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| author | giraffedata <giraffedata@9d0c8265-081b-0410-96cb-a4ca84ce46f8> | 2006-12-25 03:06:05 +0000 |
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| committer | giraffedata <giraffedata@9d0c8265-081b-0410-96cb-a4ca84ce46f8> | 2006-12-25 03:06:05 +0000 |
| commit | 1017cbebe5d5edd859e0fddad0a8600f509f4821 (patch) | |
| tree | 78bdf336648566f7a7d55f42837357dea3dd674c /jpegtopnm.html | |
| parent | 16f2ac126651015a376eba864a3a35f738b0b25a (diff) | |
| download | netpbm-mirror-1017cbebe5d5edd859e0fddad0a8600f509f4821.tar.gz netpbm-mirror-1017cbebe5d5edd859e0fddad0a8600f509f4821.tar.xz netpbm-mirror-1017cbebe5d5edd859e0fddad0a8600f509f4821.zip | |
Place user guide into Subversion repository
git-svn-id: http://svn.code.sf.net/p/netpbm/code/userguide@181 9d0c8265-081b-0410-96cb-a4ca84ce46f8
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diff --git a/jpegtopnm.html b/jpegtopnm.html new file mode 100644 index 00000000..86a44d50 --- /dev/null +++ b/jpegtopnm.html @@ -0,0 +1,339 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.2//EN"> +<HTML><HEAD><TITLE>Jpegtopnm User Manual</TITLE></HEAD> +<BODY> +<H1>JPEGTOPNM</H1> +Updated: 13 October 2002 +<BR> +<A HREF="#index">Table Of Contents</A> + +<A NAME="lbAB"> </A> +<H2>NAME</H2> +jpegtopnm - convert JPEG/JFIF file to PPM or PGM image + +<A NAME="lbAC"> </A> +<H2>SYNOPSIS</H2> + +<B>jpegtopnm</B> +[<B>-dct</B> {<B>int</B>|<B>fast</B>|<B>float</B>}] +[<B>-nosmooth</B>] +[<B>-maxmemory</B> <I>N</I>] +[{<B>-adobe</B>|<B>-notadobe</B>}] +[<B>-comments</B>] +[<B>-dumpexif</B>] +[<B>-exif=</B><I>filespec</I>] +[<B>-multiple</B>] +[<B>-verbose</B>] +[<B>-tracelevel</B> <I>N</I>] +[<I>filename</I>] + +<p>Minimum unique abbreviation of option is acceptable. You may use double +hyphens instead of single hyphen to denote options. You may use white +space in place of the equals sign to separate an option name from its value. + +<A NAME="description"> </A> +<H2>DESCRIPTION</H2> + +<p>This program is part of <a href="index.html">Netpbm</a>. + +<P><B>jpegtopnm</B> converts JFIF images to PPM or PGM images. + +<p>By default, <b>jpegtopnm</b> expects the input stream to contain one +JFIF image and produces one PGM or PPM image as output. It fails if the +input stream is empty. + +<p>But with the <b>-multiple</b> option, <b>jpegtopnm</b> reads JFIF +images sequentially from the input stream and writes one PPM or PGM image +to the output stream for each JFIF input. If the input stream is empty, +so is the output. + +<p>The input stream is the <i>filename</i> you specify or, if you +don't specify <i>filename</i>, Standard Input. The output stream is +Standard Output. + +<p>If a JFIF input image is of the grayscale variety, <B>jpegtopnm</B> +generates a PGM image. Otherwise, it generates a PPM image. + +<p>Before Netpbm 10.11 (October 2002), <b>jpegtopnm</b> did not have +the multiple image stream capability. From 10.11 through 10.22, +Netpbm always behaved as if you specified <b>-multiple</b>. Starting +with Netpbm 10.23 (July 2004), Netpbm's default behavior went back to +the pre-10.11 behavior and the new <b>-multiple</b> option selected +the 10.12 behavior. The reason for the reversion was that there were +discovered in the world files that contain JFIF images followed by +something other than another JFIF image. The producers of these files +expect them to work with any JFIF interpreter because most JFIF +interpreters just stop reading the file after the first JFIF image. + +<p><B>jpegtopnm</B> uses the Independent JPEG Group's JPEG library to +interpret the input file. See <B><A +HREF="http://www.ijg.org">http://www.ijg.org</A> </B> +for information on the library. + +<P>"JFIF" is the correct name for the image format commonly +known as "JPEG." Strictly speaking, JPEG is a method of +compression. The image format using JPEG compression that is by far +the most common is JFIF. There is also a subformat of TIFF that uses +JPEG compression. + +<P>EXIF is an image format that is a subformat of JFIF (to wit, a JFIF +file that contains an EXIF header as an APP1 marker). +<B>jpegtopnm</B> handles EXIF. + +<P>JFIF files can have either 8 bits per sample or 12 bits per sample. +The 8 bit variety is by far the most common. There are two versions +of the IJG JPEG library. One reads only 8 bit files and the other +reads only 12 bit files. You