Hi A little bit of context for the situation which prompted me to send in this mail. I need to perform 'digital zooms' on segments of the image, and since the app is a real time thing would like it to be as efficient as possible. So the policy i thought of using, since V4L doesnt support this, was to scale and crop, which is why i needed to do clip the image. I would welcome any ideas on a way around this, or otherwise i guess working on the bttv2 driver for this feature might not be a bad place for me to start with. :-) Abheek On Mon, 27 Nov 2000, Justin Schoeman wrote: > Trent Piepho wrote: > > > > On Mon, 27 Nov 2000, Justin Schoeman wrote: > > > > Save PCI bandwidth? If you only want a fraction of the image, it doesn't make > > sense to DMA the whole thing into memory. > > OK - That makes sense. > > > You could also do memory overlay. Place a background image into memory, then > > overlay the video on top of it. Without clipping, a second copy is required to > > put the background into memory. For example, on-screen captions usually stay > > on screen for many frames, so they can be read. If memory overlay can't clip, > > you would have to redraw captions every single video frame, which is a lot of > > extra work. Of course, everyone but me has a 1 GHz or faster processor and > > doesn't care about a few lost frames, so efficiency issues don't seem to > > matter. > > The mmap()ed memory area is definitely NOT guaranteed to be user > writable, so this would not be a good idea. > > > Also V4L and V4L2 have no concept of adjusting the analog TV timing > > parameters. A crude workaround is to scale and crop the image to trick the > > driver into giving the desired timing. This won't work for non-overlay > > capture. > > OK v4l2 does have "digital zoom" capabilities that can let you select a > rectangular subpicture. I have not implemented it for bttv2, but if > anybody wants to, they are welcome!
