jdk/src/share/classes/javax/imageio/package.html

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The main package of the Java Image I/O API.

<p>

Many common image I/O operations may be performed using the static
methods of the <code>ImageIO</code> class.

<p>

This package contains the basic classes and interfaces for describing
the contents of image files, including metadata and thumbnails
(<code>IIOImage</code>); for controlling the image reading process
(<code>ImageReader</code>, <code>ImageReadParam</code>, and
<code>ImageTypeSpecifier</code>) and image writing process
(<code>ImageWriter</code> and <code>ImageWriteParam</code>); for
performing transcoding between formats (<code>ImageTranscoder</code>),
and for reporting errors (<code>IIOException</code>).

<p>
All implementations of javax.imageio provide the following standard
image format plug-ins:
</p>
<div>
<table border=1 align='center' cellpadding=5>
<tr>
    <th>&nbsp;</th> <th>Reading</th> <th>Writing</th>
    <th>Notes</th> <th>Metadata</th>
</tr>
<!-- JPEG plugin -->
<tr>
    <td> <a href="http://www.jpeg.org">JPEG</a></td>
    <td align='center'>yes</td>
    <td align='center'>yes</td>
    <td align='center'>none</td>
    <td align='center'><a href='metadata/doc-files/jpeg_metadata.html'>
    JPEG metadata format</a></td>
</tr>
<!-- PNG plugin -->
<tr>
    <td><a href="http://www.libpng.org/pub/png/spec/">PNG</a></td>
    <td align='center'>yes</td>
    <td align='center'>yes</td>
    <td align='center'>none</td>
    <td align='center'><a href='metadata/doc-files/png_metadata.html'>
    PNG metadata format</a></td>
</tr>
<!-- BMP plugin -->
<tr>
    <td>BMP</td>
    <td align='center'>yes</td>
    <td align='center'>yes</td>
    <td align='center'>none</td>
    <td align='center'><a href='metadata/doc-files/bmp_metadata.html'>
    BMP metadata format</a></td>
</tr>
<!-- WBMP plugin -->
<tr>
    <td><a href="http://www.wapforum.org/what/technical/SPEC-WAESpec-19990524.pdf">WBMP</a></td>
    <td align='center'>yes</td>
    <td align='center'>yes</td>
    <td align='center'>none</td>
    <td align='center'><a href='metadata/doc-files/wbmp_metadata.html'>
    WBMP metadata format</a></td>
</tr>
<!-- GIF plugin -->
<tr>
    <td><a href="http://www.w3.org/Graphics/GIF/spec-gif89a.txt">GIF</a></td>
    <td align='center'>yes</td>
    <td align='center'>yes</td>
    <td align='center'><a href="#gif_plugin_notes">
    GIF plug-in notes</a></td>
    <td align='center'><a href='metadata/doc-files/gif_metadata.html'>
    GIF metadata format</a></td>
</tr>
</table>
</div>
<BR>
<BR>
<BR>

<h2> Standard Plug-in Notes</h2>
<h3><a name="gif_plugin_notes">Standard plug-in for GIF image format</a></h3>


<p>
ImageIO provides <code>ImageReader</code> and <code>ImageWriter</code>
plug-ins for the <a href="http://www.w3.org/Graphics/GIF/spec-gif89a.txt">
Graphics Interchange Format (GIF)</a> image format.

These are the "standard" GIF plug-ins, meaning those that are included in the
JRE, as distinct from those included in standard extensions, or 3rd party
plug-ins. The following notes and metadata specification apply to the
standard plug-ins.

<h3>Writing GIF images</h3>
 The GIF image writer plug-in guarantees lossless writing for images which meet
 the following requirements:
<ul>
<li>the number of bands is 1;
<li>the number of bits per sample is not greater than 8;
<li>the size of a color component is not greater than 8;
</ul> </p>
 
<p>
 By default the GIF writer plug-in creates version "89a" images. This can be
 changed to "87a" by explicitly setting the version in the
 stream metadata (see <a
 href="metadata/doc-files/gif_metadata.html#gif_stream_metadata_format">
 GIF Stream Metadata Format Specification</a>).
</p> 
 
 
<!-- animated images -->
<p>
 The GIF writer plug-in supports the creation of animated GIF images through
 the standard sequence writing methods defined in the
 <code>ImageWriter</code> class.
 
 <!-- TODO: add example here --> 
</p>
 
<!--  color tables -->
<p>
 A global color table is written to the output stream if one of the
 following conditions is met:
 <ul>
 <li> stream metadata containing a GlobalColorTable element is
  supplied; </li>
 <li> a sequence is being written and image metadata containing a
  LocalColorTable element is supplied for the first image in the
  sequence;</li>
 <li>image metadata is not supplied or does not contain a LocalColorTable
  element. </li>
 </ul>
 
 <p>
 In the first case the global color table in the stream metadata is
  used, in the second the local color table in the image metadata is
  used, and in the third a global color table is created from the
  ColorModel or SampleModel of the (first) image.
 </p>
 
 <p>
 A local color table is written to the output stream only if image
  metadata containing a LocalColorTable element is supplied to the
  writer, or no image metadata is supplied to the writer and the local
  color table which would be generated from the image itself is not
  equal to the global color table.
 </p>
 
 <p>
 A Graphic Control Extension block is written to the output stream only
  if image metadata containing a GraphicControlExtension element is
  supplied to the writer, or no image metadata is supplied and the
  local color table generated from the image requires a transparent
  index. Application, Plain Text, and Comment Extension blocks are
  written only if they are supplied to the writer via image metadata. 
 
 </p>
 
 <!-- writing interlaced images -->
 <p>
 
  The writing of interlaced images can be controlled by the progressive
  mode of the provided <code>ImageWriteParam</code> instance.
  If progressive mode is
  <code>MODE_DISABLED</code> then a non-interlaced image will be written. If
  progressive mode is <code>MODE_DEFAULT</code> then an interlaced image will
  be written. If progressive mode is <code>MODE_COPY_FROM_METADATA</code>, then
  the metadata setting is used (if it is provided, otherwise an interlaced
  image will be written).
 </p>
 
 <p>
 The GIF image writer plug-in supports setting output stream metadata from
 metadata supplied to the writer in either the native GIF stream
 metadata format <a href="metadata/doc-files/gif_metadata.html#gif_stream_metadata_format">
 javax_imageio_gif_stream_1.0 </a> or the standard metadata format
 <a href="metadata/doc-files/standard_metadata.html">
 javax_imageio_1.0</a>, and setting
 output image metadata from metadata supplied to the writer in either
 the native GIF image metadata format <a href="metadata/doc-files/gif_metadata.html#gif_image_metadata_format">
 javax_imageio_gif_image_1.0 </a> or the standard metadata format
 <a href="metadata/doc-files/standard_metadata.html">javax_imageio_1.0</a>.
  
 The mapping of standard metadata format to the GIF native stream and
 image metadata formats is given in the tables <a
 href="metadata/doc-files/gif_metadata.html#mapping"> here </a>.
 </p>


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Java<SUP><FONT SIZE="-2">TM</FONT></SUP> Image I/O API Specification
<BR>
<BR>
Public Draft 2 (specification version 0.5)
<BR>
Release: October 1, 2000
<BR>
<BR>

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@since 1.4
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