create PNG images in palette mode in Java

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babz - 28 Oct 2005 05:22 GMT

Java does not allow us to use more than 16 entries in the color map of
the Index Color Model for palette mode PNG encoding.
This disrupts the quality of images drastically. Is there a way to
improve the image quality?

This is the code I used:

int cmap[] = {

        0x00000000,
    0xFF202020,
        0xFF0000FF,
        0xFF808080,
0xFF00FF00,
    0xFF00FFFF,
        0xFFFF0000,
    0xFFFF00FF,
    0xFFFFFF00,
    0xFFFFFFFF,
};

IndexColorModel colorModel = new IndexColorModel(8,
    cmap.length, cmap, 0, true, -1,
DataBuffer.TYPE_BYTE);

bufImg = new BufferedImage(width, height,
BufferedImage.TYPE_BYTE_INDEXED, colorModel);

Thanks,

Babz

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Roedy Green - 28 Oct 2005 07:13 GMT

>Java does not allow us to use more than 16 entries in the color map of
>the Index Color Model for palette mode PNG encoding.

Where did you learn that? Perhaps there is some related class without
the restriction. The limit seems odd given that most indexed
colourmaps in the Windows universe are 8-bit.

I display 17..255-colour map gifs and pngs all the time in Java,
though I could not be certain all the colours are being rendered
properly.

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Canadian Mind Products, Roedy Green.
http://mindprod.com Java custom programming, consulting and coaching.

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babz - 28 Oct 2005 10:06 GMT

so what do i do then? Can you think of a way that could prevent color
loss?

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Roedy Green - 28 Oct 2005 10:26 GMT

>so what do i do then? Can you think of a way that could prevent color
>loss?

I don't know. I have not used those classes. My suggestion was to look
around for some alternate class that support 8 bit palettes. Perhaps
something in JAI. See http://mindprod.com/jgloss/jai.html

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Canadian Mind Products, Roedy Green.
http://mindprod.com Java custom programming, consulting and coaching.

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Thomas Fritsch - 28 Oct 2005 15:16 GMT

> Java does not allow us to use more than 16 entries in the color map of
> the Index Color Model for palette mode PNG encoding.

What did actually happen, when you converted a BufferedImage like below
with a large IndexColorModel (say with cmap having 100 entries) to PNG?
Did you get any error, or did the PNG have too few colors, or was it
otherwise of bad quality? I got good results when converting a JPEG
photo to PNG (with a 125-color palette).

The BufferedImage bufImg in your example below is still empty. Hence:
Exactly how do you fill the pixels into that BufferedImage? There are
probably many ways to do this.
How did you convert that BufferedImage to PNG? I assume you did it with
ImageIO.write(bufImg, "PNG", ...).

> This disrupts the quality of images drastically. Is there a way to
> improve the image quality?
[quoted text clipped - 18 lines]
> bufImg = new BufferedImage(width, height,
> BufferedImage.TYPE_BYTE_INDEXED, colorModel);

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babz - 08 Nov 2005 05:23 GMT

Thomas wrote:

>I got good results when converting a JPEG photo to PNG (with a 125-color palette)

can you plz give me the set of color map entries you used? Because now
using more than 16 entries does not give me the exception I was getting
before.

Thanks,

Babz

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babz - 09 Nov 2005 08:12 GMT

Thomas wrote:

>I got good results when converting a JPEG photo to PNG (with a 125-color palette)

can you plz give me the set of color map entries you used? Because now
using more than 16 entries does not give me the exception I was getting

before.

Thanks,

Babz

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create PNG images in palette mode in Java

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