp ). |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 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: |
Thomas G. Lane | bd543f0 | 1991-12-13 00:00:00 +0000 | [diff] [blame] | 38 | .TP |
Guido Vollbeding | 5996a25 | 2009-06-27 00:00:00 +0000 | [diff] [blame] | 39 | .BI \-quality " N[,...]" |
Thomas G. Lane | bd543f0 | 1991-12-13 00:00:00 +0000 | [diff] [blame] | 40 | Scale quantization tables to adjust image quality. Quality is 0 (worst) to |
| 41 | 100 (best); default is 75. (See below for more info.) |
| 42 | .TP |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 43 | .B \-grayscale |
| 44 | Create monochrome JPEG file from color input. Be sure to use this switch when |
Thomas G. Lane | 5ead57a | 1998-03-27 00:00:00 +0000 | [diff] [blame] | 45 | compressing a grayscale BMP file, because |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 46 | .B cjpeg |
Thomas G. Lane | 5ead57a | 1998-03-27 00:00:00 +0000 | [diff] [blame] | 47 | isn't bright enough to notice whether a BMP file uses only shades of gray. |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 48 | By saying |
| 49 | .BR \-grayscale , |
| 50 | you'll get a smaller JPEG file that takes less time to process. |
| 51 | .TP |
| 52 | .B \-optimize |
Thomas G. Lane | bd543f0 | 1991-12-13 00:00:00 +0000 | [diff] [blame] | 53 | Perform optimization of entropy encoding parameters. Without this, default |
| 54 | encoding parameters are used. |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 55 | .B \-optimize |
Thomas G. Lane | bd543f0 | 1991-12-13 00:00:00 +0000 | [diff] [blame] | 56 | usually makes the JPEG file a little smaller, but |
| 57 | .B cjpeg |
Thomas G. Lane | 4a6b730 | 1992-03-17 00:00:00 +0000 | [diff] [blame] | 58 | runs somewhat slower and needs much more memory. Image quality and speed of |
| 59 | decompression are unaffected by |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 60 | .BR \-optimize . |
Thomas G. Lane | bd543f0 | 1991-12-13 00:00:00 +0000 | [diff] [blame] | 61 | .TP |
Thomas G. Lane | bc79e06 | 1995-08-02 00:00:00 +0000 | [diff] [blame] | 62 | .B \-progressive |
| 63 | Create progressive JPEG file (see below). |
| 64 | .TP |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 65 | .B \-targa |
Thomas G. Lane | bd543f0 | 1991-12-13 00:00:00 +0000 | [diff] [blame] | 66 | Input file is Targa format. Targa files that contain an "identification" |
| 67 | field will not be automatically recognized by |
| 68 | .BR cjpeg ; |
| 69 | for such files you must specify |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 70 | .B \-targa |
| 71 | to make |
Thomas G. Lane | bd543f0 | 1991-12-13 00:00:00 +0000 | [diff] [blame] | 72 | .B cjpeg |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 73 | treat the input as Targa format. |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 74 | For most Targa files, you won't need this switch. |
Thomas G. Lane | bd543f0 | 1991-12-13 00:00:00 +0000 | [diff] [blame] | 75 | .PP |
| 76 | The |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 77 | .B \-quality |
Thomas G. Lane | bd543f0 | 1991-12-13 00:00:00 +0000 | [diff] [blame] | 78 | switch lets you trade off compressed file size against quality of the |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 79 | reconstructed image: the higher the quality setting, the larger the JPEG file, |
| 80 | and the closer the output image will be to the original input. Normally you |
| 81 | want to use the lowest quality setting (smallest file) that decompresses into |
| 82 | something visually indistinguishable from the original image. For this |
| 83 | purpose the quality setting should be between 50 and 95; the default of 75 is |
| 84 | often about right. If you see defects at |
| 85 | .B \-quality |
