Re: [V4L] bttv: Scaling and Cropping

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]



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.





[Index of Archives]     [Linux DVB]     [Video Disk Recorder]     [Asterisk]     [Photo]     [DCCP]     [Netdev]     [Xorg]     [Util Linux NG]     [Xfree86]     [Free Photo Albums]     [Fedora Users]     [Fedora Women]     [ALSA Users]     [ALSA Devel]     [Linux USB]

Powered by Linux