At what dpi should I scan pictures for AppleTV? What is best format?

You are scanning at far too high a resolution for TV display.

dpi is pretty irrelevant for outputting to TVs via devices like AppleTV.

HDTVs currently generally max out at 1920x1080 resolution for full HD, so resolution is a better thing to consider than dpi, particularly as AppleTV won't have a clue whether you have a 32"/42"/50"/60" set or whatever. Screen sizes are measure diagonally too.

Even if your TV can handle a full HD input chances are the panel isn't even 1920x1080 res at 32" size (Panasonic have announced one but I'm not sure it's out yet).

If you measure the horizontal width of your TV screen in inches and then divide 1920 by that, you'll get an idea of the max dpi the TV could display if it had a full HD panel.

For simplicity say the TV screen was 20" wide then it would physically have around 96 dpi, but a 32" TV will be wider and dpi lower.

I recommend you aim either to get images of 1920x1080 which is tricky if scanning and cropping, or to have a somewhat higher res to allow for the panning/zooming of Ken Burns effect which only shows a slightly cropped area at a time. Exact amount for Ken Burns won't be much but I can't tell you exasctly what size to make images to display 1:1 pixels. It's probably 20-30% larger buy may be a bit more or less. Frankly even 1920x1080 or smaller images scale fairly well on AppleTV.

So 1200x1200 dpi is certainly overkill for AppleTV, even for home printing much more than 300-600dpi would be overkill for most applications.

What might be best is for you to scan at 600 dpi so you have high res 'original scans' to work with now and to avoid rescanning in the future (unless you're printing much larger than the originals), then to crop and export copies a little unjder or above th 1920x1080 resolution and let AppleTV take care of scaling.

One other thing to remember is that your photos are 3:2 aspect ratio but TVs are 16:9. You could either crop yuor scans before exporting to a 16:9 shape or let AppleTV crop on the fly (it won't distort the shape of photos to fill the screen if they're narrower than 16:9 as far as I can remember).

So in essence I'd suggest scanning at high res for posterity, but to use iPhoto to export to smaller AppleTV friendly sizes.

AC

At 600dpi your 3x2 images would be 1800x1200 before cropping - I suspect good enough.

At 600dpi your 6x4 images would be 3600x2400 which is more than enough for AppleTV and could be scaled down closer to 1920x1080.

dpi is a very artificial concept for an actual image - for a 6x4 600dpi scan it would describe an image resolution suitable for outputting a 6x4 image at 600dpi, whereas yuo hardly want your 6x4 displayed at that size on a 32" set!

Best to ignore dpi and just think in terms of resolution.

I'd also add that office scanners can do pretty good photo scans but will not be in thesame league as negative or professional photo scanners, and much of the 'high resolution' options may be derived by software interpolation once the scanner's actual optical acuity is reached.

AC

Does the dpi correlate to HD resolution?

As others have already indicated, the answer is "no." Consider the scans in terms of density (dpi) when your goal is printing the content. Consider the scans in terms of size dimensions (resolution) when your goal is to display them on a monitor or screen. Best advice here is to scan them at the greatest density and size you would normally use. As far as the TV is concerned, anything over 1080x720 (3:2 landscape), 480x720 (3:2 portrait), 960x720 (4:3 landscape), 540x720 (4:3 portrait), or similar size/aspect combinations are probably a waste of storage space unless you plan to use them for other purposes (or have a true 1080p rated HDTV). Anything else will be scaled up or down as required depending on your TV/HDTV settings.