Re: FLASH: Alpha Channels Messed up?

[John Dowdell]

At 6:21 AM 12/9/98, Adam Bruce wrote:

>I noticed two things yesterday, Aftershock doesn't perfectly match the

>HTML background to the movie background if you have a custom color. And

>Secondly, if you set the window mode to "transparent Windowless"  Alpha

>Channels fade to the color of the movie background instead of the HTML

>background causing a "ghosting" effect.


Not "messed up", just initial expectation diverging from reality, that's

all. Here's the background.


It can be difficult to give the illusion of things floating in browser

windows today. One great reason is because people can use different

browsers. Netscape or Microsoft/Mac browsers don't offer reliable

windowless abilities yet, for instance.


Even trying to match background colors is difficult, because you're relying

on each browser and each video system to interpret the colors from various

sources the same way. When some colors are rendered by the various browser

engines, and some colors are rendered by a multimedia player, then even a

very small difference in any of the RGB values will be perceptible.


(You're guaranteed color-rounding differences on at least some machines,

because "thousands of colors" have only 32 distinct values for red, green,

or blue, compared to the 256 distinct values of each available in

"millions" or "hundreds of colors" displays.)


And yes, the windowless ActiveX Control will support chromakey and

antialiasing, but not variable transparency, sorry... while we can apply

256-valued alpha *within* Flash, that's not available from control to host.


Summary: It can be difficult to universally match colors among different

devices. It may be better to design so that this is not a necessity.


jd




John Dowdell, Macromedia Tech Support, San Francisco CA US


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