Is there a program which checks the resolution of an image (not including photoshop)

G

GAIL

New Member
Hi

I am currently checking the resolution of images in Photoshop to make sure they can be printed on large wall sizes of 5m and 6m. I have always been told that for print images at 300 dpi have a great resolution. Recently when printing a banner with a 9ft drop the resolution was 9dpi. The printer sent me a test sample and it was perfect. The image size was huge and contained a large number of pixels but I always have that moment of panic when a tight deadline hits and the job needs signed off and I have lots of images to check.

I am looking to see if there is anything on the market which can tell me the maximum size I can use an images at? (or tell me instantly if what I have been sent through is not usable beyond a certain size.)

Thank you in advance.
 
Resolution depends both on viewing distance and printing method. For litho print images do need to be at a resolution of 300 pixels per inch in Photoshop - pixels are digital. DPI (dots per inch) is the laser print resolution. Photos on a computer cannot be called 300dpi - it doesn't exist!!

LINES per inch (LPI) is the term for resolution inherent in the offset printing industry. It comes from when they actually used lines to make up pictures. Modern technology uses dots (or with stochastic printing a more of a “random” pattern in “specs” of ink) and the LPI is determined by the printer.

For large format you have another set of rules - based on viewling distance and print method and I would contact whoever is producing the final work and go by their guidelines.

But no doubt Craig Hudson will be along to give you his words of wisdom!
 
Further to this the 300 ppi/dpi is a myth - there's actually a good comparison here on the usage The Print Guide: LPI/DPI

300 ppi is a rounded off figure.

Each CMYK colour is rotated to create half-tone pattern. The Print Guide: Halftone screen angles


When an image is "RIP"ed it is done so on LPI - the higher the LPI the finer looking the print.


When you take 1 pixel square and rotate it 45 degrees it is basically a diamond shape so from tip to tip on it's side it's 1.4111^ in length (or 1.5 for easier calculations)


It's this number that's multiplied by the LPI to get the appropriate DPI for print.


For example

Newspapers
LPI of 80 up to 120
80 x 1.5 = 120 dpi
120 x 1.5 = 180 dpi

Low end Magazines
LPI of 120-150
120 x 1.5 = DPI
150 x 1.5 = DPI

High End Magazines/Art Books
LPI 150-200
150 x 1.5 = DPI
200 x 1.5 = DPI



The 300 PPI myth basically comes from people taking a LPI of 150 from the RIP which was common in the day - and then multiplying the LPI x 2.

Which is incorrect. But it's certainly not a bad thing.


What most people get back from the printers nowadays is

"Hey your images aren't 300ppi!!!!"

And you just need to ask exactly what LPI their RIP is set to to calculate the minimum DPI you need to set your images at.


Although 300 ppi is a good guess.



As for large banner work

Viewing distance is the key really.

But most large banner work you can get away 30 ppi

But if viewing up closer you may need to up that to 100 or 150ppi.


Hope that helps.
 
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