Opacity changes colors

mjdog wrote on 5/13/2002, 2:56 PM

Yesterday I was attempting an effect where I start with a red rectangle (in tract 1) - that I created inside Vegas with the generated media - and with tract motion move it from the left-top corner of the screen toward the right bottom. On tract 2 is a blue rectangle moving from right-bottom corner to left top. I wanted both tracts to be transparent, and when they overlapped to appear violet (ie blue + red = violet). I thought this was going to be easy to do.

To make them transparent, I used an opacity envelop on each tract, but (and here's the problem), the opacity envelop changes the color, for example the red looks orange and the blue looks green! I played with the different settings in tract compositing (additive, negative, etc) but couldn't get the look I wanted. Isn't there a way to make a color semi-transparent without changing its 'basic' color?

Comments

SonyEPM wrote on 5/13/2002, 4:04 PM

One way to do this:

Put solid color A on track 1, solid color B on track 2.
Adjust track motion so the rectangles shrink and intersect.
Set compositing mode on track one to "difference"
Render to new track as uncompressed .avi.

Set the alpha channel for this newly created media to "premultiplied"- it will key out the black, so you can now overlay this on whatever video you want.

Cheesehole wrote on 5/13/2002, 5:02 PM

>>>the opacity envelop changes the color, for example the red looks orange and the blue looks green!

I just tried this and did not get your results. the blue is still blue when I turn down the opacity envelope. it's just darker, because underneath it is black.

SonyDennis wrote on 5/13/2002, 6:00 PM

I just tried this too, and they *don't* change color. Are you using an LCD monitor, they can sometimes "change color" with respect to brightness?

The "Add" mode does what you want, Red + Blue = Magenta (additive colors).

If you want to pick your *own* color for the overlay, to simulate paint mixing or something, there are a ton of things you could try, such as rendering out a "mask" of just the intersection (Multiply mode with white images) of the rectangles so that you can key in your own color using a mask track. If the motion is simple, you could generate this with "Solid Color" instead of rendering it.

Track 1: Rendered mask of intersection, to key track 2
Track 2: Child of 1, full screen generator of color of your choice
Track 3: Red rect
Track 4: Blue rect

///d@

MNJ wrote on 5/14/2002, 12:35 AM

Thanks for the replies. I figured out what I was doing wrong - I added a glow to each rectangle, and by default the glow color is yellow, thus changing my blue to green and my red to orange. Oh well....as they say, best way to learn is by your mistakes. Thanks for the other ideas.