| <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" |
| "http://www.w3.org/TR/html4/loose.dtd"> |
| <html > |
| <head><title>Introduction</title> |
| <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> |
| <meta name="generator" content="TeX4ht (http://www.cse.ohio-state.edu/~gurari/TeX4ht/)"> |
| <meta name="originator" content="TeX4ht (http://www.cse.ohio-state.edu/~gurari/TeX4ht/)"> |
| <!-- 3,html --> |
| <meta name="src" content="vipsmanual.tex"> |
| <meta name="date" content="2010-06-09 21:39:00"> |
| <link rel="stylesheet" type="text/css" href="vipsmanual.css"> |
| </head><body |
| > |
| <!--l. 1--><div class="crosslinks"><p class="noindent">[<a |
| href="vipsmanualse14.html" >next</a>] [<a |
| href="#tailvipsmanualse13.html">tail</a>] [<a |
| href="vipsmanualch3.html#vipsmanualse13.html" >up</a>] </p></div> |
| <h3 class="sectionHead"><span class="titlemark">3.1 </span> <a |
| id="x20-850003.1"></a>Introduction</h3> |
| <!--l. 2--><p class="noindent" ><a name="nip_label_sec:oper"></a> |
| <!--l. 4--><p class="indent" > This chapter explains how to write image processing |
| operations using the VIPS image I/O (input-output) system. |
| For background, you should probably take a look at <span |
| class="cmsy-10">§</span><a |
| href="vipsmanualse7.html#x13-360002.1">2.1<!--tex4ht:ref: sec:appl --></a>. |
| This is supposed to be a tutorial, if you need detailed |
| information on any particular function, use the on-line |
| UNIX manual pages. |
| <!--l. 10--><p class="noindent" > |
| <h4 class="subsectionHead"><span class="titlemark">3.1.1 </span> <a |
| id="x20-860003.1.1"></a>Why use VIPS?</h4> |
| <!--l. 12--><p class="noindent" >If you use the VIPS image I/O system, you get a number of |
| benefits: |
| <dl class="description"><dt class="description"> |
| <span |
| class="ptmb7t-">Threading</span> </dt><dd |
| class="description">If your computer has more than one CPU, |
| the VIPS I/O system will automatically split your |
| image processing operation into separate threads |
| (provided you use PIO, see below). You should get |
| an approximately linear speed-up as you add more |
| CPUs. </dd><dt class="description"> |
| <span |
| class="ptmb7t-">Pipelining</span> </dt><dd |
| class="description">Provided you use PIO (again, see below), |
| VIPS can automatically join operations together. A |
| sequence of image processing operations will all |
| execute together, with image data flowing through |
| the processing pipeline in small pieces. This makes |
| it possible to perform complex processing on very |
| large images with no need to worry about storage |
| management. |
| </dd><dt class="description"> |
| <span |
| class="ptmb7t-">Composition</span> </dt><dd |
| class="description">Because VIPS can efficiently compose |
| image processing operations, you can |
| implement your new operation in small, reusable, |
| easy-to-understand pieces. VIPS already has a lot |
| of these: many new operations can be implemented |
| by simply composing existing operations. |
| </dd><dt class="description"> |
| <span |
| class="ptmb7t-">Large files</span> </dt><dd |
| class="description">Provided you use PIO and as long as the |
| underlying OS supports large files (that is, files |
| larger than 2GB), VIPS operations can work on |
| files larger than can be addressed with 32 bits on a |
| plain 32-bit machine. VIPS operations only see 32 |
| bit addresses; the VIPS I/O system transparently |
| maps these to 64 bit operations for I/O. Large file |
| support is included on most machines after about |
| 1998. |
| </dd><dt class="description"> |
| <span |
| class="ptmb7t-">Abstraction</span> </dt><dd |
| class="description">VIPS operations see only arrays of |
| numbers in native format. Details of representation |
| (big/little endian, VIPS/TIFF/JPEG file format, |
| etc.) are hidden from you. |
| </dd><dt class="description"> |
