72dpi is not the accepted DPI for SD video as DPI has absolutely nothing to do with video. It's all about the dimension of the image in pixels. (DPI only comes into play when scanning and printing. If you scan a 4" x 6" image at 300 DPI, then the image will be 1200 pixels by 1800 pixels. if you scan at 600 DPI then the image will end up a 2400 pixels x 3600 pixels.)

Anyway, 720x480 is the resolution of NTSC DV-format video, but it's based on rectangular pixels. Scanned photos, photos from a digital camera or graphics you create on a computer are based on square pixels. If you resize a digital scan, photo or computer-generated graphic to 720x480, the aspect ratio will be wrong. Circles will no longer be circular.

However, Vegas is smart enough to compensate for square vs. rectangular pixel formats, it assumes that all images are square pixel. (But you can change this under the images properties in Vegas.) If you crop or resize your photos then it's best to make sure they are no less than 720 pixels in the horizontal dimension and no less than 540 pixels in the vertical dimension. Vegas will scale them down to fit and compensate for square vs. rectangular.

It is always better to resize an image down in size rather than up. When you resize down, you are throwing information away. When you resize up, you are having to interpolate (guess) and create information that is not in the image to begin with.

John

A good writeup. A couple of points though. The recommendation of 720x540 is based on a standard but erroneous calculation method established long ago based on the assumption that 720x486 = 4:3 frame ratio. Vegas engineers did their calculations based on sample rates (it was an audio application, after all) rather than this assumed ratio. Vegas is technically right, but it doesn't agree with the wrong calculation that everyone else uses by convention.

Vegas creates corrected NTSC DV stills at 654x480. If you pop that into photoshop and scale it back up to 720px wide you'll get an image that is 720x528. You can use that as a base dimension for stills you bring into Vegas from cameras and scanners, assuming your project is NTSC DV.

Vegas's practice of outputting stills from video frames is to maintain the vertical dimensions of the frame and then to adjust the horizontal dimension. This preserves interlacing but, at least for NTSC, throws away some of the horizontal resolution. Overall, it's a policy of treating all stills as having "Square pixels", which makes life easier for users but has its own tradeoffs.

This is somewhat off the topic of DPI, but John and I are emphasizing the idea that with a little thought you could do a slightly better job handling stills that Vegas's default workflow would give you. The problem with this for most users is there are a lot of "if..then" situations here that a user could just skip by doing everything as the Vegas manual instructs.

Rob Mack

There is no accepted dpi for SD video or any other video. The dpi setting for a still image *has* to be set to something, so Vegas chooses 72. It could just as easily have chosen 300 or 3 or 74.6 or 0 or 9218.37982. It makes absolutely no difference at all, because inside video it means absolutely nothing at all.

Here's some relevant reading on the topic:http://www.scantips.com/no72dpi.html

Rob

Actually that guy went a little two far. DPI does matter on the computer screen when using page layout software. Most page layout programs will honor the DPI setting when first scaling an image to the page. Of course, the user can easily stretch the image out or shrink it, but when the image is first dropped on the page it will usually use the DPI setting to figure out how big it should be on the page.

Then again, video NLEs aren't page layout programs.

I BIT till blood came to half finish reading the NO72dpi and know , ENGLISH is damned difficult for english people. am luckily chinsky.

Rob, you're absolutely correct, it is 720x528. I guess I've spent too much time dealing with 720x486 video!

"DPI is totally irrelevant to video."

I'm not so certain anymore!
Did a job for client who comes from a graphic arts background and works mostly for agencies these days doing TVCs. He was kind of taken aback when I told him how silly this 72dpi thing is. If I understand this and why that figure is used so much it's because that's how the image looks on a SD TV. In other words when the client wants to know how the shot of his product that cost him serious money to get it going to look on the viewers TV then the figure of 72dpi does make a lot of sense. In other words it's a metric that they can understand, it's not going to look as good as it does printed in a glossy magazine.
I just mention this aspect because as I've found out sometimes you've got to learn to talk the other guys language, in this case it's easier to go with the flow, do a little maths and say yeah 72dpi at 8x10 will do me nicely for SD.

Bob.