[PD] [GEM] Using masks with videos

[chris clepper]

>Anyone can help, please?

i'll give it a shot....

>----- Original Message -----
>From: "Armindo Dias" <arm_pdlist at yahoo.co.uk>
>To: <pd-list at iem.kug.ac.at>
>Sent: Thursday, April 03, 2003 8:21 PM
>Subject: [PD] [GEM] Using masks with videos
>
>
>>  I've tried the MaskDancer example and i would like to aply that to video.
>I
>>  want to have a video as the source pix and then another video as the mask
>>  piece. I tried to do this but all i gor was an empty image... is it
>possible
>>  to do masking with videos? And videos and images?

yes this is possible using alpha channels and pix_composite or you 
can try pix_chroma_key which doesn't require the setting of an alpha 
channel (it also works with YUV images).  pix_chroma_key takes a 
message for the "value" of the color to key with and a "range" which 
is a +/- offset to make keying a bit easier.  in the case of the 
dancer you would make the key value equivalent to white and give a 
small range to cover any pixel value differences and that should make 
the other image pop through the white part of the dancer image, with 
the black part  masking out the rest of the image,

>  And finally, do the two
>>  sources need to have the same size (like 400x300)?

yes.  there is no auto-scaling built into any of the objects.  the 
reasoning behind this comes from the idea that GEM gives up a bit of 
convenience for performance.  also that most people would 'tune' 
their patches to use the same image sizes to avoid the built-in 
scaling anyway.  pix_resize currently resizes an image to the next 
highest power of two, but could probably be made to work with 
arbitrary image sizes as well.

cgc