ADOBE AFTER EFFECTS: Forum Expressions Tutorials Creative Cloud

PNG alpha issue

COW Forums : Adobe After Effects

<< PREVIOUS   •   FAQ   •   VIEW ALL   •   PRINT   •   NEXT >>
David Johnson
PNG alpha issue
on Jun 26, 2010 at 4:18:08 pm

I've got a strange issue all the sudden that I've never seen before and would appreciate any ideas about why it's happening and, more importantly, how to fix ...

The alpha channels in all my PNG MOV renders no longer show up properly. I use a 50% grey background to render MOVs with alphas (instead of the default black), but the alphas look like they have a semi-transparent black over them and what should be soft black shadows appear as whitish outlines. So far, the alphas seem to function properly if I re-import them and lay them over something, but they look wrong when the MOVs are opened independently of AE.

This is in AE CS3 (with all updates & the most current QT) on the same XP machine that I've rendered very many PNG MOVs in the past couple years without this ever happening until a week ago. There haven't been any changes to the system and I have a second machine with the same exact setup, but it isn't happening on that one.


Return to posts index

Todd Kopriva
Re: PNG alpha issue
on Jun 26, 2010 at 5:28:14 pm

What you described sounds like the difference between straight and premultiplied channels. When you look at an image with straight channels by itself, it looks wrong as you described, but it works fine when composited---which is what matters, right?

---------------------------------------------------------------------------------------------------------
Todd Kopriva, Adobe Systems Incorporated
putting the 'T' back in 'RTFM' : After Effects Help on the Web
---------------------------------------------------------------------------------------------------------
If a page of After Effects Help answers your question, please consider rating it. If you have a tip, technique, or link to share---or if there is something that you'd like to see added or improved---please leave a comment.


Return to posts index

David Johnson
Re: PNG alpha issue
on Jun 26, 2010 at 6:33:31 pm

Thanks Todd.

[Todd Kopriva] "it works fine when composited---which is what matters, right?"

Yes, but I'm making a bunch of individual graphics at home that I'll later composite in FCP at work so I need to be able to check my work accurately.

And, I'm using the same custom render settings and output modules I've always used, which are set to premultiplied, so why would I be getting straight channels all the sudden when I haven't changed anything?


Return to posts index


Todd Kopriva
Re: PNG alpha issue
on Jun 27, 2010 at 3:07:51 am

If you really haven't changed anything, then I don't know. But I'd check the Color menu in the output module just to be sure, to see if you changed it to Straight and forgot... or maybe applied a different template than the one that you think you did.

---------------------------------------------------------------------------------------------------------
Todd Kopriva, Adobe Systems Incorporated
putting the 'T' back in 'RTFM' : After Effects Help on the Web
---------------------------------------------------------------------------------------------------------
If a page of After Effects Help answers your question, please consider rating it. If you have a tip, technique, or link to share---or if there is something that you'd like to see added or improved---please leave a comment.


Return to posts index

David Johnson
Re: PNG alpha issue
on Jun 27, 2010 at 11:50:33 am

I really haven't changed anything. I've not only checked the output module before each of the dozens of renders I've done in the past week, but even deleted and recreated the output module, as well as reset the preferences. Perhaps AE's PNG codec has somehow become corrupted ... don't know what else to do so I'm going to try replacing it with the one from the identical machine tomorrow. Thanks.


Return to posts index

Kevin Camp
Re: PNG alpha issue
on Jun 27, 2010 at 11:37:35 pm

[David Johnson] "Perhaps AE's PNG codec has somehow become corrupted"

actually, if it is a quicktime png, then it would be apple's quitcktime png component that got messed up...

you did mention that you were rendering with a gray bg... i can see that being a problem for some software if you are rendering premultiplied. most software (or hardware) that will accept a shaped fill is expecting that shaped fill will be rendered over zero black. if it's not you can get a variety of results, from the halo/fringing that you described to a milkiness or haze over the areas that should key out. so i'm betting that the gray bg and shaped (premultiplied) fill are creating your problem.

if you want to test whether it is a format/codec or a setting, try a render using multiple output module, it will take a about the same time to render, but you can create several files to test.

i'd try one with your qt png and premultiplied settings. duplicate that, then try it as a png image sequence (this doesn't use the quicktime png component). i'd also try a lossless animation with color set to 'straight' and a qt png with color set to straight.

then see which ones key correctly in your software.

Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW


Return to posts index


cow
David Johnson
Re: PNG alpha issue
on Jun 28, 2010 at 12:31:40 am

Thanks Kevin.

They are in fact a QuickTime PNGs so it's a good point that it may be a QT issue. I have the same QT version on both of two practically identical machines ... the other doesn't have this issue and the one that does has only had it for the past week out of 2+ years.

I understand your point about using grey backgrounds for alphas so I do use zero black when I'm making something that'll go outside my typical workflow (wherein I'm the only editor and all the software & hardware is the same). Otherwise, I've used 50% grey backgrounds for all my AE graphics that have alphas for many years without any issues (so I can see shadows, etc. in the rendered files before composited). In fact, I've rendered hundreds, if not thousands, of graphics using the same exact methods, software and hardware in the past 2+ years, which was the last time there were any significant changes to anything about the three systems I use (I'm still using CS3 & Final Cut Studio 2 for a few more months).

I'll try some tests, but it's looking more and more like I'll just have to live with this for a few months until I upgrade to CS5 and FCS3.


Return to posts index

Kevin Camp
Re: PNG alpha issue
on Jun 28, 2010 at 11:50:06 am

i'm not an fcp user, but unless fpc lets you pick the bg color that the piece was rendered on, then i doubt that it will handle the soft or translucent areas on grey background correctly when the fill is premultiplied.

ae handles it because it can define the background (matte) color. if it mishandles it, you can always pick the correct color in the interpret footage settings, or with an effect like remove color matting (maybe something like that exists for fcp...?).

i would try a render with alpha using 'straight (unmatted)', i've never encountered an nle that doesn't handle that perfectly -- although i do work with hardware that requires it to be premultiplied on super black.

Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW


Return to posts index

<< PREVIOUS   •   VIEW ALL   •   PRINT   •   NEXT >>
© 2017 CreativeCOW.net All Rights Reserved
[TOP]