fc4b217c4a
help system Piers Cornwell <piers.cornwell@bigfoot.com> who has taken the burden to continue this project Karin and Olof started. --Sven
117 lines
4.7 KiB
HTML
117 lines
4.7 KiB
HTML
<!doctype html public "-//w3c//dtd html 4.0 transitional//en">
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<HTML>
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<HEAD>
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<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
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<TITLE>Indexed Mode</TITLE>
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</HEAD>
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<BODY text="#000000" bgcolor="#FFFFFF" link="#0000FF" vlink="#FF0000" alink="#000088">
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<TABLE width="100%" cellspacing="1" cellpadding="1">
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<TR bgcolor="black">
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<TD width="100%" align="center"><FONT size="+2" color="white">Indexed
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Mode</FONT></TD>
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</TR>
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<TR bgcolor="white" >
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<TD width="100%" align="left"><P>
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<P>
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This mode enables you to convert your RGB or Grayscale Image to an Indexed
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image. An Indexed image is a image which only can have the colors specified
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in it's color palette present in the image file. The maximum number of colors
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in a Index image is 256. If you want to make e.g transparent GIF images then
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you can only have a maximum of 255 colors since the last color (i.e color
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number 256) will be used to determine if the pixel is opaque or transparent.
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<H4>
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Palette Options
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</H4>
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<DL>
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<DD>
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<DT>
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<EM>Generate optimal palette:</EM>
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<DD>
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This is most of the time the best options to create a indexed image with.
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Gimp will evaluate your colors and create a color palette suitable for the
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image. You can specify the amount of colors that you want to have in your
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index image but remember that you can't have more than 255 colors if are
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about to create a index image with transparency.
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<DT>
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<EM>Use custom palette:</EM>
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<DD>
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If you want to use a predefined palette you have to use this option. You
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have to choose your palette from the drop down menu, by default it's Web
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palette. The Web palette is the palette used by e.g Netscape. This will help
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you create web safe index images images (There is some debate if you should
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index against the Web palette or not).
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<DL>
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<DT>
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<EM>Custom Palette Options:</EM>
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<DD>
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Remove unused colors from final palette: If the palette contains colors that
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aren't used in the Index image you can remove those colors and make the image
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file size smaller. This is a good option so keep it enabled.
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</DL>
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<DT>
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<EM>Use black/white (1-bit) palette:</EM>
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<DD>
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This option will create a "monochrome" image only built up of either black
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or white pixels.
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</DL>
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<H4>
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Dithering
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</H4>
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<P>
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An Index image can only be built up of a maximum of 256 colors. Most of the
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time this is quite limited and you will not be able to have all the colors
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in your image represented in this limited color space. The image will look
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like it is built up of "bands" or "color areas". To make Index images look
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better you can dither them. This means that you will mix two or several colors
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to mimic the missing color. The disadvantage is that the image can look like
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it's built up of "dots".
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<P>
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<DL>
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<DT>
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<EM>No color dithering:</EM>
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<DD>
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Will disable dithering totally.
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<DT>
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<EM>Positioned color dithering:</EM>
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<DD>
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This is a option to use when you are dealing with animations (e.g gif
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animations). The problem with dithering with e.g Floyd Steinberg dithering
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in animations is that the dithering will not be constant. If you instead
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use positioned dithering the dithering in constant areas will remain constant
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across your frames. It is not as good as Floyd Steinberg dithering but is
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better than no dithering at all.
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<DT>
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<EM>Floyd Steinberg dithering color dithering (reduced color
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bleeding):</EM>
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<DD>
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When you use normal Floyd Steinberg dithering you will experience that the
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colors will bleed to much . This is very visible when you index gradients,
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the effect is that the gradient will look unnatural. If you encounter this
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effect it's advisable to use this option (i.e Floyd Steinberg dithering reduced
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colour bleeding).
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<DT>
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<EM>Floyd Steinberg dithering (normal):</EM>
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<DD>
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This is the best option to use when you are indexing images. It's only in
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special cases that you will use the other dithering methods available.
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<DT>
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<DD>
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<DT>
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<EM>Enable dithering of transparency:</EM>
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<DD>
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Indexed images only have one transparency mode either it is off (the pixel
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is totally solid) or on (the pixel is totally transparent). This makes it
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very difficult to index images with smooth transitions from opaque to
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transparent. When you enable dithering of transparency Gimp will try to mimic
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the smooth transition by dithering pixels on and off. Note: A good alternative
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to transparency dithering is the
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<CODE><A HREF="../filters/semiflatten.html">Right-Click|Filters|Colors|Semi-Flatten</A></CODE>
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function.
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</DL>
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<P>
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<A href="index.html">Index</A>
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</TD>
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</TR>
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</TABLE>
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</BODY></HTML>
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