Name: rmT116609 Date: 02/05/2004


FULL PRODUCT VERSION :
java version "1.4.1_01"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.1_01-b01)
Java HotSpot(TM) Client VM (build 1.4.1_01-b01, mixed mode)
java version "1.4.2"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.2-b28)
Java HotSpot(TM) Client VM (build 1.4.2-b28, mixed mode)



FULL OPERATING SYSTEM VERSION :
glibc-2.2.2
Linux 2.4.19 i686
Slackware-based

A DESCRIPTION OF THE PROBLEM :
The size of the PNG images created by PNGImageWriter is
considerably
larger than created by other PNG creation tools such as gif2png,
Netpbm, etc., for the same image contents.

By inspecting PNG images generated by PNGImageWriter, following
problems were found. For indexed color images (color type 3),
adaptive filter (filter type 1-4) is applied to the scanlines.
So the randomness of the filtered data increases, and
the compression ratio is dropped. According to the
PNG Specification (http://www.libpng.org/pub/png/spec/),
filter type 0 is recommended for the indexed color images.

Conversely, for true color images (color type 2) generated by
PNGImageWriter, filter type 0 is only applied. PNG Spec
recommends
to apply adaptive filter to true color images.

This problem is because, the logic to test if input image is
indexed-colored or not is backward, in the implementation of
com.sun.imageio.plugins.png.RowFilter#filterRow(int,byte[],byte[],byte[][],int,int).

Currently:
        // Use type 0 for palette images
        if (colorType != PNGImageReader.PNG_COLOR_PALETTE) {
Should:
        // Use type 0 for palette images
        if (colorType == PNGImageReader.PNG_COLOR_PALETTE) {


REPRODUCIBILITY :
This bug can be reproduced always.
(Incident Review ID: 181605)
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