galfar.imaginglib/Doc/VampyreDoc/FileFormats/Jpeg.xml

<?xml version="1.0" encoding="utf-8"?>
<?xml-stylesheet type="text/xsl" href="../Xsl/doc2html.xsl"?>
<doc>
  <title>JPEG File Format</title>
  <chapter>
    <title>JPEG File Format</title>
    <par>
      JPEG (Joint Photographic Experts Group) format
      is good choice for storing images with large number of colors
      and without sharp edges. It uses lossy compression which can greatly
      reduce size of image file. Imaging uses Independent JPEG Group's <b>jpeglib</b>
      library to load and save JPEG files. It was translated to Pascal by
      Jacques Nomssi Nzali. As stated in jpeglib's documentation this library
      can read and write <b>JFIF</b> format which is most widely used JPEG
      format. But there are also some proprietary and other JPEG formats
      which can not be read/written by jpeglib thus Imaging can not
      read/write them also.
    </par>

    <table>
      <title>JPEG File Format Support</title>
      <row>
        <th>Format</th>
        <th>TImageFormat equivalent</th>
        <th>Loading</th>
        <th>Saving</th>
      </row>
      <row>
        <td>24 bit RGB</td>
        <td><icode>ifR8G8B8</icode></td>
        <td>Yes</td>
        <td>Yes</td>
      </row>
      <row>
        <td>8 bit grayscale</td>
        <td><icode>ifGray8</icode></td>
        <td>Yes</td>
        <td>Yes</td>
      </row>
    </table>

    <par>
      When working with JPEG files you can find useful some options
      which can be set by <ref>SetOption</ref> function and their current values
      can be get by <ref>GetOption</ref> function.
      Or you can set them by modifying properties of <ref>TJpegFileFormat</ref>
      class.
    </par>
    
    <table>
      <title>Options Related to JPEG Files</title>
      <row>
        <th>OptionId</th>
        <th>Allowed Values</th>
        <th>Usage</th>
      </row>
      <row>
        <td><ref>ImagingJpegQuality</ref></td>
        <td><b>1</b> to <b>100</b></td>
        <td>JPEG compression quality used when saving images.
        Higher value means worse compression/better image quality/larger file size.
        Default value is <b>90</b>.</td>
      </row>
      <row>
        <td><ref>ImagingJpegProgressive</ref></td>
        <td><b>0 (False)</b> or <b>1 (True)</b></td>
        <td>Indicates whether JPEG is saved as progressive or not.
        Progressive JPEG rearranges the stored data into a series of scans of
        increasing quality.  In situations where a JPEG file is transmitted across a
        slow communications link, a decoder can generate a low-quality image very
        quickly from the first scan, then gradually improve the displayed quality as
        more scans are received. Default value is <b>0 (False)</b>. </td>
      </row>
    </table>

  </chapter>
</doc>