Forums > Jitter

still image with alpha over video


alexandra Verhaest
July 27, 2013 | 3:11 am

Hi all,

I’ve got a still image which I want to trigger to appear on top of a video layer. I’m a bit at a loss as to how to do this as processor-friendly as possible.. as for now, I have tried using jit.alphablend and rendered my still as a .mov with an alpha channel.. but nothing happens. I am quite the n00b… so I guess there is an obvious simple processorfriendly way to do this… can anyone point me into the right direction?

Thanks!
Alex


Christopher Dobrian
July 27, 2013 | 8:35 am

You can find some antiquated-but-still-essentially-correct examples on this page:
Programming Examples
Scroll almost all the way down, to the patches labeled "make a mask image", "mask by multiplication", and "mask by alphablend". See also Jitter Tutorial 29: Using the Alpha Channel.

The same effects can be achieved in GL with more efficiency, but if you’re new to Jitter I recommend the above methods first (which it seems you’re already attempting).


LSka
July 28, 2013 | 1:09 am

you don’t need to render your image as a .mov, as jit.qt.movie loades image files (PNG, which supports alpha, is your choice).


alexandra Verhaest
July 28, 2013 | 6:57 am

Hi there!
Thanks for the replies!
I have used the alphablend-patch from the mask-tab of it’s helpfile for now. Below is the relevant part of my patch. I’ll give png a try indeed.. but would this be the most lightweight solution to my problem? The image that needs to be masked upon the main movie is actually tiny.. about 10×10 pixels.. Is there a way to map a smaller image with alpha onto a bigger one and use coordinates to get it in the right place?

Cheers!
Alex

<code>

– Pasted Max Patch, click to expand. –

</code>

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