The problem with this method is that when you have black video (no setup in PAL video) you have no brightness to modulate. When you have maximum level, you have maximum contrast for the logo. This looks weird. Summation works better, with a logo signal that goes plus and minus. R Bob Ammerman wrote: > > Use a multiplying DAC. These take an analog input, multiply it by a digital > word and create an analog output. > > You could use a prepackaged DAC, or since you really only need a few > multipliers (for brightness levels), you could cobble it together with > discrete parts. > > Bob Ammerman > RAm Systems > > ----- Original Message ----- > From: "Jinx" > To: > Sent: Tuesday, February 03, 2004 6:08 PM > Subject: [PIC:] Watermarking video with a PIC or SX > > > I've been asked by a small production company whether it's > > possible to watermark a video with their company logo. My > > initial response was "probably", now I have to prove it ! > > > > I know a little about the format of TV scan lines (PAL in this case) > > > > http://www.epanorama.net/documents/video/pal_timing.html > > > > and woud like suggestions on how this could be accomplished. > > The only signal available is composite, as in that link's picture > > > > "Watermarking", as they describe it, is a shape on the picture > > created by altering the brightness. The graphic is translucent, > > rather than opaque super-imposed pixels. They also indicated > > that the watermarking should have several levels of brightness > > alteration to give it more depth. It'll be around 1" square in the > > bottom right corner > > > > As the graphic will be a known shape at a known position, I > > wonder if a fast video ADC can be used to measure the original > > pixels where the graphic needs to be and then use a look-up > > table in the micro to alter the brightness. Then it gets written back > > with a video DAC. As the whole line takes just 52us to scan and > > the area of interest is maybe only ~3us of this, that suggests to me > > that alterations will be seen one frame later. I can't see a micro > > being able to implement ADC > change > DAC in real time. A 50 > > or 75MHz SX could easily do the pixel timing I'm sure, although > > who knows what analogue conversion and switching problems > > are likely to appear > > > > But maybe someone has a better idea of how this could be done. > > Links to anything relevant would be appreciated too. I've already > > had a look at sites describing PIC- and SX-generated video signals, > > but it's not really the same thing > > > > TIA > > > > ============================================== > > Research is what I'm doing when I don't know what I'm doing > > - Wernher von Braun > > > > -- > > http://www.piclist.com hint: The PICList is archived three different > > ways. See http://www.piclist.com/#archives for details. > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.