Mercurial > hg > digilib-old

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<TITLE>Scaler servlet</TITLE>
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<H1>Scaler</H1>

<p>A Servlet for scaling images. (Version 1.16b2)</p>

<h2>Web API</h2>

<p>The Scaler servlet takes parameters in the http request format:
<code>Scaler/request_path/?param1=value1&param2=value2&...</code>
Unknown parameters will be silently ignored.</p>

<p>Recognised parameters:
<ul>
  <li><b>request_path</b> path to file or directory.</li>

  <li><b>fn</b> path to file or directory below <code>/docuserver/images</code>
    (or other configured image directory).
    This path will be added to the <code>request_path</code> behind the servlet name.
    Either parameter can be empty.</li>

  <li><b>pn</b> page number. Index into the (alphabetically sorted) directory
    given by the path. Starts with 1. Ignored if the path points to a file.
    Default: 1.</li>

  <li><b>dw</b> destination image width (pixels). If omitted the image is scaled to fit
    dh.</li>

  <li><b>dh</b> destination image height (pixels). If omitted the image is scaled to fit
    dw.</li>

  <li><b>wx</b> relative x offset of the image area to be sent (0 &lt;= wx &lt;= 1).
    Default: 0.</li>

  <li><b>wy</b> relative y offset of the image area to be sent (0 &lt;= wy &lt;= 1).
    Default: 0.</li>

  <li><b>ww</b> relative width of the image area to be sent (0 &lt;= ww &lt;= 1).
    Default: 1.</li>

  <li><b>wh</b> relative height of the image area to be sent (0 &lt;= wh &lt;= 1).
    Default: 1.</li>

  <li><b>ws</b> additional scaling factor. The resulting image will have the size
    <code>[ws*dw,ws*dh]</code>. Default: 1.</li>

    <li><b>mo</b> flags for the mode of operation separated by ",".
    <ul>
      <li><b>fit</b>: always scale the image to fit
      <code>[dw,dh]</code>.<br>

      <b>file</b>: send the file as-is (may
      be very large and all sorts of image types!). If configuration
      doesn't allow sending files
      (<code>sendfile-allowed=false</code>) revert to
      <code>clip</code>.<br>

      <b>rawfile</b>: send the file as-is with a mime-type of
      <code>application/octet-stream</code> so it can be downloaded with
      the browser.<br>

      <b>clip</b>: send the file in its
      original resolution, cropped to fit <code>[dw,dh]</code>.<br> If
      none of these flags is set heuristics is used (send unzoomed GIF
      as-is).<br>

      <b>osize</b>: scale to original size based on the image resolution
      (from the image metadata) and display resolution (from parameter
      <code>ddpi</code>). Fails if either resolution is unknown.
      </li>

      <li><b>errtxt</b>: send error response as HTML.<br>
      <b>errimg</b>: response as image (default).</li>

      <li><b>q0</b>-<b>q2</b>: quality of interpolation in scaling
      (<code>q0</code>: worst, default).</li>

      <li><b>lores</b>: try to use scaled image (default)<br>

      <b>hires</b>: always use unscaled image.<br>

      If the image is zoomed (ww, wh &lt; 1) the unscaled image is
      used in any case.</li>

      <li><b>vmir</b>: mirror image vertically.<br>

      <b>hmir</b>: mirror image horizontally.</li>
    </ul>
  </li>

  <li><b>cont</b>: change contrast of the image. Negative value
  reduces contrast, positive value enhances contrast. Pixel value is
  multiplied by 2^cont. Default: 0</li>

  <li><b>brgt</b>: change brightness of image. Negative value reduces
  brightness, positive value enhances brightness. The value brgt is
  added to the pixel value. Default: 0</li>

  <li><b>rot</b>: rotate image. Rotation angle is given in
  degrees. Default: 0</li>

  <li><b>rgbm</b>: modify color by multiplication. The contrast of the
  red green and blue components of the image can be reduced or
  enhanced similar to the <code>cont</code> parameter. The factors for
  red, green and blue are separated by slashes (for example
  0.86/0/-0.5). Default: 0/0/0</li>

  <li><b>rgba</b>: modify color by addition. The brightness of the red
  green and blue components of the image can be reduced or enhanced
  similar to the <code>brgt</code> parameter. The factors for red,
  green and blue are separated by slashes (for example
  100/0/25). Default: 0/0/0</li>

  <li><b>ddpi</b>: resolution of client display for <code>osize</code> mode.
  Either <code>ddpi</code> or <code>ddpix</code> and <code>ddpiy</code> must
  be set to use <code>osize</code> mode.</li>

  <li><b>ddpix</b>: resolution of client display in x direction for
  <code>osize</code> mode.</li>

  <li><b>ddpiy</b>: resolution of client display in y direction for
  <code>osize</code> mode.</li>

</ul>
The image will be scaled equally in horizontal and vertical direction such that
the resulting image does not exceed the rectangle <code>[ww,wh]</code>.
</p>

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author	robcast
date	Fri, 21 Nov 2003 00:30:04 +0100
parents	3258490649b5
children	250f3b8762e4