What resolution should I scan photographs with?

jmk396 wrote on 6/10/2007, 10:46 AM
I'm looking to create a simple photograph slideshow using scanned-in photographs but I don't know what quality or format to use.

These photographs will be displayed full-screen (NTSC resolution which I think is 720x480) and zoomed/panned a little bit.

So... what resolution should I use?

...and which file format should I use? (TGA?)

Finally, does anybody have any tips for making a better looking slideshow? I've seen a few neat effects but I forget most of them.

Thanks!

Comments

Chienworks wrote on 6/10/2007, 12:25 PM
The resolution depends on the physical size of the photo that you want to have fill the screen. If you were going to have a 4x6 picture fill 655x480 (square picture resolution of SD NTSC video) then divide 480 pixels by 4 inches to get 120 pixels per inch (dpi). Most scanners don't have a 120 setting so go to the next higher one, usually 150. It's good to scan a little bit larger than the final result anyway to allow some room for cropping.

Now, lets say you want to be able to zoom in on an image. Maybe you have a family group photo and you want to zoom in on grandma's face, which is about 1/4" high in the photo. 480 pixels divided by 1/4" = 1920 dpi.
jmk396 wrote on 6/10/2007, 1:33 PM
Thanks for the reply!

Most of the pictures I have are 4x6 or smaller so it sounds like 150 DPI would be a good number to use, right?

Also, what do you mean by 655x480 is the "square pixel resolution" of SD NTSC video? I thought NTSC video as 720x480. Which resolution should I be saving this video as? (655x480 or 720x480?)
rmack350 wrote on 6/10/2007, 2:47 PM
It's more complex than that. Usually, DV is described as using non-square pixels. The upshot of that for stills is that, in NTSC, a still exported by Vegas from DV footage would be corrected to 655x480 (actually rounded up from 654.54... by 480)

So, you need to allow for this. A 655x480 still imported to an NTSC project in Vegas will look "right". Perfect circles and squares will remain perfect. Vegas deals with this automatically.

This is common to all NLEs. Don't worry to much about it.

As a side note, since vegas is rounding these dimensions to the nearest whole number, you could choose a still image size that is already a whole number. For NTSC, 720x528 works perfectly, and Vegas actually keeps every one of those 720 pixels. If you have very fine vertical details this will preserve a tiny bit more of it.

Rob Mack
Laurence wrote on 6/11/2007, 7:36 PM
Don't forget that if you're doing pans and zooms you need more resolution. I usually use 1440 x whatever for SD so that I can zoom into a quarter frame without interpolation. For HDV I use twice that (2880 pixels accross).
Chienworks wrote on 6/11/2007, 8:40 PM
Remember that the square-pixel resolution for HD / HDV is 1920x1080, not 1440x1080. So you should be scanning based on 1920, not 1440.
Laurence wrote on 6/11/2007, 10:04 PM
With interlaced 1080i HDV, the vertical resolution is really only 540 rather than 1080 lines. Because of this I feel pretty good importing a 1440x810 square pixel image into a 1080i HDV project if I'm not zooming in at all. 1920x1080 certainly won't hurt, but I personally use 1440x810 as a minimum for HDV and can't see any loss at those dimensions no matter how hard I squint.

2880 x whatever (since there is usually extra hight in a photo) allows extra resolution for up to quarter frame zooms. I would use 3840 horizontal pixels for zooming into a progressive image though.
Chienworks wrote on 6/12/2007, 2:50 AM
Each field is only 540 lines, but the two fields together make up a frame that is 1080.
Laurence wrote on 6/12/2007, 7:51 AM
Yeah but all the new HDTVs are progressive (I have an old interlaced CRT HDTV but that is not the way it's done anymore). When the two 540 line fields of 1080i content are displayed, I believe that current 1080p HDTVs show one 540 field every sixtieth of a second and interpolate it up to 1080 lines. I might be wrong but I'm pretty sure that this is how it's done.