Fringing on PNG sequence output

LongJohn wrote on 10/26/2017, 9:37 AM

Hi all,

I'm using very clean imported alpha transparent elements within a project. To be clear, these have not been cut/masked out but are imported elements from 3D package that have pin sharp vector edges. They look fine on screen. On output to either PNG sequence, QT PNG , or AVI + transparent alpha - the output has a consistent dark fringe. I have seen other back-chat about this on web. It's never bothered me before but client wants a clean output set and I'm a bit stuck now after doing weeks of complex editing on some technical media for a medical client.

I have checked all my settings, but it seems the Vegas render engine is just fringing the alpha mask. It does this on single image screen grab frames as well, which is rather damning.

Any bright ideas folks?

Comments

john_dennis wrote on 10/26/2017, 10:16 AM

Since you have a folder of .png examples, could you upload one to a cloud drive and share the link here? Don’t upload it to this site as it will be manipulated for display.

Former user wrote on 10/26/2017, 10:30 AM

Are you rendering using the GPU?

LongJohn wrote on 10/26/2017, 11:20 AM

No - not using GPU. Despite my best efforts over the years buying in he latest video cards, this generally causes nothing but pain, so I tend to switch it off! This certainly is not coming off GPU render though. Fair question about sharing files but unfortunately files are all under signed NDA as they're for commercially sensitive biomed project. When I get a chance - probably not this week - I can reproduce the effect with something else but this is clearly something that hasn't escaped the notice of other Vegas users. I have used PNG sequences for year too, so not something that you'd notice unless you were working on particularly fine detailed work. Currently we've started re-mastering this in AE - from where it outputs fine - but I still need to find a solution to this. It almost looks like the Vegas software is feathering/pre-multiplying the edge by a couple of pixels for some reason - OK on mid-tones but awful on white.

Musicvid wrote on 10/26/2017, 11:42 AM

It almost looks like the Vegas software is feathering/pre-multiplying the edge by a couple of pixels for some reason

Is bit depth resampling or chroma subsampling going on? A 10 bit to 8 bit per channel conversion perhaps? The reason I ask this is my Vegas 8 uses a pattern dither which can cause edge interference in a few cases.

If I hand off 10 bit from 10 bit source, the downstream client may handle the 8 bit conversion with less interference. My takeaway from a recent discussion is that newer Vegas will output 16 bpc PNG.

Is there any scaling going on from source to project to output? Are there any unnecessary effects in the filter chain? High pass filters, such as Sharpen, will leave piping even when set to 0.

Is the alpha channel in your source compressed or uncompressed?

LongJohn wrote on 10/26/2017, 12:17 PM

Hi - and thanks for input so far guys.

No re-sampling - straight in at full HD, no filters at all apart from 10% lift on Levels white point. All Alpha uncompressed throughout. The mystery is that it seems to be coming off the rendering as it looks 100% fine on screen. I was hoping that AVI with lossless alpha channel might cure it, but exactly the same effect as on all the transparent options - which suggests to me that I'm either missing something or there's a bug in the rendering engine. I've used Vegas for 15 years for technical media, so I'm not new to the software - which I still really like BTW. The rendering sophistication of the suite seems to be getting a bit left behind though, which is a shame....

Musicvid wrote on 10/27/2017, 1:22 AM

I look forward to seeing your non-proprietary samples.