BetterPhoto Q&A
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Photography Question 
Nancy Barnhart


I am scanning wedding negs. and I thought there was a magical dpi and size, like 150dpi at 5 X 7 that would allow for great enlargements without having to scan them all huge to begin with. Is that true?

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8/7/2007 10:54:29 AM

doug Nelson   What size neg are you scanning? I would not go below 2400 pixels per inch scanning resolution for 35mm negs. Do more if your scanner is up to it. Medium format needs at least 1600 ppi, more if you can. An advantage in scanning at high resolution and high bit depth (scanning them huge, if you will) is that you have an image with the max of pixel and color information to squirrel away on a CD of raw files. You can tweak brightness and color, crop and SAVE AS, without destroying your "original". You never know how big an enlargement the customer might want, so you want the resolution to cover that possible need.

Your question about 150 ppi at 5 x 7 seems to refer to a print resolution. For printing, it is safest to go for 300 ppi to input to your printer for the size you want. 300 is a standard industry input resolution. Some printers will let you get away with 240 ppi.

For fun, open one of your full resolution images after the scan. In Photoshop, go to the Image Size screen. Elements has an equivalent screen. UNCHECK Resample. Enter 300 as the resolution, OK it, and let the program calculate the image size for you. If its the size you will want to print, you're good to go. Also, you can enter the max image length (or height) you will need and OK it, and see what the resulting resolution will be. As long as you are not in the Resample mode, you won't be wrecking the image, just reshuffling the pixels. The file size, ie. total number of pixels will remain the same. This, done as I have desribed, only spreads the pxels out or scrunches them up. No pixels are thrown away or created out of nothing.

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8/8/2007 8:32:19 AM

Nancy Barnhart   Thanks for the response. I am scanning 35mm and medium format negs. Looks like 300 is the way to go. The folks I'm scanning for want to be able to enlarge to 8 X 10 and 11 X 14.

Our scanner is an Epson Perfection 2450.

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8/8/2007 3:50:05 PM

doug Nelson   Scan at a scanning resolution that gives you 300 pixels per inch after you scale the image out (in Image Size) to a 14-inch image length.

I set output in my Epson V700 to "original size". I get an image the same size as my negative to play with in Image Size (Resample UNchecked). I scale it out to 10 inches (if that's to be my image length) and see where the resolution falls.

Ask me or someone else if you don't understand this. I had a hard time "getting it".

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8/8/2007 4:45:22 PM

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