Multiply (mask) video track problematic results

mjr wrote on 10/31/2008, 5:03 PM

Hi! I have Vegas Pro 8.0c and this problem:

When I set the video track to "Multiply (mask)" compositing mode and put into the track some mask media - for example white solid color - the picture of the track below is visible as expect with normal levels. If I render it as DV (I use DV PAL) for example to the new track, the processed picture has boosted contrast. But there's no level corrector used in the way.

This occurs even if I make a blank "Multiply" video track compositing child of another blank video track. The picture of the tracks below has expanded contrast AFTER rendering.

I have the same problem if I use "Custom" compositing mode as a "Bump map" etc.

Is this a bug? What I may do to keep original levels of picture below the mask?

Comments

mjr wrote on 11/21/2008, 6:14 PM

I reply myself:

There was unchecked "Ignore third party DV codecs" in the Preferences -> General tab. So Vegas used MainConcept DV codec during rendering. This codec didn't accept sRGB wide gamut.

This makes different output levels and increases contrast after all rendering to AVI file.

Solved.

Grazie wrote on 11/21/2008, 11:41 PM

mjr, or anybody, could you please explain further? I think this is fascinating, relevant and would like to understand this with a bit more surety than I am at present?

It is more to do with your "setup" of the tracks and compo work than your fix? Could you supply a screen grab of the timeline?

Getting more dynamic and "stretch" in my work from my footage is what I am continuing to explore. What you are outlining I could very well add to my arsenal of CC and C Grading.

Cheers

Grazie

farss wrote on 11/22/2008, 1:49 AM

I just tested this and I can't see anything wierd going on at all.

Multiply pretty much does an arithmetic multiply. White = 1, Black = 0. Results are kind of obvious. The white parts of the mask let the track below 'shine' through untouched. The black of the mask ends up transparent and greys appropriately in between. Contrast is not changed. I tried this with a grad + white, scopes don't move at all.

The only thing one could argue is that Vegas kind of gets it wrong as it defines White as 255,255,255. If you multiple by 'legal' white (235,235,235) then you do reduce the contrast of whatever you're masking. I can't see anyway that a Multiply Mask can increase contrast at all and from what mjr said above this wasn't what was happening.

Masks are very usefull for CC work but only when used in conjunction with the traditional CC tools. The compositing modes of Add and Subtract can be used to Add or Subtract color without using gain and hence increasing noise.

Bob.