Understanding dpi as it relates to Vegas

[Gary Kleiner]

[jsteinamite] “Why is it good to understand dpi in the context of video editing?”

DPI does not realy exist in video (what is equal to 1 inch?)
Better to get used to thinking in pixel hight and width.

Gary Kleiner

Learn Vegas and DVD Architect

http://www.VegasTrainingAndTools.com

[Randall Raymond]

[jsteinamite] “Now for dpi. Does it makes sense to lower the dpi of images in order to speeed up the computer even more?”

DPI is about scanning resolution. 720×534 pixels is what you need to create a graphic in Photoshop to fill a 4×3 screen. You can set the cropping tool in Photoshop and, regardless of the scanning resolution, you can crop a photo and arrive at those dimensions to fill the screen. Or create a new document in photoshop and drag your graphic into that and scale to fit.

Pixels are pixels, which is to say, they are measurements of real distance, like inches. But they are scaled, depending on the monitor or screen onto which they are shown.

Bottomline: if you scan to fill up the 720×534 space – you’ll do fine. That means small photos require a higher scanning resolution (like 300dpi) and large photos will do fine with a lower scanning resolution. A typical snapshot will work fine at 100-200 dpi.

Just remember those dimensions. Wide screen is 864×480 ntsc. Pal is a little different – but, then again, so are the French. 😉

[Mike Kujbida]

I’ll take a stab at it and see if I can clear things up for you 🙂

PNGs are lossless and therefore better – but not always necessary. JPEGS are fine for most work done in Vegas unless you need the alpha channel capability offered by the PNG format (or Photoshop’s native PSD format).
I rely on alpha channel capabilities primarily for titles & some graphics.
As I said earlier (this forum?), I save to the PNG format when I’m scanning simply because I know that I’ll usually be doing some touch-up work afterwards and don’t want to worry about multiple re-saves degrading the image.

On to dpi. I highly recommend reading (and understanding) Wayne Fulton’s website A few scanning tips. He does a decent job of explaining things in plain English.

In a nutshell, forget the term dpi. It’s a print term that has no equivalent in video.
By it’s very nature, video is pixel based and that’s all you need to worry about.

For scanning purposes (because most scanners relies primarily on dpi settings), my rule of thumb is that, at a scanning resolution of 100 dpi, 1″ = 100 pixels. Therefore a 6″ x 4″ picture scanned at a print resolution of 100 dpi will result in an image that’s 600 pixels by 400 pixels. This is a bit under the 720 x 480 resolution needed for SD (standard definition) video). Scan at 120 dpi instead and you have an image that’s (amazingly enough) 720 x 480 pixels (6 * 120 = 720, etc.)
Unfortunately 120 dpi isn’t a standard scanner setting but 150 dpi is. At this setting, your 6″ x 4″ picture comes out to 900 pixels x 600 pixels. This is more than necessary for video but, being larger, allows you to some mild zooming, panning and cropping if necessary.
Even to this day, in some NLEs & 3D apps, you have to be aware of aspect ratio differences between computer screens and video screens. In a nutshell, if you made a circle in something like Photoshop, you had to make the image (as I recall) 720 x 540 pixels in size so that when you brought it into your NLE, it would scale properly.
With Vegas, that’s no longer a concern as it scales the image to fit the desired output.

To recap, read Wayne Fulton’s site as he does an excellent job of explaining this rather confusing issue.

[Jsteinamite]

Hm. Sounds like there’s concensus on this. But given that I’m working with stsills and not actual video footage, does it still not apply?

Jonathan Stein

[Jsteinamite]

Scratch this comment. I replied before I read all of your responses. Thanks for all the clarification!

Jonathan Stein

[Andrew Jezierski]

I am a bit confused here when comes to widescreen. What should I scan at: 864:480 to fit my images into widescreen? BTW why Vegas shows my widescreen parameters as 720:480 widescreen and not 864:480?

[Andrew Jezierski]

To add to my previous question: does the scanning pixel ratio changes for vertical vs. landscape image orientation?

What is the best procedure to scan photographs for use in Vegas. I would like to crop the photos and do zoom and pan. Should I first bring them into Photoshop to crop? Or can I easly do all this directly in Vegas?

[Edward Troxel]

I just scan all pictures at 300dpi. This gives me plenty of pixels if I want to zoom in. Don’t worry about the width/height you actually scan.

Once you drop the image on the timeline, open Pan/Crop, right-click the image in the Pan/Crop window, and choose “Match Output Aspect”. Now you can resize the Pan/Crop screen as needed for the image and even add pans and zooms as desired.

Edward Troxel