Trouble converting 24 bit image to 8 bit image...

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  1. #1
    Unregistered User Yarin's Avatar
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    Exclamation Trouble converting 24 bit image to 8 bit image...

    I can read and write the bitmap files just fine, but say I have now a large array of dwords (the dib's pixels) and I need to figure out what 256 colors I can use out of how ever many the 24-bit image has.

    I made an algorithim that uses the colors that occure most often in the bitmap. But I quickly learned that it's not good enough.

    I would link to make my program capable of acceptable 24 to 8 bit coversion. Like Corel Photo-Paint can do. Does anyone know how to make an algorithim that can do this good? I have done alot of googling, but I can't find anything.

    Please help.
    Yarin.
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    Dr Dipshi++ mike_g's Avatar
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    If you want to convert the bmp without a pallette this is pretty easy. Basically each byte would then hold the complete rbg value. the high 2 bits would be red, middle three green and the last two bits blue.

    I'm not sure how coral paint make 8 bit bitmaps but if you are using a palette png format would be better.

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    It's no easy task.

    If I remember correctly, Adobe photoshop, has 3 separate algorithms, for choosing a pallette, not inclding the predefined pallettes.

    Really, you should get an image editor to do this properly for you.
    It is too clear and so it is hard to see.
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    Registered User Codeplug's Avatar
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    What you want to Google is "dither algorithm".

    gg

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    Algorithm Dissector iMalc's Avatar
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    This is an absolutely fantastic article on dithering and colour palette reduction:
    http://en.wikipedia.org/wiki/Dither

    I believe the thing you asked about however is colour quantization, for which I'll point you at the folowing equally fantastic link:
    http://en.wikipedia.org/wiki/Color_quantization

    I highly suggest reading both!
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  6. #6
    Malum in se abachler's Avatar
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    Pallette optimization is a quite interesting field. You need to choose between speed and quality, as the best algorithms usually take the longest time. Its also easier to optimize a high resolution image than a low resolution one.
    Until you can build a working general purpose reprogrammable computer out of basic components from radio shack, you are not fit to call yourself a programmer in my presence. This is cwhizard, signing off.

  7. #7
    Unregistered User Yarin's Avatar
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    Thanks for the replys, but I already found out what to do. I created my own version of the Octree Quantization method, and it works sweet! Almost as good as Corel PP in fact.
    A class that doesn't overload all operators just isn't finished yet. -- SmugCeePlusPlusWeenie
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