On Wed, 15 Nov 2000, Alan Cox wrote: > > I would like to use the scaling and cropping features in the bt848 > > chipset. Are there any ioctls etc in the linux driver to allow me to do > > that (by setting the hscale/hactive register etc?). > > Define the display window the size you want the image. The driver wil scale > it to that size for you providing the hardware can do it For the bt848, and most other capture chips too, you can control the horizontal and vertical position of the image within the window. You can also control the horizontal scale of the image, without changing the number of pixels. The number of scan lines is more fixed, as you don't have to deal with the imprecise timing of the horizontal section of the scan line. If you ask for 480 active scan lines, you get should 480 lines. Ask for 640 active pixels, you might get 635 active pixels and 5 inactive pixels. For instance, the NTSC hscale/hactive values in the bttv's tvnorms table are wrong. They're not the same as in the datasheet, and result in a black band on the left because the front porch isn't long enough. Even if they're fixed to the correct values, there is still fine tuning than can be done, but it's not some fixed amount. Even on the same channel, the exact position and timing of the signal changes between commercials. Unfortunately, V4L has no concept of these things, which is one of the larger omissions IMHO. I added two BTTV specific ioctl's for reading the writing the bt848 control registers, and then added timing parameter tuning controls, like the position/size controls on a monitor, to my TV program.