| <span |
| class="ptmb7t-">Interfaces</span> </dt><dd |
| class="description">Once you have your image processing |
| operation implemented, it automatically appears in |
| all of the VIPS interfaces. VIPS comes with a GUI |
| (<span |
| class="pcrr7t-">nip2</span>), a UNIX command-line interface (<span |
| class="pcrr7t-">vips</span>) |
| and a C++ and Python API. |
| </dd><dt class="description"> |
| <span |
| class="ptmb7t-">Portability</span> </dt><dd |
| class="description">VIPS operations can be compiled on most |
| unixes, Mac OS X and Windows NT, 2000 and XP |
| without modification. Mostly. |
| </dd></dl> |
| |
| |
| |
| <!--l. 59--><p class="noindent" > |
| <h4 class="subsectionHead"><span class="titlemark">3.1.2 </span> <a |
| id="x20-870003.1.2"></a>I/O styles</h4> |
| <!--l. 61--><p class="noindent" >The I/O system supports three styles of input-output. |
| <dl class="description"><dt class="description"> |
| <span |
| class="ptmb7t-">Whole-image I/O (WIO)</span> </dt><dd |
| class="description">This style is a largely a |
| left-over from VIPS 6.x. WIO image-processing |
| operations have all of the input image given to |
| them in a large memory array. They can read |
| any of the input pels at will with simple pointer |
| arithmetic. |
| </dd><dt class="description"> |
| <span |
| class="ptmb7t-">Partial-image I/O (PIO)</span> </dt><dd |
| class="description">In this style operations only |
| have a small part of the input image available to |
| them at any time. When PIO operations are joined |
| together into a pipeline, images flow through them |
| in small pieces, with all the operations in a pipeline |
| executing at the same time. |
| </dd><dt class="description"> |
| <span |
| class="ptmb7t-">In-place</span> </dt><dd |
| class="description">The third style allows pels to be read and |
| written anywhere in the image at any time, and |
| is used by the VIPS in-place operations, such |
| as <span class="obeylines-h"><span class="verb"><span |
| class="pcrr7t-">im_fastline()</span></span></span>. You should only use it |
| for operations which would just be impossibly |
| inefficient to write with either of the other two |
| styles. |
| </dd></dl> |
| <!--l. 85--><p class="indent" > WIO operations are easy to program, but slow and |
| inflexible when images become large. PIO operations are |
| harder to program, but scale well as images become larger, |
| and are automatically parallelized by the VIPS I/O |
| system. |
| <!--l. 89--><p class="indent" > If you can face it, and if your algorithm can be expressed |
| in this way, you should write your operations using PIO. |
| Whichever you choose, applications which call your |
| operation will see no difference, except in execution |
| speed. |
| <!--l. 93--><p class="indent" > If your image processing operation performs no |
| coordinate transformations, that is, if your output image is |
| the same size as your input image or images, and if |
| each output pixel depends only upon the pixel at the |
| corresponding position in the input images, then you |
| can use the <span class="obeylines-h"><span class="verb"><span |
| class="pcrr7t-">im_wrapone()</span></span></span> and <span class="obeylines-h"><span class="verb"><span |
| class="pcrr7t-">im_wrapmany()</span></span></span> |
| operations. These take a simple buffer-processing operation |
| supplied by you and wrap it up as a full-blown PIO |
| operation. See <span |
| class="cmsy-10">§</span><a |
| href="vipsmanualse15.html#x22-930003.3.1">3.3.1<!--tex4ht:ref: sec:wrapone --></a>. |
| |
| |
| |
| |
| <!--l. 1--><div class="crosslinks"><p class="noindent">[<a |
| href="vipsmanualse14.html" >next</a>] [<a |
| href="vipsmanualse13.html" >front</a>] [<a |
| href="vipsmanualch3.html#vipsmanualse13.html" >up</a>] </p></div> |
| <!--l. 1--><p class="indent" > <a |
| id="tailvipsmanualse13.html"></a> |
| </body></html> |
