4 Replies Latest reply on Nov 7, 2012 10:42 AM by johngordon12

# Quick question about Actual and Effective PPI

Hi there - sorry if this is a bit 101, but y background is web design, not print.

A client of mine also produces a printed guide, and I've been helping out the person liasing with the printer as best I can wth questions about file types, resolution etc.

My understanding after a quick look on Google is that Actual PPI is when an image is scaled at 100%, and Effective PPI is the resolution when it is scaled down, ie as the physical size of the printed imaged is reduced, the PPI value effectively increases.

What I hadn't come across before was PPI expressed with two figures, eg 414 x 398 PPI.

What is this in reference to? My best guess at the minute is that they are the Actual and Effective PPIs expressed together - is that right? And if so, which is which?

Thank you!

• ###### 1. Re: Quick question about Actual and Effective PPI

What I hadn't come across before was PPI expressed with two figures, eg 414 x 398 PPI.

No:  When that happens its because the image has been scaled disproportionatly

G

• ###### 2. Re: Quick question about Actual and Effective PPI

Thank you - so for example an image that 600x400px resized to, say, 350x180px? (or more likely actual print dimensions) Resulting in a different PPI value on the x axis to that on the y axis?

• ###### 3. Re: Quick question about Actual and Effective PPI

yes: Correct.

ie: if a square image of 300 x 300 mm is 300 is 300 ppi and it is resized to 400 x 400 the actual ppi is 300 but the effective ppi will drop. The opposit is also true: (resized to 200 x 200 mm the actual ppi is 300 but the effective ppi will increase. but if it is scaled to 200 x 400 then you will find the effective ppi value as such (higher than 300 X less than 300)

G

• ###### 4. Re: Quick question about Actual and Effective PPI

Thank you - it makes sense of course that the vertical and horizontal PPI values could be different, I'd just never seen both figures expressed together before.