Forums | MacLife

Iritscen · 2009-03-19 1:30 pm

I figured I'd try a forum I know and love before I try to find a broader non-Mac graphics forum. I was reading about how GIFs can be made to refresh only part of themselves from frame to frame. I've made GIFs in the past (I use ImageReady) but I don't know if this gets done automatically when you compress (I somehow doubt it), and if not, how to take advantage of this. Is there a GIF-making app that someone knows can do this? I also have a GIF that I suspect might use this partial-scan feature but I don't know how to confirm it; hopefully there's an app can can analyze GIFs to tell me this sort of thing.

D'Eyncourt · 2009-03-19 4:01 pm

While there are other utilities, I recommend GraphicConverter (US$35 shareware) for all of your basic graphics needs such as creating animated GIFs.

When making my own animated GIFs it did seem to me that GraphicConverter automatically did the comparison and "partial refresh" of the image as part of the effort to minimize the size of the file. What is actually happening is that it is taking advantage of GIF transparency by filling the rest of the frame with (usually) white which when overlaid over the previous image is rendered transparent. Since the transparent part is one color that portion of the GIF (usually) can be compressed more efficiently.

With GraphicConverter you can step through an animated GIF and see the contents of each frame, which should aid you in analyzing animate GIFs.

Iritscen · 2009-03-19 4:24 pm

I actually do own GraphicConverter, although I never used it to make a GIF. I'll have to give it a try tonight. On the subject of the GIF that I thought used partial refresh, I had already stepped through it in GC, and it shows each frame in full. Since I didn't know what this meant (i.e., does GraphicConverter layer each partial frame over the previous onscreen as you advance through frames, or would it actually show the partial frame?), I couldn't learn anything from the exercise. If I only had a GIF that I knew used partial refresh, I could see how GC displays it. Or are you certain about that part?

Metacell · 2009-03-19 4:32 pm

Gimp can optimize a series of .gif images to only refresh the bits that change, and you can see in the layers menu that the rest of the image is blank.

D'Eyncourt · 2009-03-19 6:02 pm

Iritscen wrote:
I actually do own GraphicConverter, although I never used it to make a GIF. I'll have to give it a try tonight. On the subject of the GIF that I thought used partial refresh, I had already stepped through it in GC, and it shows each frame in full. Since I didn't know what this meant (i.e., does GraphicConverter layer each partial frame over the previous onscreen as you advance through frames, or would it actually show the partial frame?), I couldn't learn anything from the exercise. If I only had a GIF that I knew used partial refresh, I could see how GC displays it. Or are you certain about that part?

Fairly certain, at least with those animated GIFs I created using GC. When I looked at those which had a partial refresh, the only part showing was the modified portion while the remainder of the frame was white.

On the other hand the maker of GC is fairly responsive to feature requests/modifications, so it is likely that perhaps you have turned/left on the feature which would overlay the changed sections over the previous image. I don't know for certain that such a feature exists--it has been a while since I last played with GC--but it seems to me that that would be an option to include.

Forums | MacLife

#1 2009-03-19 1:30 pm

Any GIF experts out there?

#2 2009-03-19 4:01 pm

Re: Any GIF experts out there?

#3 2009-03-19 4:24 pm

Re: Any GIF experts out there?

#4 2009-03-19 4:32 pm

Re: Any GIF experts out there?

#5 2009-03-19 6:02 pm

Re: Any GIF experts out there?

Iritscen wrote:

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