Thomas G. Lane | bd543f0 | 1991-12-13 00:00:00 +0000 | [diff] [blame] | 86 | 75, then go up 5 or 10 counts at a time until you are happy with the output |
| 87 | image. (The optimal setting will vary from one image to another.) |
| 88 | .PP |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 89 | .B \-quality |
Thomas G. Lane | bc79e06 | 1995-08-02 00:00:00 +0000 | [diff] [blame] | 90 | 100 will generate a quantization table of all 1's, minimizing loss in the |
Thomas G. Lane | bd543f0 | 1991-12-13 00:00:00 +0000 | [diff] [blame] | 91 | quantization step (but there is still information loss in subsampling, as well |
| 92 | as roundoff error). This setting is mainly of interest for experimental |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 93 | purposes. Quality values above about 95 are |
Thomas G. Lane | bd543f0 | 1991-12-13 00:00:00 +0000 | [diff] [blame] | 94 | .B not |
| 95 | recommended for normal use; the compressed file size goes up dramatically for |
| 96 | hardly any gain in output image quality. |
| 97 | .PP |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 98 | In the other direction, quality values below 50 will produce very small files |
| 99 | of low image quality. Settings around 5 to 10 might be useful in preparing an |
| 100 | index of a large image library, for example. Try |
| 101 | .B \-quality |
| 102 | 2 (or so) for some amusing Cubist effects. (Note: quality |
Thomas G. Lane | bd543f0 | 1991-12-13 00:00:00 +0000 | [diff] [blame] | 103 | values below about 25 generate 2-byte quantization tables, which are |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 104 | considered optional in the JPEG standard. |
Thomas G. Lane | bd543f0 | 1991-12-13 00:00:00 +0000 | [diff] [blame] | 105 | .B cjpeg |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 106 | emits a warning message when you give such a quality value, because some |
Thomas G. Lane | bc79e06 | 1995-08-02 00:00:00 +0000 | [diff] [blame] | 107 | other JPEG programs may be unable to decode the resulting file. Use |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 108 | .B \-baseline |
| 109 | if you need to ensure compatibility at low quality values.) |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 110 | .PP |
DRC | 39ea562 | 2010-10-12 01:55:31 +0000 | [diff] [blame] | 111 | The \fB-quality\fR option has been extended in this version of \fBcjpeg\fR to |
| 112 | support separate quality settings for luminance and chrominance (or, in |
| 113 | general, separate settings for every quantization table slot.) The principle |
| 114 | is the same as chrominance subsampling: since the human eye is more sensitive |
| 115 | to spatial changes in brightness than spatial changes in color, the chrominance |
| 116 | components can be quantized more than the luminance components without |
| 117 | incurring any visible image quality loss. However, unlike subsampling, this |
| 118 | feature reduces data in the frequency domain instead of the spatial domain, |
| 119 | which allows for more fine-grained control. This option is useful in |
| 120 | quality-sensitive applications, for which the artifacts generated by |
| 121 | subsampling may be unacceptable. |
| 122 | .PP |
| 123 | The \fB-quality\fR option accepts a comma-separated list of parameters, which |
DRC | ccd1bfd | 2012-01-31 09:53:46 +0000 | [diff] [blame] | 124 | respectively refer to the quality levels that should be assigned to the |
DRC | 39ea562 | 2010-10-12 01:55:31 +0000 | [diff] [blame] | 125 | quantization table slots. If there are more q-table slots than parameters, |
| 126 | then the last parameter is replicated. Thus, if only one quality parameter is |
| 127 | given, this is used for both luminance and chrominance (slots 0 and 1, |
| 128 | respectively), preserving the legacy behavior of cjpeg v6b and prior. |
| 129 | More (or customized) quantization tables can be set with the \fB-qtables\fR |
