How to get high-res DVD screen grabs/captures
August 21, 2006 7:54 PM   Subscribe

Is there a way to get high resolution DVD screen grabs?

I'm looking for a way to capture images from a DVD, preferably in TIFF format (but jpeg will do in a pinch). These are images that will eventually be printed, so the higher the resolution the better. Printers request at least 300 dpi for sufficient image quality. But, in playing around the software I've found (in part through previous MeFi threads) such as PowerDVD or WinDVD etc., the best I can seem to get is 96 dpi. Any advice would be greatly appreciated.
posted by mollymolo to Technology (14 answers total) 3 users marked this as a favorite
 
Try using VLC.
posted by oaf at 7:57 PM on August 21, 2006


DVD frames are stored as 720x480 pixels (or 720x576 in Europe and other places), which at 300dpi is 2-3 inches across. You're never getting to get anything better than that, since the information simply isn't on the disk.
posted by cillit bang at 8:00 PM on August 21, 2006


Even worse, 720*480 is 3:2, and no video source is actually 3:2. So it's always necessary to do an aspect-ratio change, usually either to 4:3 or to 16:9. Such a resize will make the image less crisp.
posted by Steven C. Den Beste at 8:20 PM on August 21, 2006


DPI is entirely self-settable (that is, if you're talking about JPG, and, I believe, TIFF, there is no dpi information in the image). PowerDVD and WinDVD aren't giving you 96 dpi images, they're giving you 720 x 480 images, which are being displayed on your screen at 96 dpi because your monitor is a 96 dpi monitor. Print them on paper at 96 dpi, and they'll be the same size (roughly) as they appear on your screen. Print them at a higher dpi, and they'll be smaller than they appear on your screen. Print them at a lower dpi, and they'll be larger than they appear on your screen. DVDs only offer 720x480 images, so if you want a big printed image at 300 dpi, it isn't going to be possible, not because of a problem with the image ripping end, but because there just isn't enough image resolution on a DVD in the first place (this is why blu-ray and HD-DVD are being developed/released, because nowadays TV screens can show more than 720 x 480, and thus people will notice that there just isn't as much detail as they expected on DVDs)
posted by Bugbread at 8:28 PM on August 21, 2006 [1 favorite]


I'm a user of PowerDVD and it turns out that it doesn't necessarily do a raw capture. It depends on how it's set up.

I also recently noticed that if you have de-interlacing enabled, the frame grabs are considerably more blurry and less crisp than they should be. I've been doing some experimenting to see if I can find a manual setting which doesn't cause that, and the best I've found is "based in bitstream flags, bob".

But to really get the best result, you need to turn deinterlacing off entirely.

The other point is that the screen grab may not be 720*480. That's one of the choices, but it isn't the default. The default is "screen resolution", which is either 720*536 or 960*480 depending on the aspect ratio of the original source.

There are two problems with those: first, they're resized, which means they're a bit more blurry. Second, neither of them is actually precisely the correct aspect ratio, because the program wants its screen sizes to be multiples of 16 pixels, for some strange reason.

You have to deliberately choose "Original video source size" in order to get raw 720*480 images.
posted by Steven C. Den Beste at 10:24 PM on August 21, 2006


Sorry, Steven C. Den Beste points out something I totally glossed over: saying that PowerDVD or WinDVD aren't the ones responsible for the 96 dpi issue does not therefore necessarily mean that they're providing the best images possible. They may be providing bad images, because of deinterlacing, resizing, or the like. I don't know. My comment was purely that the 96 dpi issue is not due to them.
posted by Bugbread at 10:59 PM on August 21, 2006


Don't forget aspect ratio when making these grabs. Computers use square pixels, TVs use rectangular pixels. You'll have to adjust or the images will look slightly distorted.
posted by adipocere at 6:49 AM on August 22, 2006


Another thing to consider: DVD's, these days, *may not be interlaced on disc*. They're coming from film, and lots of DVD players understand how to do progressive scan these days.

So *that* may be why deinterlacing would be bad, when intuition would suggest that it shouldn't be: the program material may not be interlaced in the first place.

Depending on how hardcore you are about this, it might be worth your while to look at using DVD Decrypter to pull the MPEG2 files off the disc, and VirtualDub to see how they're actually built, and pull out the pieces you need.
posted by baylink at 7:33 AM on August 22, 2006


I made a slight mistake up there; for 16:9 DVDs, PowerDVD's screen size is 960*536, which means it's resizing both dimensions. (It ought to be 853*480 but it isn't possible to get that dimension even by manually resizing the window.)

When I want the crispest possible images, because nothing else will do, I've been using a real half-assed way to get them. I use a program called "Vidomi" and do frame grabs from it using Thumbs Plus. It sucks, but it works.

Vidomi's preview selection frame does no untoward processing of the video at all; what's in the MPEG is what you get. But Vidomi doesn't like encryption, so I also have to rip the DVD using a program called "SmartRipper". (I said it was half-assed, didn't I?)
posted by Steven C. Den Beste at 12:20 PM on August 22, 2006


Thanks everyone-- it's not the quick and easy answer I'd been hoping for, but you've been highly informative!
posted by mollymolo at 6:16 PM on August 22, 2006


as it turns out, even progressive video is interlaced on the disc. it's just that the two interlaced fields are from the same progressive frame, and its trivial to reconstruct the progressive frame from those two fields.

the reason they do this is that if the source material is 24fps and needs to be displayed at 30fps (60 fields/sec) its much easier to have progressive frame interlaced, since as part of the pulldown process you'll have to mix fields from one frame with fields from another. probably 90% of the display devices in the world are plain old television sets, which require interlaced video.

you can use mplayer to make screenshots, and they will come out great. if the video is film source, then mplayer will figure it out and "deinterlace" the video. if its video source, then you need to run with -vf lavcdeint or -vf pp=lb to deinterlace the video.
posted by joeblough at 12:42 AM on August 23, 2006


the reason they do this is that if the source material is 24fps and needs to be displayed at 30fps (60 fields/sec) its much easier to have progressive frame interlaced, since as part of the pulldown process you'll have to mix fields from one frame with fields from another. probably 90% of the display devices in the world are plain old television sets, which require interlaced video.

I don't know about that. I've seen files, which I've played with mplayer, which said they were 24fps. That suggests to me that they were ripped from a DVD wherein they were recorded at that speed, expecting the *player* to do the 3:2 pulldown and interlace -- though I don't know enough about player hardware to know if that's practical
these days or not.

More importantly, if they did that, they *couldn't* do the 3:2 pulldown before mastering, and therefore the disc *wouldn't* play properly on a 30fps playback chain.
posted by baylink at 4:33 PM on August 23, 2006


that's what i was trying to say. the player is responsible for the 24->30 frame rate conversion. that way if you have a progressive display, there's nothing to do, just reassemble the fields into one frame and ship it to the display. if you are running against a plain old TV, the dvd player then has to do the pulldown.

believe me, i know of what i speak :) anyway you can look it up for yourself with google.
posted by joeblough at 5:34 PM on August 23, 2006


by the way, if you watch mplayer carefully you'll see that it starts out at 29.97fps and then when it sees enough of the right flags in the mpeg headers it figures out that what's coming off the disc is actually 23.976fps and switches the framerate.
posted by joeblough at 5:36 PM on August 23, 2006


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