Effective and actual ppi?

[_Kelly_Crossley_]

What's the difference between effective and actual ppi? Is there any reason I need to adjust the actual ppi if it's more than 300 x 300 ppi?

[Guest]

"Actual" ppi is the resolution of the image at 100% size, as set in Photoshop.

"Effective" ppi is the resolution of the image at the size it's been scaled to in InDesign.

For example, a 300 ppi image, if scaled 50% in InDesign, is actually 600 ppi when reduced to that size. Make sense?

[hlwaddell]

What can you do if an image has an actual ppi of 300 but an effective ppi of say 115 - 240? At what level will it be safe for commercial printing?

[Peter Spier]

240 effective ppi is probably adequate for almost any commercial printing other than fine art reproduction. 115 could be pushing your luck, but there are so many variables that it's impossible to say anything absolute. What is the intended use and the intended viewing distance? What's the printing method?

You might want to take a look at http://forums.adobe.com/message/2042202#2042202

[hlwaddell]

Thanks, I am using the images for posters for conferences so people can walk right up and look at it in the booth. I have had some luck sourcing higher res images.

[Peter Spier]

Posters for booths are usually printed using inkjet plotters, I think (that's how we used to do it where I worked on my second job in this business), and though you can walk right up to some of them, they really are intended for viewing from some distance away in most cases (but yours might be full of 12 pt type and other stuff that can't be read from more than 18"). For that sort of work, 150 ppi is usually all that's requested, and you can easliy get away with less most of the time.

[Guest]

Oh, and you don't necessarily need to adjust the image if it's more than 300 ppi. There may be reasons to shrink your images in Photoshop (eg. running out of disk space, printer requests it, etc.), but there's generally no need to.

[Guest]

I'd say you might consult with your printer on whether you need to scale the images or not. Some are more picky than others about what the minimum and maximum allowable scaling are for their device.

[_Eric_Otto_]

If you're using a PDF workflow with your printer, your images will be downsampled when you make your PDF anyway.

[_Peter_Truskier_]

>your images will be downsampled when you make your PDF anyway.

Assuming that your export/Distiller settings are set to do so...