must link the appropriate one of these +libraries with <B>jpegtopnm</B>. Ordinarily, this means the library +is in your shared library search path when you run <B>jpegtopnm</B>. + +<P><B>jpegtopnm</B> generates output with either one byte or two bytes +per sample depending on whether the JFIF input has either 8 bits or 12 +bits per sample. You can use <B>pamdepth</B> to reduce a +two-byte-per-sample file to a one-byte-per-sample file if you need to. + +<P>If the JFIF file uses the CMYK or YCCK color space, the input does +not actually contain enough information to know what color each pixel +is. To know what color a pixel is, one would have to know the +properties of the inks to which the color space refers. +<B>jpegtopnm</B> interprets the colors using the common transformation +which assumes all the inks are simply subtractive and linear. + +<p>See the <a href="jpegtopnm.html"><B>jpegtopnm</B> manual</a> +for information on how images lose quality when you convert to and +from JFIF. + +<A NAME="lbAE"> </A> +<H2>OPTIONS</H2> + +The options are only for advanced users: +<DL COMPACT> +<DT><B>-dct int</B> + +<DD> +Use integer DCT method (default). + +<DT><B>-dct fast</B> + +<DD> +Use fast integer DCT (less accurate). + +<DT><B>-dct float</B> + +<DD> +Use floating-point DCT method. +The float method is very slightly more accurate than the int method, but is +much slower unless your machine has very fast floating-point hardware. Also +note that results of the floating-point method may vary slightly across +machines, while the integer methods should give the same results everywhere. +The fast integer method is much less accurate than the other two. + +<DT><B>-nosmooth</B> + +<DD> +Use a faster, lower-quality upsampling routine. +<DT><B>-maxmemory</B><I> N</I> + +<DD>Set limit on the amount of memory <B>jpegtopnm</B> uses in +processing large images. Value is in thousands of bytes, or millions +of bytes if "M" is suffixed to the number. For example, +<B>-maxmemory 4m</B> selects 4000000 bytes. If <B>jpegtopnm</B> needs +more space, it uses temporary files. + +<DT><B>-adobe</B> +<DT><B>-notadobe</B> + +<DD> +There are two variations on the CMYK (and likewise YCCK) color space that +may be used in the JFIF input. In the normal one, a zero value for a color +components indicates absence of ink. In the other, a zero value means the +maximum ink coverage. The latter is used by Adobe Photoshop when it creates +a bare JFIF output file (but not when it creates JFIF output as part of +Encapsulated Postscript output). + +<P>These options tell <B>jpegtopnm</B> which version of the CMYK or +YCCK color space the image uses. If you specify neither, +<B>jpegtopnm</B> tries to figure it out on its own. In the present +version, it doesn't try very hard at all: It just assumes the +Photoshop version, since Photoshop and its emulators seem to be the +main source of CMYK and YCCK images. But with experience of use, +future versions might be more sophisticated. + +<P>If the JFIF image does not indicate that it is CMYK or YCCK, these +options have no effect. + +<P>If you don't use the right one of these options, the symptom is +output that looks like a negative. + +<DT><B>-dumpexif</B> + +<DD>Print the interpreted contents of any Exif header in the input +file to the Standard Error file. Similar to the program <B>jhead</B> +(not part of the Netpbm package). + +<p>This option was added in Netpbm 9.19 (September 2001). + +<DT><B>-exif=</B><I>filespec</I> + +<DD>Extract the contents of the EXIF header from the input image and +write it to the file <I>filespec</I>. <I>filespec</I>=<B>-</B> means +write it to Standard Output. When you write the EXIF header to +Standard Output, <B>jpegtopnm</B> does not output the converted image +(which is what normally would go to Standard Output) at all. + +<p><B>jpegtopnm</B> writes the contents of the EXIF header +byte-for-byte, starting with the two byte length field (which length +includes those two bytes). + +<P>You can use this file as input to <B>pnmtojpeg</B> to insert an +identical EXIF header into a new JFIF image. + +<P>If there is no EXIF header, <B>jpegtopnm</B> writes two bytes of +binary zero and nothing else. + +<P>An EXIF header takes the form of a JFIF APP1 marker. Only the +first such marker within the JFIF header counts. + +<p>This option was added in Netpbm 9.19 (September 2001). + +<DT><B>-multiple</B> + +<dd>Read