chris clepper cgclepper at gmail.com
Wed Sep 16 01:53:39 CEST 2009

On Mon, Sep 14, 2009 at 4:40 PM, Andres Ferrari <anfex at yahoo.com> wrote:

> hello, i am trying to use pix_mask with 2 movies.
> the movies were encoded in RGBA colorspace (codec planarRGB) for .mov
> files.
> but when I open the video the pd console show that is not possible use
> pix_mask with 2 YUV movies...

YUV has no alpha channel.

> maybe this objects works only with still images in jpg??

It works with movies in RGBA colorspace.

> maybe I need other codecs for my movies??

The 'None' codec will give uncompressed RGBA.  Or try Photo-JPEG at 100%
quality (any other quality level is YUV).

> maybe I have to create the movie with his own alpha channel??

The best way to use alpha channels is pre-render them in an off line app
like Photoshop or After Effects.  The alpha channel can hold any values, and
they don't have to be related to the image at all (alpha has no set meaning
in image processing).  pix_alpha just does a very simple average of R G and
B which might not give you the results you want.  You could do an extreme
setting for pix_contrast/saturation before it to remove all color
(saturation 0) and create black or white pixels with a very high contrast
value.  This would give a mask like the dancer.jpg used in the example
patches based on the brightness of the pixels.
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