video display wonkiness

June 15, 2005 10:44 AM

Sometimes my computer displays splotches of grey or white on something meant to be black.

In working on a website, I noticed some of the jpgs had bits of white scattered throughout something that was actually black--e.g. reflections on a pond, shadows, someone's hair. At first I thought it was a Firefox bug, but trying it in IE showed the same thing. Viewing it on a different computer didn't. Opening the images in Irfanview did, but moving the program around the screen changed what those places displayed as, based on what was in the program *behind* it: black over dark objects, grey over text, white over a white background.

Rebooting the computer made the problem stop, but I've (unintentionally) reproduced it twice now. Both times it seems to have been caused by leaving the DVD player open and paused for a long time (e.g. long enough to go cook, eat, and wash the dishes).

I tried taking screenshots, but opening them after a reboot shows them to be perfectly normal.

So ... obviously to avoid the problem I should not leave the DVD player open and paused for a long time. But what's going on? Is it a driver problem? Incorrect monitor profile? Something relatively harmless, or should I expect my video card and/or RAM to fail soon?

Sorry if this has been answered before; I've missed it if so (and had no look at the altar of Google).

posted by Tuwa to computers & internet (4 answers total)

Your DVD software (and other overlay software) uses a palette colour which it replaces with the video on the video card.

This causes anything displaying that particular colour to be transparent. If you can figure out exactly what colour that is for your software, you should be able to create a gif in your photo softs that will show the video.

Odd eh? :-D

It's totally normal, though.
posted by shepd at 11:10 AM on June 15, 2005

What shepd said happens for two reasons: 1) to allow your video card to do part of the MPEG decoding (if it knows how), freeing up the CPU, and 2) to prevent you from doing a screen capture to get images from the DVD, an anti-piracy measure.

If you want to avoid this, use VLC to play your DVDs, I believe it doesn't use the overlay function, or at least can be configured not to.
posted by kindall at 11:14 AM on June 15, 2005

The inability to capture pictures from video overlay is purely a limitation of some screen-capture software, most of which is just not smart enough to consider overlays. It's really not an anti-piracy thing at all. Who's pirating screen-shots?

Overlays are just an extremely efficient way to display moving pictures by letting the video card do the work, like you said.
posted by odinsdream at 12:32 PM on June 15, 2005

Who's pirating screen-shots?

Well, if you pirate them at, say, thirty screen shots per second...

It was a big deal before content scrambling got cracked; I believe it was in the contract with the DVD consortium that computer-based DVD playback had to have some kind of protection against screen-scraping. There's really no reason to use overlay if you just want the card to do some of the work; cards could just be designed to decode MPEG directly into their primary VRAM instead of into a separate overlay bank.

The point's moot now, of course, but I'm sure the clause is still in the contract.
posted by kindall at 3:34 PM on June 15, 2005