Question : Gimp and the indexed and RGB image modes...

What are these image modes in Gimp? Why on an indexed gif image, I chosen color appears differently on the image? And why the font Helvetica Adobe is different on the indexed gif and on the RGB gif?
Stephane

Answer : Gimp and the indexed and RGB image modes...

Stephane,

I wrote you a nice, long answer but got cut off by EE and lost it all!  So here it goes again:

RGB color mode:  designed for on-screen viewing.  16.7 million colors in its gamut.  You can edit in all sorts of ways when working in this mode.

Indexed color mode:  uses a specified color palette of no more than 256 colors to (1) reduce file size and (2) better ensure what-you-see-is-what-you-get with output devices that can't do millions of colors.  You should have an option when you change from RGB to Indexed to use a Web palette - this consists of the 216 colors that all browsers will display on both PC and Mac.  You also can't do some types of editing in indexed mode (ie some filter effects).  You may want to save an RGB version before converting just in case you later want to go back and do some of these effects.

When you convert from RGB to indexed mode, colors outside of the indexed palette will be either replaced by a close match within the palette or approximated by mixing pixels of colors that are in the palette (the latter is called "dithering").  This is why your colors look different in indexed color mode.

GIF is always indexed.  If you need a larger color palette for a particular web image than you can get in the indexed mode, a JPG or a 24-bit PNG in RGB mode should suit your needs.

Changing color mode should not have any effect on the shape of characters from a font - if this is happening, it's extremely unusual.