Advice on scanning old photos, and what DPI to use?
When you scan and archive your old photograph collection the first thing you need is a decent flatbed scanner. This might be an standalone scanner, or maybe these days in your all-in-one printer with a scanner included. There is no need to buy a new one if you current one still works.
The next thing to understand is what DPI should be used when scanning old photos. The answer depends on the two things:
Let's look first at the quality of the original photo. Basically scanning a blurry photo at more than 300 DPI is a waste of time, memory and disk space. But if you scan a sharp photo at 300 DPI then you are probably losing detail.
A blurred photo does not change much from pixel to pixel, and many pixels will have the same value as surrounding ones.
A sharp photo on the other hand has many changes from pixel to pixel, so to capture them you need a higher scanning resolution compared with a blurred photo.
The problem is how do you tell a blurred photo from a sharp photo? Though there are technical ways of doing it, I always do it by eye. Here is what I consider a blurred photo scanned at 600 DPI and at 300 DPI:
I think you'll agree that there is not much difference. If I was going to print the photo at the size you see it on the screen then 300 DPI would be perfectly adequate. That is what point 2 in the list at the top of this page is about. What is the final use of the photo?
Let's pretend that I really really want to print this embarrasing photo from 1975 on a large A3 sized photo. (A3 is like 4 letter pages put together). If that were the case then differences would appear in the 300 and 600 DPI versions. You can maybe see this in the closeup shown below:
Look at the highlights on the door handle. On the 300 DPI, if you had print the photo very large, you would just be able to see the pixellation. So if you are going to print your scans at larger than the size of your original photos you might want to scan at 600 DPI even if they are a bit blurred.
Now if your photos are pretty sharp to the eye it may well be worth scanning and saving them at 600 DPI. In the example below you can see that the tower (Cabot Tower in Bristol, UK) is definitely more pixellated at 300 DPI than at 600:
And if you intend to print this at larger than the original size it you definitely need to scan at 600 DPI.
If you use RansenScan (which scans and separates multiple photos in a single pass) you need to scan at the highest resolution required for the photos on the scanner bed. If they are all blurry and you'll never print at larger than original size then 300 DPI is fine. If even one of them is quite sharp and you want to preserve that sharpness (for future generations) then scan at 600 DPI.
After all, you don't need to be a photo-restoration expert to do this. The newest generation of inexpensive scanners together with RansenScan makes it easy for anyone to scan and correct old photos. V3 of RansenScan even has an Automatic Brightness and Contrast enhancing function:
So dust off those pictures, fire up your scanner and get ready to breathe new life into your old photos!
One thing is clear: No matter how carefully packed or protected, these photos are decaying. There are scratches and tears, and the hues are fading/changing in color photos (the darks are lightening in black and white photos) - and no economically viable preservation efforts in the universe can prevent this. The only way to make sure that historic or personally important photos survive is to scan and digitally restore them, and maybe print them again.
(As an aside: I'm an electronic engineer who writes software, so I should love new technology. But since I'm so closely involved with it I know it's limits. I always print out old photos I want to preserve. Why? Well, the Lascaux cave paintings have lasted thousands of years, how many precious memories have been lost to now unplayable VHS tapes or CDs and hard disks which no longer work? A USB memory stick 've had for 2 years has just become unusable. But I still have my albums of photos.)
RansenScan has a free demo (for all versions of Windows from XP to 8) so you can test the scanning of your own photos at various DPIs: