Moho Forum

i have a little problem
i imported to my moho project a mov video. I think it has alpha channel but im not sure, mostly because when i render the animation i see the backround of the mov video. How can i determine if the video has alpha channel. huh:)
thanks

here it is:
http://dns.4ce.hu/alvin/Explosion2.mov

I answered this question in the other thread, here:

http://www.lostmarble.com/forum/viewtopic.php?t=388

Now that I see the movie in question, I can say no, it does not have an alpha channel. Many video editors can extract an image from a solid-colored background, in this case black. Maybe that's how the movie was intended to be used. However, Moho does not have such a function - it relies on an alpha channel to indicate which areas should be ignored.

thank you for response

And how could i add alpha channel to this video? Can i?

Agent wrote:And how could i add alpha channel to this video? Can i?

That depends - how was it created, and do you have the option of re-generating the movie? It would be much easier if the alpha channel was added when the movie was created, rather than trying to add it later.

And how could i add alpha channel to this video? Can i?

Here's two of the techniques I've picked up along the way for replacing items or rendering hold-out mattes when rendering Alpha channels is too cumbersome or not available.

1) Use a luma matte in your compositing software. Basically a luma matte changes your image to an alpha channel. Simplified, if it's white it's not transparent (value of 1) or if it's black, it's completely transparent (value of 0). Varying shades of gray allow for varying degrees of transparency.

If you've already rendered your animation and need a new alpha channel, change the colors of your animation to white, black or shade of grey, bring it into your compositng program (like After Effects) and use it as a luma matte.

2) If I need to re-render just one element, but need it to pass behind something, I'll need a hold out matte, or a way to cut the character out accurately. Change the colors on the objects you don't want to show up to a solid color that doesn't appear elsewhere in your animation otherwise you'll end up seeing through your character, let's say neon green for now. Write down the RGB values, you'll be using them later. Be sure your background color matches this color, too.

Re-render your animation. You'll need an uncompressed render format (uncompressed, animation codec in Quicktime, or PNG, should all work). It will be your one item (object, background item, etc.) rendered on an all neon green background, with it being occluded by objects in the foreground in the same bground color. Bring your footage into your compositing program, and use the image keyer. Basically you're going to do a "green screen" extraction on your footage. Plug-in your RGB values from before and you'll get an exact cutout of your character. This works particularly well since the image keyer is using a very specific value and it doesn't change, unlike trying to pull green screen on live footage, which can be a huge pain in the keister.

This technique is most useful if you've decided to render in passes.

I hope this helps.

Kdiddy[/quote]
________
THE CIGAR BOSS

thank you
i'll try it