# How to determine maximum print size?



## Markw (Aug 24, 2012)

This is going to make me look incredibly unprofessional and unknowledgeable.  :er:

Hey everyone!  Well, long story short, I've got a series of photos seen here.  I've been asked if I could print one of them as 20x30" aluminyzed wall print.  The only thing is, I think it's rather small to be blown up to that size.  I simply don't know, though.  The majority of my non-film work is either used digitally, or has always been printed under 16x24" with no problems.  

So, my question to you all is, what should I look for in the file to ensure it will hold up to a 20x30 size?  Resolution/DPI?

Thanks,
Mark


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## tirediron (Aug 25, 2012)

If you want to determine maximum print size, grab the manual that came  with your printer and see what the largest piece of paper it will handle is! 



The key factor in determining how large a print should (or can) be is the viewing distance.  There was a period not all that long ago when billboard images were being shot with <10Mp cameras.  What you need to find out from the customer is where they're going to put it, and about what the typical viewing distance is.  A quick Google will give you a whole series of formulae and guidelines for size/viewing-distance.

The factors in the quality of of the print are first and foremost, image resolution; the higher the resolution, the more information the printer has to work with.  "DPI" is "dots per inch" or, how many tiny little drops of ink the printer lays down in 1" of travel.  It's important since a higher quality printer will generally lay down more smaller drops resulting in a better rendering of whatever information it is fed.

In summary:  Yes, you can print your files 20x30, but you need to know how close people will be when viewing them to determine if the quality will be sufficient.  FWIW, and 10+Mp camera should turn out a decent 20x30 for viewing at normal distances.


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## Markw (Aug 25, 2012)

Wonderful.  Thanks for that very informative reply.  That thought about the billboard ran through my brain a few times as well.  I was just worried because it was quite an expensive print and I wanted to be able to deliver properly.

So, thank you very much.  I'll report back how the print turns out.

Mark


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## KmH (Aug 25, 2012)

Hopefully, you have a color managed work flow. (see below)

Are you saying the image will be printed on aluminum? If so it will be an inkjet print rather than a chromogenic print and the ink/dye used will be UV-cured.
If the print is going to be on metallic paper it will likely be a chromogenic print, which light sensitive paper having a 3 layer CMY emulsion that gets developed chemically.

Print size is determined to 2 sets of numbers - the pixel dimensions of the image to be printed, and the pixels per inch (PPI) assigned to the image.

Assume you have a photo that has pixel dimensions of 2000 x 3000 pixels. Printed at 100 PPI the print will be 20" x 30" (*2000 px divided by 100 PPI = 20 inches* (the pixel units cancel))
That same 2000 x 3000 px photo assigned to be printed at 200 PPI will be a 10" x 15" print. (*2000 px divided by 200 PPI = 10 inches*)

The more PPI that can be assigned the denser the pixels are in the print, and generally the better the print quality. Many labs set a minimum PPI that they will accept, since their reputation is tiied to the quality of the prints they produce. that limit is usually right around 100 PPI.

If you want to assign more PPI, but the pixel dimensions are limiting the print size, you have to increase the pixel dimensions (up-res) of the image by re-interpolating the pixels. Re-interpolating to up-res means making new pixels that didn't exist in the original photo.

There are several interpolation algorithms available in image editing applications - Nearest Neighbor, Bilinear, Bicubic, Bicubic Smoother, Bicubic Sharper, Step interpolation are the main ones.

Another consideration is sharpening for print. Prints of images look quite a bit different than they do on a computer screen. Many images can be sharpened more for print than they can for electronic display. When sharpened for print, images often look kind of 'crispy' on a computer display.
many image editing application s have a provision for 'soft-proofing' prints on your computer display. Soft-proofing shows on the computer display, a good approximation of what the print will look like. Soft-proofing requires downloading the print devices ICC profile for use by the soft-proofing feature.

Tutorials on Color Management & Printing


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