| 130 | option and assigned to components with the \fB-qslots\fR option (see the |
| 131 | "wizard" switches below.) |
| 132 | .PP |
| 133 | JPEG files generated with separate luminance and chrominance quality are fully |
| 134 | compliant with standard JPEG decoders. |
| 135 | .PP |
| 136 | .BR CAUTION: |
| 137 | For this setting to be useful, be sure to pass an argument of \fB-sample 1x1\fR |
| 138 | to \fBcjpeg\fR to disable chrominance subsampling. Otherwise, the default |
| 139 | subsampling level (2x2, AKA "4:2:0") will be used. |
Guido Vollbeding | 5996a25 | 2009-06-27 00:00:00 +0000 | [diff] [blame] | 140 | .PP |
| 141 | The |
Thomas G. Lane | bc79e06 | 1995-08-02 00:00:00 +0000 | [diff] [blame] | 142 | .B \-progressive |
| 143 | switch creates a "progressive JPEG" file. In this type of JPEG file, the data |
| 144 | is stored in multiple scans of increasing quality. If the file is being |
| 145 | transmitted over a slow communications link, the decoder can use the first |
| 146 | scan to display a low-quality image very quickly, and can then improve the |
| 147 | display with each subsequent scan. The final image is exactly equivalent to a |
| 148 | standard JPEG file of the same quality setting, and the total file size is |
| 149 | about the same --- often a little smaller. |
Thomas G. Lane | bc79e06 | 1995-08-02 00:00:00 +0000 | [diff] [blame] | 150 | .PP |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 151 | Switches for advanced users: |
| 152 | .TP |
DRC | d657ba6 | 2012-01-27 09:41:20 +0000 | [diff] [blame] | 153 | .B \-arithmetic |
| 154 | Use arithmetic coding. |
| 155 | .B Caution: |
| 156 | arithmetic coded JPEG is not yet widely implemented, so many decoders will be |
| 157 | unable to view an arithmetic coded JPEG file at all. |
| 158 | .TP |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 159 | .B \-dct int |
| 160 | Use integer DCT method (default). |
| 161 | .TP |
| 162 | .B \-dct fast |
| 163 | Use fast integer DCT (less accurate). |
| 164 | .TP |
| 165 | .B \-dct float |
| 166 | Use floating-point DCT method. |
Thomas G. Lane | a8b67c4 | 1995-03-15 00:00:00 +0000 | [diff] [blame] | 167 | The float method is very slightly more accurate than the int method, but is |
| 168 | much slower unless your machine has very fast floating-point hardware. Also |
| 169 | note that results of the floating-point method may vary slightly across |
| 170 | machines, while the integer methods should give the same results everywhere. |
| 171 | The fast integer method is much less accurate than the other two. |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 172 | .TP |
| 173 | .BI \-restart " N" |
| 174 | Emit a JPEG restart marker every N MCU rows, or every N MCU blocks if "B" is |
| 175 | attached to the number. |
| 176 | .B \-restart 0 |
| 177 | (the default) means no restart markers. |
| 178 | .TP |
| 179 | .BI \-smooth " N" |
| 180 | Smooth the input image to eliminate dithering noise. N, ranging from 1 to |
| 181 | 100, indicates the strength of smoothing. 0 (the default) means no smoothing. |
| 182 | .TP |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 183 | .BI \-maxmemory " N" |
| 184 | Set limit for amount of memory to use in processing large images. Value is |
| 185 | in thousands of bytes, or millions of bytes if "M" is attached to the |
| 186 | number. For example, |
| 187 | .B \-max 4m |
| 188 | selects 4000000 bytes. If more space is needed, temporary files will be used. |
| 189 | .TP |
| 190 | .BI \-outfile " name" |
| 191 | Send output image to the named file, not to standard output. |
| 192 | .TP |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 193 | .B \-verbose |
| 194 | Enable debug printout. More |
| 195 | .BR \-v 's |
| 196 | give more output. Also, version information is printed at startup. |
