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Superimposing two images, both at 100% opacity

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james mills
Superimposing two images, both at 100% opacity
on Jan 18, 2013 at 9:27:19 pm

Greetings! This is my first post here. It looks like a very helpful community.

I'm sorry if this has been covered before, but I searched and could only find one thread about it, and it was inconclusive...

Is it possible to have two layers, on top of one another, both at 100% opacity? I am envisioning a simple B&W high-contrast image overlayed on top of another similar image, so that when they intersect, the blacks of the two layers look like they are connected.

Simplified example: A vertical black line segment on one layer moving from left to right, and horizontal line segment moving from top down. They meet in the middle and look like a black plus sign. If you had them at 50% opacity each, it would look grey.

It's a bit confusing to explain - sorry! Thank you for any help you may be able to offer.


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Mark Suszko
Re: Superimposing two images, both at 100% opacity
on Jan 18, 2013 at 9:52:46 pm

To do what you are talking about, each of the two images would need to be saved in a format that supports alpha channels. .psd, .tga, .tif. and .png formats can contain alpha channels in 32-bit mode.

Alpha channel is where the image stores the transparency data. So in your example, think of the two image layers as each being made of transparent glass, with an opaque or translucent decal in the middle of the glass. As you move the pieces of glass past each other, yes, the non-transparent layers will interact, the degree of interaction depends on not just the opacity of the layer, but on the composite or "blending" mode of each layer.

So go try making the two pieces as 32-bit targa files in photoshop, be sure to preserve alpha channels and layers when you save... import them into Final Cut, and tell us your results. You will want a white or gray background layer on video track 1, then your next two layers get the graphics on them.

Good luck!


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james mills
Re: Superimposing two images, both at 100% opacity
on Jan 18, 2013 at 10:22:02 pm

Thank you! I don't understand all of that, but I'm not the one doing the technical work anyway. I will relay this to my friend who is helping me.

What you are saying makes perfect sense! Basically, if the backgrounds of the images aren't "transparent", then white on one 100% layer (which I would need to get the black as black as possible) would block out black on another, etc. Yes indeed, we are talking about two black shapes on otherwise transparent layers, interacting over a separate white background.

Thank you so much! I will report back when I get it done -- or if I get into trouble!

Thanks,
Jim

P.S. If you look at this video (http://www.youtube.com/watch?v=WymhVug6Wns), with its superimpositions, is there anything special happening? Is the digital equivalent of this merely having four layers (4 band members) each at 25%? The images don't look that light, but maybe that's because since they're on top of one another, any places where dark parts interact have the effects of darkening the whole, so it looks pretty rich and colorful instead of too washed out.


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Mark Suszko
Re: Superimposing two images, both at 100% opacity
on Jan 18, 2013 at 10:53:41 pm

Saw the youtube link. To get that effect back in the day, four strips of film would have been run thru a machine called an optical printer, where a light would have been shined thru each layer one at a time onto a new negative. Once multiply- exposed, that negative would have been chemically developed and during that time as well as during the optical printing, the light parts would have been accentuated and the dark parks "crushed" or made darker. You can see a similar effect on your timeline if you lay four tracks of singers brightly lit against black limbo backgrounds, then altered by changing their blending modes. Try it, it's fun

Chris Gates does a nice job of explaining blend modes here:

http://www.digitaljuice.com/djtv/detail.aspx?sid=163


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james mills
Re: Superimposing two images, both at 100% opacity
on Jan 19, 2013 at 12:05:30 am

Wow! Some stuff to mentally process there. It's very interesting reading about the older methods. That's what I think looks the best in general anyway. (Not a Luddite, but...) Thank you again!


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