Hi,
Thanks for raising this. It explains why something I digitized recently
after using VIDIOCSPICT to alter the contrast was so poor.
It is better to use is 180/254 (the ratio of the default register values)
than 201/283 which is an approximation to the range in percent.
On 26 Jun 2001 14:50:53 GMT
Gerd Knorr <[EMAIL PROTECTED]> wrote:
> Frank de Jong wrote:
> > Hi,
> >
> > For our project of soccer-playing robots, we use off-the-shelf WinTV
> > frame grabber cards to import from our Jai CVS3300 PAL cameras. We
> > noticed that the colors as displayed on our Philips PAL monitors were
> > different from the results from the grabber, using the Linux BTTV
> > driver. This is no big surprise in itself, but it led us to look into
> > the driver source code, and we noticed that a different gain is used
> > for U and for V in bt848_sat():
> >
> > /* 0-511 for the color */
> > val_u = color >> 7;
> > val_v = ((color>>7)*201L)/237;
> >
> > We looked in the BT878 PDF document (127 pages), and found no reason
> > for this factor. Can anyone explain what this factor is for?
>
> The ranges for u and v are different.
>
> u is 0 ... 201%, with 0xfe (100%) as power-on default.
> v is 0 ... 283%, with 0xb4 (100%) as power-on default.
>
> pages 113/114 in my copy of the pdf file.
>
> I'd say the 237 is a tyops, should be 283.
>
> Gerd
>
> --
> Damn lot people confuse usability and eye-candy.
>
>
>
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