Hi Ben I only tried full size, but the effect is that of a grid - but intermittent. The PCI latency idea seems reasonable as my PC is a bit skinny. I am familiar with the effects of interlaced fields - it is definitely more nasty than that. The effect is best described as getting a blotchy image with the blotches in the correct location and black in the gaps and the blotches fit into small rectangular zones so that repeated captures on a still scene gradually fill out the blotches to full rectangles but never completes the picture, leaving the dark grid. The horizontal lines get deeper going right at quarter width steps. The vertical lines are concentrated in the middle two quarter widths and are pretty constant over the full height. The rectangles are of the order of 16-32 pixels. Also I capture the whole image but am only delivering one field in my test. Cheers, and thanks for your attention Ivor ----- Original Message ----- From: "Benedict Bridgwater" <bennyb@xxxxxxxxx> To: <video4linux-list@xxxxxxxxxx> Sent: Thursday, April 19, 2001 3:45 PM Subject: Re: weird effects > Justin Schoeman wrote: > > > > Ivor Cox wrote: > > > > > > Further tests indicate that the data for a capture (I am using mmap) is > > > incomplete and confused by the remains in the buffer of the previous image. > > > The incompleteness has a pattern which results in the grid I explained - but > > > the image I get is a mixture of the latest and earlier images. > > > > > > If I have not waited correctly for sync or am reading the wrong buffer > > > (effectively the same!) would I get an effect like this? > > > > > > BTW the image I see is undistorted so I am sure the RGB format is correct - > > > it's just got bits missing in a near-regular pattern. > > > > > > Ivor > > > > This sounds like the PCI latency effects again. Try playing with the PCI > > latency timers in your BIOS setup. > > > > Hmm... > > Ivor, does this happen for all image sizes, or only above half size > vertical? Above half size bttv gives you an interlaced image where > alternate lines in the image are from the odd and even frame. I've seen > a problem before (do you remember Justin? - I sent you a test program > and you were able to duplicate it) where the DMA engine stopped > transferring one of the odd/even frames with the result that there > appeared to be a fixed ghost image in the background (odd lines in the > image) with the live picture (even lines) superimposed on that.. does > this sound similar? > > Ben > > > > _______________________________________________ > Video4linux-list mailing list > Video4linux-list@xxxxxxxxxx > https://listman.redhat.com/mailman/listinfo/video4linux-list
