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<TITLE>Compressing a JPEG File (Java Developers Almanac Example)
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<h1>The Java Developers Almanac 1.4</h1>
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<B><A HREF="../javax.imageio/pkg.html">javax.imageio</A></B><font color="#666666" class="xsmall-font">
[6 examples]
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<h3>e699. Compressing a JPEG File</h3>
This example implements a method for writing a JPEG file with a
specific compression quality. In J2SE 1.4, the compression capability
is not functioning properly. This example demonstrates a workaround.
<pre> // Reads the jpeg image in infile, compresses the image,
// and writes it back out to outfile.
// compressionQuality ranges between 0 and 1,
// 0-lowest, 1-highest.
public void compressJpegFile(File infile, File outfile, float compressionQuality) {
try {
// Retrieve jpg image to be compressed
RenderedImage rendImage = ImageIO.read(infile);
// Find a jpeg writer
ImageWriter writer = null;
Iterator iter = ImageIO.getImageWritersByFormatName("jpg");
if (iter.hasNext()) {
writer = (ImageWriter)iter.next();
}
// Prepare output file
ImageOutputStream ios = ImageIO.createImageOutputStream(outfile);
writer.setOutput(ios);
// Set the compression quality
ImageWriteParam iwparam = new MyImageWriteParam();
iwparam.setCompressionMode(ImageWriteParam.MODE_EXPLICIT) ;
iwparam.setCompressionQuality(compressionQuality);
// Write the image
writer.write(null, new IIOImage(rendImage, null, null), iwparam);
// Cleanup
ios.flush();
writer.dispose();
ios.close();
} catch (IOException e) {
}
}
// This class overrides the setCompressionQuality() method to workaround
// a problem in compressing JPEG images using the javax.imageio package.
public class MyImageWriteParam extends JPEGImageWriteParam {
public MyImageWriteParam() {
super(Locale.getDefault());
}
// This method accepts quality levels between 0 (lowest) and 1 (highest) and simply converts
// it to a range between 0 and 256; this is not a correct conversion algorithm.
// However, a proper alternative is a lot more complicated.
// This should do until the bug is fixed.
public void setCompressionQuality(float quality) {
if (quality < 0.0F || quality > 1.0F) {
throw new IllegalArgumentException("Quality out-of-bounds!");
}
this.compressionQuality = 256 - (quality * 256);
}
}
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<b>Related Examples</b></font></td>
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e694. <a class="eglink" href="BasicImageRead.html?l=rel">
Reading an Image from a File, InputStream, or URL
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e695. <a class="eglink" href="Graphic2File.html?l=rel">
Saving a Generated Graphic to a PNG or JPEG File
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e696. <a class="eglink" href="GetFormats.html?l=rel">
Listing the Image Formats That Can Be Read and Written
</a>
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e697. <a class="eglink" href="DetermineFormat.html?l=rel">
Determining If an Image Format Can Be Read or Written
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e698. <a class="eglink" href="DiscType.html?l=rel">
Determining the Format of an Image in a File
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