Digital to Photographic paper (TIP)

[Ron]

I have an old family photo that I want to touchup and get printed at a photoshop on regular photographic paper.
I've found lots of advice on what resolution to scan pictures if I want to put them on the web or print them on my home printer. In fact the best advice I found was by member Shan Canfield at http://www.shanzcan.com/photoshopahol.html
(see her work on Retouch Challenge #2 http://www.retouchpro.com/challenge/..._canfield.html).
As useful as Shan's information was however, it still didn't tell me what scanning resolution to use to make prints on photographic paper. Recently however, I found the information I was looking for at 'Shutterfly', a web site for storing and sharing online photos. This site is like Webshots and one of the services it provides is making regular photographic prints from digital images. http://www.shutterfly.com/index.jsp
(By the way; because of increasing digital cameras use, there are a number of 1 hr photoshops setting up to print digital pictures -- they usually will require jpeg format --).

On one of Shutterfly's help pages (under ordering prints) I found the following information about the ppi resolution requirements for getting prints made.

1) less than 480 x 640 - Only wallet-size prints recommended
2) 480 x 640 - Absolute minimum resolution for 4x6 prints (results will vary)
3) 768 x 1024 - Recommended minimum resolution for 4x6
4) 864 x 1152 - Recommended minimum resolution for 5x7
5) 1200 x 1600 - Recommended minimum resolution for 8x10

They also recommend that you use the least jpeg compression possible. While high resolution and low compression increase file size, they produce the best results.

As a guideline, these ppi measurements make it easy to establish the resolution to scan any image you want to make a photographic print from. Just take the ppi measurement and divide it by the size of the print in inches and scan at the higher ppi figure.

For example a 4x6 print --
768/4 = a scan resolution of 192 ppi
1024/6 = a scan resolution of 171 ppi
Therefore you'd want to scan at 192 ppi but I'd bump that up to 200 ppi…

On the other hand, if you want to start with a 4x6 print and then enlarge that to a final print size of 8x10 you need to scan the 4x6 at a higher resolution. To find the scan resolution required for the enlargement, divide the ppi required for the 8x10 by the starting print size.

For example starting with a 4x6 print -
1200/4 = a scan resolution of 300 ppi
1600/6 = a scan resolution of 267 ppi
Therefore you'd want to scan the 4x6 print at 300 ppi so that the final 8x10 enlargement would be of sufficient quality.


Ron

[Ed_L]

Ron,

Thanks for posting that information. It should help people get in the ball park. I think some print makers might have different preferred resolutions, but the numbers you provided should be a good starting point. Thanks again.

Ed

[DJ Dubovsky]

Great tip Ron. One that really takes the mystery out of the big question "what size do I scan at?" I know alot of people like me will make valuable use out of this tip.
DJ

[Ron]

Originally I started this post so others could learn from my mistakes. A while back I wanted to work on a family photo and have it printed on photographic paper (so I could send the prints to other members of my family). All the advice I could find told me to scan at as high a resolution as possible. I therefore scanned my 5x7 image in at 1200 ppi and ended up with a 47MB psd file. A couple of layers and repairs latter this file had mushroomed to a whopping 238MB.

More research led me to the "Shutterfly" web site where they told you exactly what the minimum resolution should be. (see above).

Since then I came across another site "Ofoto", which specifies that their prints have the same archival quality as prints made from 35 mm film. Surprisingly their minimum specifications are a full stage lower than "Shutterfly"
4 x 6 print = 480 x 640 pixels or 120 ppi
5 x 7 print = 768 x 1024 pixels or 154 ppi
8 x 10 print = 1024 x 1536 pixels or 153 ppi

A more definitive web site I came across recently tends to verify these extremely low "pixel per inch" image values and explains why these figures are so low. Check the full article out at http://www.scantips.com/basics08.html

It appears that a 5 x 7 print made from a 35 mm negative can only contain a specific amount of detail. The amount of detail that is available in a print is dependent on the inherent qualities of photographic paper. Scanning images "from" photographic paper achieves its maximum amount of detail at a value less than 300 ppi. [The detail in a B&W print might be stretched to 400 ppi]. Scanning at higher levels doesn't provide any more detail because its just not there.

An 8 x10 enlargement made from a 4 x 6 print can never be as sharp or as detailed as the original (it'll just be bigger) and scanning at higher values than 300 - 400 ppi will not help.
If you want a quality enlargement you have to return to the negative, which does have the detail capacity to increase the size of the print.

In conclusion, don't fill your disk up with bloated scan files that are just a waste of space, like I did.

Ron

[DJ Dubovsky]

Ron
Again, very informative and helpful to all of us. Thank you for taking the time to help simplify this for us. I had that web page but I actually think you did a better job of laying it out for us.
DJ

[Sally]

Scan size and output. I output all my prints to Pegasus photographic paper. I usually scan at 600 dpi because that is the highest that my scanner will do without interpolation. If I start with a large print then I scan at a lower resolution, say an 8” x 10” print would be scanned at 400 dpi.

I always output at 250 DPI, that is what the lab uses. I like to have a large file to work with because that allows me to enlarge portions for fine detail. When I’m finished I reduce the file to what is required and sharpen to compensate for the small amount of sharpness lost in re-sizing.

I hope you find this helpful. Contact me if you want more information. Sally Cowell. [email protected]

[Ed_L]

Sally,

Welcome to the site, and thanks for your insight on the above. Yes I think a large file is easier to work on for fine areas since the image doesn't seem so pixelated. Now you have me wishing for a better, and faster computer. I often have problems with very large files.

Ed

[thomasgeorge]

For what this is worth, ( not much probably), I was told that for a 4x5 to an 8x10 size print to scan at twice the line screen.My scanner software allows the line screen to be adjusted and I usually use the 133 setting which is suppost to be good for hi end magazine/art prints. This puts the scan res at around 266, but I scan everything at 300 and so far, it seems to give good results---Just some more semi-coherent ramblings from up north. Tom