multiple JFIF images sequentially from the input stream. +See <a href="#description">Description section</a> for details. + +<p>This option was new in Netpbm 10.23 (July 2004). + +<DT><B>-comments</B> + +<DD> +Print any comments in the input file to the Standard Error file. +<DT><B>-verbose</B> + +<DD> +Print details about the conversion to the Standard Error file. +<DT><B>-tracelevel</B><I> n</I> + +<DD>Turn on the JPEG library's trace messages to the Standard Error +file. A higher value of <I>n</I> gets more trace information. +<B>-verbose</B> implies a trace level of at least 1. + +</DL> +<A NAME="lbAF"> </A> +<H2>EXAMPLES</H2> + +<P>This example converts the color JFIF file foo.jpg to a PPM file +named foo.ppm: + +<PRE> + jpegtopnm foo.jpg >foo.ppm +</PRE> + +<A NAME="lbAG"> </A> +<H2>HINTS</H2> + +You can use <B>pnmquant</B> to color quantize the result, i.e. to +reduce the number of distinct colors in the image. In fact, you may +have to if you want to convert the PPM file to certain other formats. +<B>ppmdither</B> Does a more sophisticated quantization. + +<p>Use <B>pamscale</B> to change the dimensions of the resulting +image. + +<P>Use <B>ppmtopgm </B> to convert a color JFIF file to a grayscale +PGM file. + +<P>You can easily use these converters together. E.g.: + +<PRE> + jpegtopnm foo.jpg | ppmtopgm | pamscale .25 >foo.pgm +</PRE> + +<P><B>-dct fast</B> and/or <B>-nosmooth</B> gain speed at a small +sacrifice in quality. + +<P>If you are fortunate enough to have very fast floating point +hardware, <B>-dct float</B> may be even faster than <B>-dct fast</B>. +But on most machines <B>-dct float</B> is slower than <B>-dct int</B>; +in this case it is not worth using, because its theoretical accuracy +advantage is too small to be significant in practice. + +<P>Another program, <B>djpeg</B>, is similar. <B>djpeg</B> is +maintained by the Independent JPEG Group and packaged with the JPEG +library which <B>jpegtopnm</B> uses for all its JPEG work. Because of +that, you may expect it to exploit more current JPEG features. Also, +since you have to have the library to run <B>jpegtopnm</B>, but not +vice versa, <B>cjpeg</B> may be more commonly available. + +<P>On the other hand, <B>djpeg</B> does not use the NetPBM libraries +to generate its output, as all the NetPBM tools such as +<B>jpegtopnm</B> do. This means it is less likely to be consistent +with all the other programs that deal with the NetPBM formats. Also, +the command syntax of <B>jpegtopnm</B> is consistent with that of the +other Netpbm tools, unlike <B>djpeg</B>. + +<A NAME="lbAH"> </A> +<H2>ENVIRONMENT</H2> + +<DL COMPACT> +<DT><B>JPEGMEM</B> + +<DD>If this environment variable is set, its value is the default +memory limit. The value is specified as described for the +<B>-maxmemory</B> option. An explicit <B>-maxmemory </B> option +overrides any <B>JPEGMEM</B>. + +</DL> + +<A NAME="lbAI"> </A> +<H2>SEE ALSO</H2> + +<p> +<B><A HREF="ppm.html">ppm</A></B>, +<B><A HREF="pgm.html">pgm</A></B>, +<B><A HREF="pnmtojpeg.html">pnmtojpeg</A></B>, +<B><A HREF="pnmquant.html">pnmquant</A></B>, +<B><A HREF="pamscale.html">pamscale</A></B>, +<B><A HREF="ppmtopgm.html">ppmtopgm</A></B>, +<B><A HREF="ppmdither.html">ppmdither</A></B>, +<B><A HREF="pamdepth.html">pamdepth</A></B>, + +<p> +<B>djpeg</B> man page, +<B>cjpeg</B> man page, +<B>jpegtran</B> man page, +<B>rdjpgcom</B> man page, +<B>wrjpgcom</B> man page, +<B>jhead</B> man page + +<p>Wallace, Gregory K. "The JPEG Still Picture Compression +Standard", Communications of the ACM, April 1991 (vol. 34, +no. 4), pp. 30-44. + +<A NAME="lbAJ"> </A> +<H2>LIMITATIONS</H2> + +<p>Arithmetic coding is not offered for legal reasons. The program +could be much faster. + +<A NAME="lbAK"> </A> +<H2>AUTHOR</H2> + +<p><B>jpegtopnm</B> and this manual were derived in large part from +<B>djpeg</B>, by the Independent JPEG Group. The program is otherwise +by Bryan Henderson on March 19, 2000. + +<HR> +<A NAME="index"> </A><H2>Table Of Contents</H2> +<UL> +<LI><A HREF="#lbAB">NAME</A> +<LI><A HREF="#lbAC">SYNOPSIS</A> +<LI><A HREF="#description">DESCRIPTION</A> +<LI><A HREF="#lbAE">OPTIONS</A> +<LI><A HREF="#lbAF">EXAMPLES</A> +<LI><A HREF="#lbAG">HINTS</A> +<LI><A HREF="#lbAH">ENVIRONMENT</A> +<LI><A HREF="#lbAI">SEE ALSO</A> +<LI><A HREF="#lbAJ">LIMITATIONS</A> +<LI><A HREF="#lbAK">AUTHOR</A> +</UL> +</BODY> +</HTML> |