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I have fought the battle of putting stills in video a number of times and have come to the conclusion that dpi doesn’t matter.
In still printing, you know the size of your output format and would normally scale your final to 300 dpi which has become sort of a standard. Of course, you’re not stuck with 300 dpi, but let’s use it for discussion’s sake. For example, if your output will be an 8×10″ print, at 300 dpi your file would be 2400×3000 dots or about 7.2 megadots or megapixels whatever you like to call it. Assuming your printer and paper can support that resolution, that will give a darn nice looking photo.
But, in video, you don’t know the viewer’s screen size, or even it’s resolution. What you do know is your project’s resolution. Let’s say it’s 1920×1080, a common standard. Notice that is only about 2 megapixels and that’s as good as it gets! To see what the displayed dpi is, calculate the screen dimensions for the desired screen size and divide the width by 1920. That tells how “thinly” the pixels must be spread to fill the screen area. These are: 32″ diagonal screen is about 28″ wide by 16″ high which gives about 69 dpi; a 40″ diagonal screen gives displays about 54dpi and the whopping 80 incher comes in at 35dpi. What a shocker and that’s HD! The numbers are all approximate because TVs don’t necessarily display all the pixels (hence the “safe areas” in Premiere).
TVs uses various smoothing tricks to make the picture look better than these numbers might indicate. But then, too, viewers don’t usually sit a foot away from an 80″ screen. All that said, what’s the bottom line?
My personal experience is that a 3 to 5 megapixel photo scales nicely in Premiere. If you give it a 50 megapixel photo, it sometimes coughs up a hairball.
But wait, there’s more. Close-up photos with few details look better on screen than long views filled with fine details. I have also noticed, especially when you edit in HDV, but reproduce on a standard DVD, that making the photo move slightly improves its appearance. I often have the photo “swell” about 10% or move a small amount. This seems to result in cleaner edges.
That’s it for now,