does .gif support alpha channel

[Master chief]

just wondering if any one knows but i need to know if a . gif format will support having a alpha channel , when i get home i want to try and make an animated gif that has transperant background parts and though i should ask first so i don't get my hopes up

[NancyGormezano]

just wondering if any one knows but i need to know if a . gif format will support having a alpha channel , when i get home i want to try and make an animated gif that has transperant background parts and though i should ask first so i don't get my hopes up

 

gif format does support a key or "alpha" channel

[Rodney]

As Nancy suggests the Gif format does support transparency.

Programs that allow it will let you choose a single color to designate as transparent.

Often this'll be a color not used in the image such as bright pink.

When the image is displayed the view then keys the pink as transparent.

 

I suppose it could be said that Gif images support one alpha channel but I think that is a stretch of the definition.

 

Images that support an alpha channel have a grayscale layer (the alpha channel) that specifies how transparent any part of the image (each pixel) will be regardless of the color. Gif images are still RGB images whereas Targas, PNG and other formats that support alpha channels are RGBA. (Red Green Blue and Alpha channels)

 

Of interest to A:M users, the Alpha Channel was invented by Ed Catmull and Alvy Ray Smith.

Ed Catmull of course being of Pixar fame and the guy who Martin Hash studied with.

 

(I'd be more accurate with some of this wording but my daughter is kicking me off the computer. Julia says 'Hi' and 'Bye')

 

Edit: Here is the wikipedia write up on alpha channels.

[NancyGormezano]

ah yes, thanks for being more accurate, Rodney

[robcat2075]

I recall A:M had a render option to NOT anti-alias the edges of an object. This was intended for game programmers making sprites in pre-alpha channel days, but could be useful to make halo-less GIFs with transparency.

 

Don't ask me where to find that option or if it still exists.

[Rodney]

Don't ask me where to find that option or if it still exists.

 

I may be completely off base here so take this as a guess.

 

As far as I know this is now accomplished by Multipass.

Once Multipass is set for 4 passes above the Soften option will appears. You can change the percentage there.

As long as the image is high enough resolution you should get the desired effect of aliasing (or anti-aliasing) via multipass.

Turning the Alpha Channel on (with image formats that support alpha channels) should take care of the rest.

 

guess>

 

 

Edit: Looks like that was a lucky guess. Here is a very old quote from Jeffrey Dates (emphasis added in bold):

 

A:M NetRender has a multipass feature that renders the same frame multiple times. This slows rendertimes greatly, but increases render quality beyond words. It improves all anomolies of motion blur... it is no longer nescessary to antialias... Dmap shadows are WAY more realistic in the latest beta due to some new jitter effects added to the lights.

 

The trick is finding the number of passes that looks the best and isn't an overkill. At somepoint there won't be an apparent difference in quality between the number of passes.. (but a HUGE speed hit).

 

What the multipass does is:

 

Say you have frame 1 and 2.. and multipass set to 16 passes. A:M divides the "time" between 1 and 2 into 16 segments. It then renders each segment and overlays the results.

 

So motion blur is rendered 16 times each one slightly offset. (which gives a more realistic look).

 

There is no need to antialias because it is redrawing the scene 16 times.. so in that process the edges are redrawn 16 indivdual times and overlayed.

We use multi-pass exclusivly for all our renders and it gives us amazing photoreal results. (You should see some of the HDTV stuff we rendered at 25 passes!)

 

Jeffrey Dates

 

 

This of course was from before A:M had Netrender's Multipass feature included.

If you've got the current version, you've got Multipass.

[Rodney]

To bring this discussion back around to .GIFs.

A lot will depend on the program you use to convert your images or image sequences to GIF in.

There are many programs that will do this. AVI2GIF comes to mind.

But not all of them support transparency.

For this you'll have to experiment.

 

When worse comes to worse and you are in a pinch you can make the background the same color as your webpage and then link the GIF animation in. If you don't need the transparency that'll help a bit.

 

Animated GIFs are just a little more complicated than still GIF as you must specify the color that will be transparent in the image. The more capable programs (those that cost money) should convert your Alpha Channel automatically.

 

I have a feeling masking your animation with a specific color background may be your best bet.

Then you can select that color in the program you use to convert to animated GIF.

If you want to go that route I'd recommend a freeware program like AVI2GIF.

With that you can render out of A:M to AVI and then convert to GIF.

No transparency... but quick.

[robcat2075]

Don't ask me where to find that option or if it still exists.

 

I may be completely off base here so take this as a guess.

 

As far as I know this is now accomplished by Multipass.

 

This is not the same thing. The option I referenced is intended to NOT anti-alias edges. It's not about creating a result that does the same thing as anti-aliasing. It is intended to leave them jaggy so that there is none of the halo-producing transparency that you would normally get when you use a single color key as a basis for transparency in a GIF..

 

I found it. It is accomplished now with the "Alias Edges" post effect.

[Rodney]

I found it. It is accomplished now with the "Alias Edges" post effect.

 

Ah. Very different things. Thanks for the clarification Robert.

Note to self: Experiment with the Alias Edges post effect.