exporting gif files ... help please ? :)

[judyjudy]

I need to understand the difference in exporting gifs using web pallete vs optimized pallete.

When I use web pallete the image is distorted (heavily pixelized) when viewed at lower resolutions on larger screen monitors. So, I want to get a better understanding of the optimized pallete to decide if I should use it.

Also, when using the optimized pallete, there are 3 choices available for the number of bits: 8, 4, and 1. However, you can limit the number of colors regardless of which bit size you use, and that effects a file size. I would like that explained as well.

I think what I may need are some technical documents on how Xara exports gifs.

Thanks in advance for any info that you may be able to pass on to me.

JudyG

[judyjudy]

I need to understand the difference in exporting gifs using web pallete vs optimized pallete.

When I use web pallete the image is distorted (heavily pixelized) when viewed at lower resolutions on larger screen monitors. So, I want to get a better understanding of the optimized pallete to decide if I should use it.

Also, when using the optimized pallete, there are 3 choices available for the number of bits: 8, 4, and 1. However, you can limit the number of colors regardless of which bit size you use, and that effects a file size. I would like that explained as well.

I think what I may need are some technical documents on how Xara exports gifs.

Thanks in advance for any info that you may be able to pass on to me.

JudyG

[Sean Sedwards]

Judy

My best advice is to study the Xara help file, which is very comprehensive. Of particular relevance is the "Internet Bitmaps Overview" page.

Briefly, the fewer the colours, the smaller the file size and the lower the quality. The bit size of the palette defines the maximum number of colours available for that sub-format (GIF has a maximum of 8-bit = 256), however you can edit the number to further reduce the file size. PCs work in 24-bit colour (16.8 million colours), so Xara has to pick 256 (or fewer) to best represent your image.

The web palette is a fixed range of 216 colours covering the entire spectrum. Using this more or less guarantees how the image will look on all machines at the expense of quality. Because the palette is fixed, your image may only use a fraction of the available colours and to simulate the colours not in the palette, Xara may use dithering, which is like putting a black pixel next to a white pixel to give the impression of grey. Dithering usually makes the image appear more pixelated because it uses more than one pixel per ideal pixel.

An optimised palette gives the best quality because it uses your image as a basis for its choice of colours. Dithering is far less obtrusive but is usually unnecessary and will likely increase the file size. The drawback with an optimised palette is that the GIF may not look its best when displayed on a computer that can only display 256 colours, however those are becoming increasingly rare.

Regards - Sean

[This message was edited by Sean Sedwards on October 16, 2000 at 02:39 AM.]