Forums > Jitter

Effects applied to selective parts of a matrix?

October 31, 2006 | 10:56 am

Hi
I’d appreciate any help with this. I know this has been done a lot, so if anyone can point me to a working example or set of patches, I’d be grateful.

I am using cv.jit objects with a webcam to detect a person/object. I would like to use the information to apply effects to a QT movie. At the moment I can use the numbers coming from the object’s presence to apply effects to an entire matrix.

But what I want to do is to apply the effects to the corresponding area of the matrix where the presence is detected. A simple example would be to saturate or brighten an area in which an object/person/hand is present.

I guess I could use scissors to cut up the matrix into tiny bits and apply effects to each separate matrix and then glue it all together again. I want the effect to move seamlessly across the movie as the object moves, so I’m not sure if this idea will work. If there is an interface out there that does this already, it would be very helpful.

Thanks!
Toni Olivier


October 31, 2006 | 11:27 am

My first thought would be to make two ‘instances’ of the movie you’re
applying the effect to which are layered on top of each other. The lower
one of the movie matrices is the plain movie whithout effects, the top one
the same movie but with effects.
Then use the data from your cv.jit objects to create an alphachannel which
cuts out the area of interest, for example the hand you mentioned.
Afterwards use this alphachannel to blend out (alphablending) the unwanted
parts of your top movie layer.

This should do what you’re trying to accomplish. It’s all quite vague i
know, but quite feasible. Also i’m not saying that this is THE solution, but
hey that’s kinda the freedom that developing stuff like that gives you for
starters… right?

anyhoo, If you don’t catch my drift i could set up a small example patch.
(… unable to do this in the first six hours, but afterwards this should be
no prob.)

cheers!
d

On 10/31/06, Toni Olivier wrote:
>
>
> Hi
> I’d appreciate any help with this. I know this has been done a lot, so if
> anyone can point me to a working example or set of patches, I’d be grateful.
>
> I am using cv.jit objects with a webcam to detect a person/object. I
> would like to use the information to apply effects to a QT movie. At the
> moment I can use the numbers coming from the object’s presence to apply
> effects to an entire matrix.
>
> But what I want to do is to apply the effects to the corresponding area of
> the matrix where the presence is detected. A simple example would be to
> saturate or brighten an area in which an object/person/hand is present.
>
> I guess I could use scissors to cut up the matrix into tiny bits and apply
> effects to each separate matrix and then glue it all together again. I want
> the effect to move seamlessly across the movie as the object moves, so I’m
> not sure if this idea will work. If there is an interface out there that
> does this already, it would be very helpful.
>
> Thanks!
> Toni Olivier
>


October 31, 2006 | 12:22 pm

Thanks for the quick reply – this sounds like an interesting approach. Unfortunately I’m not that experienced with Jitter to do this without help.
I would really love it if you could mail me off-list with an example patch! (toni dot olivier at gmail dot com)
Ta,
Toni


October 31, 2006 | 2:17 pm


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