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Thread: About Palette files

  1. #11
    Moderator Sam_Zen's Avatar
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    Default About greyscale palettes

    This is a special category, because in these files all three RGB-values are the same.
    Of course very relevant if one is dealing with a B/W photograph.

    But there are complications in the process.
    Starting from a 24 BPP image one can travel several roads to make it greyscale.
    1~ Choose direct 'Image/Convert to Greyscale'
    2~ Choose 'Decrease color depth' to 256 colors, with 'make grayscale image' enabled.
    3~ Choose 'Decrease color depth' to 256 colors, save, and then do 'Image/Convert to Greyscale'.
    4~ Import a greyscale palette directly into a 24 BPP image to make it 8 BPP.

    Saving each palette file of the result will probably be different.
    An example about 'odd' behaviour in this :
    I do a 'Image/Convert to Greyscale' and then save the PAL file, it appears to be the standard 0-255 value file.
    With the proper representation in greyscale tints.
    If I directly import that same PAL file in the original 24 BPP file, it shows a different result (nr3):
    Several elements in these processes can play a role in this. I checked this apart from optional dithering.
    Last edited by Sam_Zen; 02.01.2008 at 06:02 AM.
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    Default About greyscale palettes II

    Since a file with a straight, lineair increase of the values 0.0.0 to 255.255.255, it could have another curve along the way,
    I've tried to make some palfiles where the gamma-values are pepped up or turned down in the default picture setting.
    But the pal file stays based on the same lineair increase unfortunately, if saved.
    This is a pity. It would be quite convenient to be able to load variations of the lineair original, to emphasise gamma, brightness, etc., caught in some formula.
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    I've found an opensource app called Color Select. By Josiah Reynolds.
    It's meant to be a color picker, but it's more than that.
    First, it has very detailed information about the color in all kinds of codes.


    Second, it has a tool for opening, editing and saving a palette.
    Due to the dialogs I noticed different kinds of palette formats :
    *.PAL PSP type - *.PAL M$ type - *.ACT Photoshop type. Read and write, so the tool is a converter too.
    It also has four default system palettes on board as a preset :
    MacIntosh
    Web 125 for Unix
    Web 216
    Windows system
    So I retrieved these 4 files and packed them into Pals 3
    Last edited by Sam_Zen; 18.02.2008 at 03:12 AM. Reason: other formats
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    Moderator Laurent's Avatar
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    Hi Sam Zen,

    I tried again to work with your palettes and it didn't work, until I discovered an option in Options | Properties/Settings | Misc. 3 -> "Import palette: use nearest color". Since I unchecked that box, everything is working file. I don't know what this option is.

    Laurent

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    Nice. A valid warning in this topic.
    I unchecked that box as well, because I didn't trust it. I wanted a straight, exact import of the palette.
    And I wondered too : "nearest color" to what ?
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    Moderator Laurent's Avatar
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    Hi Sam Zen,

    Another similar program is La boîte à Couleurs. Interesting for the name of the colors (in french). A page in english exists, but I don't know if the program is translated too.

    Laurent

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    Nice ColorBox. It runs in English too.
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    While checking the fractal generator ManpWin by Paul de Leeuw,
    I noticed that it uses the .MAP format for palette files, but also a new one, the 'True Color Map'.
    It has the extension .COL, and contains an ascii-file with six decimal values. Wondering what these represent.
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    Note that for grayscale conversion RGB values are not simply converted to shades of gray, but each color component is multiplied with a factor. This is based on human eye perception and gives better results.
    There is a difference in quality between assigning a 256 grayshade pallete and properly converting to grayscale using these factors.

  10. #20
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    You're absolutely right. there is a mathematical difference.
    Nevertheless, the main issue here is just assigning some palette, not improving the quality as such.
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