Demonstration of various methods of encoding the main image (PNG and JNG) and the alpha channel (IDAT, JDAA, 16-color IDAT, and low-quality JDAT)
If you are looking at this with Netscape 4.x, you won't see the transparency. Download the images and look at them with an alpha-capable viewer like rpng-x that comes with libpng. ImageMagick will reduce the alpha to binary transparency with a threshold of 1, so you will just see oval images without the gradient. Screen shots are shown to the right. The JPEG "q" numbers are ImageMagick "quality" values. Except for the second row which is an actual JNG, the other JNGs have been converted back to JPEG or PNG so you can see them. File sizes (except for the RGBA PNG) are the JNG file sizes.
For another demo with JNG and MNG files, see http://pmt.sourceforge.net/jdaa/demo2.html
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| RGBA PNG, 205812 bytes | |
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| Actual JNG, main q65, alpha q30, 10364 bytes | |
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| JNG as PNG, main q65, alpha q30, 10364 bytes | |
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| JNG as PNG, main q65, alpha 16-color PNG, 13376 bytes | |
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| JNG as PNG, main q65, alpha q5, 8966 bytes | |