| 197 | .TP |
| 198 | .B \-debug |
| 199 | Same as |
| 200 | .BR \-verbose . |
| 201 | .PP |
| 202 | The |
| 203 | .B \-restart |
| 204 | option inserts extra markers that allow a JPEG decoder to resynchronize after |
| 205 | a transmission error. Without restart markers, any damage to a compressed |
| 206 | file will usually ruin the image from the point of the error to the end of the |
| 207 | image; with restart markers, the damage is usually confined to the portion of |
| 208 | the image up to the next restart marker. Of course, the restart markers |
| 209 | occupy extra space. We recommend |
| 210 | .B \-restart 1 |
| 211 | for images that will be transmitted across unreliable networks such as Usenet. |
| 212 | .PP |
| 213 | The |
| 214 | .B \-smooth |
| 215 | option filters the input to eliminate fine-scale noise. This is often useful |
Thomas G. Lane | 5ead57a | 1998-03-27 00:00:00 +0000 | [diff] [blame] | 216 | when converting dithered images to JPEG: a moderate smoothing factor of 10 to |
| 217 | 50 gets rid of dithering patterns in the input file, resulting in a smaller |
| 218 | JPEG file and a better-looking image. Too large a smoothing factor will |
| 219 | visibly blur the image, however. |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 220 | .PP |
| 221 | Switches for wizards: |
| 222 | .TP |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 223 | .B \-baseline |
Thomas G. Lane | 5ead57a | 1998-03-27 00:00:00 +0000 | [diff] [blame] | 224 | Force baseline-compatible quantization tables to be generated. This clamps |
| 225 | quantization values to 8 bits even at low quality settings. (This switch is |
| 226 | poorly named, since it does not ensure that the output is actually baseline |
| 227 | JPEG. For example, you can use |
| 228 | .B \-baseline |
| 229 | and |
| 230 | .B \-progressive |
| 231 | together.) |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 232 | .TP |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 233 | .BI \-qtables " file" |
Thomas G. Lane | bc79e06 | 1995-08-02 00:00:00 +0000 | [diff] [blame] | 234 | Use the quantization tables given in the specified text file. |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 235 | .TP |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 236 | .BI \-qslots " N[,...]" |
Thomas G. Lane | bc79e06 | 1995-08-02 00:00:00 +0000 | [diff] [blame] | 237 | Select which quantization table to use for each color component. |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 238 | .TP |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 239 | .BI \-sample " HxV[,...]" |
Thomas G. Lane | bc79e06 | 1995-08-02 00:00:00 +0000 | [diff] [blame] | 240 | Set JPEG sampling factors for each color component. |
| 241 | .TP |
| 242 | .BI \-scans " file" |
| 243 | Use the scan script given in the specified text file. |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 244 | .PP |
| 245 | The "wizard" switches are intended for experimentation with JPEG. If you |
Thomas G. Lane | bc79e06 | 1995-08-02 00:00:00 +0000 | [diff] [blame] | 246 | don't know what you are doing, \fBdon't use them\fR. These switches are |
Guido Vollbeding | 5996a25 | 2009-06-27 00:00:00 +0000 | [diff] [blame] | 247 | documented further in the file wizard.txt. |
Thomas G. Lane | bd543f0 | 1991-12-13 00:00:00 +0000 | [diff] [blame] | 248 | .SH EXAMPLES |
| 249 | .LP |
| 250 | This example compresses the PPM file foo.ppm with a quality factor of |
| 251 | 60 and saves the output as foo.jpg: |
| 252 | .IP |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 253 | .B cjpeg \-quality |
Thomas G. Lane | bd543f0 | 1991-12-13 00:00:00 +0000 | [diff] [blame] | 254 | .I 60 foo.ppm |
| 255 | .B > |
| 256 | .I foo.jpg |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 257 | .SH HINTS |
