Image Resolution for Photos

Image Resolution and Photo Printing

I don’t really recall when it became popular to have photographic wallpaper in your house. I think it was the mid-nineteen seventies. One day your family room—or the sanctified “den” if you were the type—would be stripped of its last shred of dignity and plastered with an autumn farmhouse scene in red, yellow and orange to compliment the brown shag carpet and the avocado sofa. 

Or a verdant pine forest and the merest glimpse of a distant mountain. Or an aspirational sunset. 

The teenagers had their own version, not full on wall paper, but the teen heart-throb posters of boys with feathered hair, the more than provocative images of Farrah Fawcett or Bo Derek (I swear it was always those two, at least for the time period that I am thinking of). We also had posters that said “Hang in there, baby” with an image of a kitten clinging to a branch.

“That would make a great poster!” Was high-praise for a photo. I started my own journey in photography with a Canon Canonet G-III QL17. It was a viewfinder camera where a yellow image was overlapped with the actual image and when they meshed, the image was in focus. Or I’m confusing that with my Mamiya 7ii. I had many an image I thought would make a great poster, but the cost and the required technology made such a thing pretty out-of-reach. I took no portraits of Farrah, or Chris Atkins; my potential posters tended to be of plants and family members.  I did what everyone does.  I took my photos and put some in an album, and most in a box, and none really got special treatment. 

To Make A Poster

Today, however, there is a way to give photos serious special treatment: large format printers. Because large format printers are designed to print up to 42”, a poster is not only possible but dead simple to do.  No special photographic lab, no mailing negatives to a service bureau.  Just bring the scans to Betts and we’ll print your own Farrah Fawcett. 

Speaking of your personal Farrah,  if you’re looking for wedding invitations, we’re not going to use this technology, it would be cost prohibitive and we have other things like letterpress wedding invitations to offer. (That being said, it might be funny to saddle your family and wedding guests with a poster sized archival inkjet (giclée print) reproduction of you and your happy fiancé.)

A large format printer is a color printer on steroids. It can handle giant rolls of paper and canvas, as well as single sheets of paper (though hand fed) and uses very advanced nozzles to spray carefully controlled combinations of Cyan, Yellow, Magenta and Black (CYMK, see elsewhere) to produce a very fine image.

It can also print out stunning reproductions of your artwork, but this article is about photos not about producing archival-quality art prints or giclée fine art prints of your drawings and paintings.  We do scan and print those as well, and we can even put them on canvas. There’s another article about that. 

Film is made of crystals of silver halide suspended in gelatin. When light hits the silver the grains develop, more light, more development.  These are the black areas of a negative. The kind of film (speed, make and model), the shooting conditions, the type of developer used, all can impact the density of the grains of silver halide. Even the temperature and time of development have their say in how the negative comes out. Color images are even more sensitive as they have a narrower range of temperatures and a more limited diversity of developers. Because film is made of grains, from .2 to 2 microns in size for black and white and up to 25 microns (including the dye clouds) in color, scanning will reveal the grains.

You can think of the grains as a sort of chemical version of pixels on a screen or the spots sprayed by an inkjet. 

How do pixels and dots per inch (dpi) relate to each other?  From the perspective of a scanner, it will take 72 samples each inch when it is set to 72 dpi (the old standard for newspapers). Change the setting to 300 dpi and that’s 300 samples per inch.  The human eye can detect resolution differences in the 300 - 600 dpi. 300 dpi is pretty much the standard for printing.  600 dpi is certainly considered high resolution. 

If you have gotten a scan from your service providers, you can load the scan into Photoshop and look at the image size it will tell you both the dimensions and the dot pitch (dpi). Those dimensions came from the scanner. 

If you want to print out an image at newspaper quality at 20” x 30” the resolution of the file would be 1440 x 2160 pixels. If you want it that size and at photo quality (300 dpi) the size would be 6000x9000 pixels and 12000 x 18000 will be the 600dpi ‘high resolution’ size . It’s the number of pixels that determine how large you can print before the image starts to suffer. You would be able to double the size of the image with the 600 dpi to 40” x 60” and it should have the same resolution as the 300 dpi does at the 20” x 30” size.

I suppose I should take a moment to address the ugly topic of the “best” way to scan a negative for reproduction on a Large Format Printer. There isn’t one best way. Some people use a digital SLR camera (or even the mirrorless cameras) to shoot the negative. Sometimes they stitch those together in a tool like photoshop so they can really get high resolution. Some say drum scanners are the best. Others swear by flatbeds, and of those, some prefer wet over dry. 

Believe me, forums discussing this issue are the most testosterone filled, chest thumping nerd crap you ever laid eyes on. 

Best Resolution Is…

The best way to scan the film is a way that preserves enough information for you to make your final print align with your idea of what would be the best way to present that image. 

Robert Maplethorpe loved strong, contrasty images: blacks are black, whites are sparing but certain. Portrait and still life are very much alive because of a sensitivity to form and movement. 

Edward Weston was very tonal, and while blacks and whites figured in their pure form, the tonal range was a stronger component. His work was organic and undulating, even his egg slicer, but where Maplethorpe grabbed you as a viewer, Weston lays a visual trap that has you before you realize it. 

That’s what I mean about the “idea of what would be the best way to present that image.”

One last matter, ratios.

The kind of film you use will also influence the proportions of your final image. That in turn will determine what picture frames you can buy off the shelf for your image. Always plan for a mat to accommodate your image, and a frame to accommodate the mat (unless you want to be mat-less).

A 35mm negative frame is 24mm x 36mm.  Thats a 2:3 ratio, so it will be a natural to size up to anything that fits that ratio.  No part of the image will be lost. 4”x6” is a common post card size.

Medium format film is 6cm tall by 4.5cm - 9cm. The actual frame size of a 6x6 is 56mm x 56mm, giving it the wonderful but idiosyncratic 1:1 ratio.

Large format film is usually: 4” x 5”, 5” x 7”, 8” x 10” making them ratios of 4:5, 5:7, and 4:5, respectively.

Manipulation

Color correcting, spotting and all sorts of other changes to the digital file can certainly be part of what we do for you, but we’ll respect your digital file as being your final work and do our best to make a faithful print of it at the size you want.