Jonathan, There's 2 ways I've used to do it. The first is to use a filter to remove the background (you would need to have the camera pointing at a plain coloured background though) and in the filter just compare to see if the green component is much higher than the other components, and filter on that. Noise is still an issue, but it can at least be reduced a bit.
The other way is to do motion detection, and remove anything not moving. To do that I just used a queue with a length of 2, so I could feed the current and last frames into a filter. It's fairly easy to mask out the background, but there are some quite nasty catches. Video noise is a huge problem, as it means the whole image is always moving slightly. You really need a good camera to get rid of it, otherwise you have to do a lot of noise reduction that can make the image look blurry. Another big problem is auto-white balance on the camera, or anything like that.. if the camera suddenly adjusts anything, the whole image changes so the background suddenly pops into view for a short time. Again, a good camera with manual controls would help. The last problem is that sometimes the thing you want to show stops moving. Say you're filming somebody talking.. their mouth is moving, but their eyes might stay still for a short time. They disappear.. and even if they are moving constantly, sometimes there will be an area with similar colour that doesn't get detected, and you have a hole.. I guess the way ichat works is to sample the background just once, when there is nothing in front of it, and use that for comparison. Then even if you're still, there is still a difference. You still have the problem of white balance changes, video noise etc., though so you'll need a fair bit of cleaning done on the image. Chris 2009/1/16 Jonathan Selander <[email protected]> > Hi, > > I've used a couple of patches from the QCTV example application to create a > green screen effect in my composition. However, i just compared it to Photo > Booth which does it much more accurately. What's the best way to accomplish > this? Is there any patch out there i can use that works well? > > The QCTV patch seems to be very susceptible to video noise, so lots of > pixels appear everywhere, so the backdrop isn't solid. > > Thanks > _______________________________________________ > Do not post admin requests to the list. They will be ignored. > Quartzcomposer-dev mailing list ([email protected]) > Help/Unsubscribe/Update your Subscription: > > http://lists.apple.com/mailman/options/quartzcomposer-dev/psonice%40gmail.com > > This email sent to [email protected] >
_______________________________________________ Do not post admin requests to the list. They will be ignored. Quartzcomposer-dev mailing list ([email protected]) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/quartzcomposer-dev/archive%40mail-archive.com This email sent to [email protected]
