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 <kraxel@xxxxxxxxxxx> 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. > > > > _______________________________________________ > Video4linux-list mailing list > Video4linux-list@xxxxxxxxxx > https://listman.redhat.com/mailman/listinfo/video4linux-list >