| 258 | Color GIF files are not the ideal input for JPEG; JPEG is really intended for |
| 259 | compressing full-color (24-bit) images. In particular, don't try to convert |
| 260 | cartoons, line drawings, and other images that have only a few distinct |
| 261 | colors. GIF works great on these, JPEG does not. If you want to convert a |
| 262 | GIF to JPEG, you should experiment with |
| 263 | .BR cjpeg 's |
| 264 | .B \-quality |
| 265 | and |
| 266 | .B \-smooth |
| 267 | options to get a satisfactory conversion. |
| 268 | .B \-smooth 10 |
| 269 | or so is often helpful. |
| 270 | .PP |
| 271 | Avoid running an image through a series of JPEG compression/decompression |
| 272 | cycles. Image quality loss will accumulate; after ten or so cycles the image |
| 273 | may be noticeably worse than it was after one cycle. It's best to use a |
| 274 | lossless format while manipulating an image, then convert to JPEG format when |
| 275 | you are ready to file the image away. |
| 276 | .PP |
| 277 | The |
| 278 | .B \-optimize |
| 279 | option to |
| 280 | .B cjpeg |
| 281 | is worth using when you are making a "final" version for posting or archiving. |
| 282 | It's also a win when you are using low quality settings to make very small |
| 283 | JPEG files; the percentage improvement is often a lot more than it is on |
Thomas G. Lane | bc79e06 | 1995-08-02 00:00:00 +0000 | [diff] [blame] | 284 | larger files. (At present, |
| 285 | .B \-optimize |
| 286 | mode is always selected when generating progressive JPEG files.) |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 287 | .SH ENVIRONMENT |
| 288 | .TP |
| 289 | .B JPEGMEM |
| 290 | If this environment variable is set, its value is the default memory limit. |
| 291 | The value is specified as described for the |
| 292 | .B \-maxmemory |
| 293 | switch. |
| 294 | .B JPEGMEM |
| 295 | overrides the default value specified when the program was compiled, and |
| 296 | itself is overridden by an explicit |
| 297 | .BR \-maxmemory . |
Thomas G. Lane | bd543f0 | 1991-12-13 00:00:00 +0000 | [diff] [blame] | 298 | .SH SEE ALSO |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 299 | .BR djpeg (1), |
Thomas G. Lane | bc79e06 | 1995-08-02 00:00:00 +0000 | [diff] [blame] | 300 | .BR jpegtran (1), |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 301 | .BR rdjpgcom (1), |
| 302 | .BR wrjpgcom (1) |
Thomas G. Lane | bd543f0 | 1991-12-13 00:00:00 +0000 | [diff] [blame] | 303 | .br |
Thomas G. Lane | 4a6b730 | 1992-03-17 00:00:00 +0000 | [diff] [blame] | 304 | .BR ppm (5), |
| 305 | .BR pgm (5) |
| 306 | .br |
Thomas G. Lane | bd543f0 | 1991-12-13 00:00:00 +0000 | [diff] [blame] | 307 | Wallace, Gregory K. "The JPEG Still Picture Compression Standard", |
| 308 | Communications of the ACM, April 1991 (vol. 34, no. 4), pp. 30-44. |
| 309 | .SH AUTHOR |
| 310 | Independent JPEG Group |
| 311 | .SH BUGS |
DRC | 39ea562 | 2010-10-12 01:55:31 +0000 | [diff] [blame] | 312 | Support for GIF input files was removed in cjpeg v6b due to concerns over |
| 313 | the Unisys LZW patent. Although this patent expired in 2006, cjpeg still |
| 314 | lacks GIF support, for these historical reasons. (Conversion of GIF files to |
| 315 | JPEG is usually a bad idea anyway.) |
Thomas G. Lane | 5ead57a | 1998-03-27 00:00:00 +0000 | [diff] [blame] | 316 | .PP |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 317 | Not all variants of BMP and Targa file formats are supported. |
Thomas G. Lane | bd543f0 | 1991-12-13 00:00:00 +0000 | [diff] [blame] | 318 | .PP |
| 319 | The |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 320 | .B \-targa |
Thomas G. Lane | bd543f0 | 1991-12-13 00:00:00 +0000 | [diff] [blame] | 321 | switch is not a bug, it's a feature. (It would be a bug if the Targa format |
| 322 | designers had not been clueless.) |