Computer Graphics with Photoshop - changing background color in transparency

Author

changing background color in transparency

2004-09-03, 8:50 pm

Hello,

I feel silly for asking this, as I know I've learned this before,
but I've forgotten how to do this. I need to move a gif with
transparent background (assuming a white background, the color
graduates to white along the edges) to a background color other than
white. How do I get it to avoid looking crappy with the whiteness
showing up after the move to the new color?

Thanks for helping me out.

Paul

Mike Russell

2004-09-03, 8:50 pm

PM wrote:
> Hello,
>
> I feel silly for asking this, as I know I've learned this before,
> but I've forgotten how to do this. I need to move a gif with
> transparent background (assuming a white background, the color
> graduates to white along the edges) to a background color other than
> white. How do I get it to avoid looking crappy with the whiteness
> showing up after the move to the new color?

This is not directly possible, unfortunately, because GIF supports an all or
nothing transparency. This is one of the reasons you seldom see drop
shadows for a gif image. Here are some common workarounds:

1) make your gif with pixel accurate edges, instead of relying on a matte
color. You may see jaggies with this method, but at least there will be no
white edges.

2) us a large number of gif images, with different edge color combinations,
and change the gif according to the location on the page.

3) If the image has inherrently soft edges, e.g. a cloud, dither the edges
of your image instead of fading it to the matte color.

4) use a png image instead of gif. Png supports a true alpha channel. The
drawback is that some browsers ain't got a thing cuz they don't got that
PNG.

None of these is a perfect solution - but at least now you know why web
animations against a gradient background are so rare.
--

Mike Russell
www.curvemeister.com
www.geigy.2y.net

iehsmith

2004-09-06, 12:14 pm

On 9/3/04 8:15 PM, Hecate uttered:

> On 3 Sep 2004 13:29:01 -0700, pm@pmbooks.com (PM) wrote:
>
> Resave the original image with a different matte.
>
> --
>
> Hecate - The Real One
> Hecate@newsguy.com
> veni, vidi, reliqui
>

I'm thinking that Paul doesn't have the original. Paul, can you upload the
GIF in questions somewhere we can see it? The answer could be simple or
complex, depending on the image.

inez