[GEM-dev] 0.90 and pix_video under Linux

IOhannes m zmoelnig zmoelnig at iem.at
Mon Jun 21 12:15:08 CEST 2004


Mirko Petrovich wrote:
> 
>
>> probably your [color]/[colorRGB] is set to black ? (or the 
>> alpha-channel  is 0 ??)
>> thinking of this, it might be, that the video4linux-driver is able to 
>> produce RGBA-images but unfortunately sets the alpha-channel of each 
>> pixel to 0. in this case, you will have to raise it manually. 
> 
> 
> I checked this, and it's not the problem , the strange thing is that 
> alpha works in pix_gray and even in pix_yuv (I get a distorted image, I 
> guess this is right).

this isn't strange as [pix_grey] and [pix_yuv] use colour-spaces that do 
not have an alpha-channels (so it is automatically set to 1)
i still believe that the problem is, that [pix_video] returns 
RGBA-images with alpha=0 (you could watch this with [pix_histo]
furthermore, you can send a [colorspace YUV( or [colorspace GREY( 
message to [pix_video], which might be faster (depending on the 
video-capture-device)


> 
> I was calling pix-mixers (I forgot there was a pix_mix object) as a 
> generic name, actually I'm using compose,add,subtract,diff,compare, 
> chroma_key,mask, etc... and my idea was to fade the resulting image 
> textured in a lot of geos (with openGL-alpha blending).

i was just asking; could have been possible that you were only 
interested in simple mixing...


mfg.a.sdr
IOhannes




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