AI Gigapixel PPI for scanning old prints

(Suzanne Gmirek) #1

I'm scanning a batch of old prints on a Epson V500. I'm having difficulty deciding what is the best PPI to scan at. In the past, I would try and determine what was the largest size photo I wanted and scan for that. It was always difficult to determine what size photo I might want when scanning a bunch of old photos, considering cropping and how bad or good the old print might be.

With AI Gigapixel, I'm wondering if there might be a baseline scan to use and then resize with AI Gigapixel...? Maybe 300 or 600 ppi ....? Does Gigapixel change what I should scan at?

Thanks much for any input,

Suzanne

(Don) #2

GigaPixel doesn't consider what PPI/DPI you scan at as that is a print issue. The only relevant measurement is the pixels width & height as that determines how GigaPixel enlarges the image.

As it isn't a product that resamples based on DPI/PPI just scan at the DPI/PPI you want and that will be rewritten to the output file at the pixel dimensions you select.

(ydobemos) #3

Well, despite not having pixels as such a film print still has grains of ink that form the image. From a certain resolution they would become apparent instead of the image elements and probably wouldn't help the enlarging process.

So the aim is to get as many usable pixels as possible.

According to this article the "resolution" of a 35mm film is about 4000 DPI. I see your scanner should be capable of about twice that. So if you go beyond 400 you would probably get visible grain particles. Sounds to me like you would need to scan close to the given 4000, see if there's visible grain and if there is go lower and lower until you get a relatively clean image (as it may depend on the film quite a bit).

Edit: I sort-of overlooked "prints" and talked mostly about film scanning, but the same rules apply, just, way lower DPI, like Artisan-West said below. In theory 300 dpi is assumed to be the limit of human vision, but if the print is of high quality it might have more (not likely I guess). But the approach would be the same - start high and go ever lower until you no longer see a pattern of dots.

(Artisan-West) #4

Since you are scanning prints, you didn't mention their size. Going by ydobemos's info of 4000 dpi for 35 mm film you would have about 5200 dots on the long side of the film. A 4" x 6" print would then spread 5200 dots over a 6 inch length or be 866 dots per inch of the print (in a perfect printing process). So I would scan at this or less as you would not get any further resolution from a higher scan and just make the file harder to handle in processing. Probably 600 dpi would be fine.

(Suzanne Gmirek) #5

Thank you all for your comments. The article was excellent and I have bookmarked it. I'm starting to understand more about the scanning. I want to get the best scan I can and then if I need to go larger, use gigapixel. I think it's probably better to get as much information as I can from the scan.

Thanks again... you are appreciated :slight_smile:

Suzanne