Prepping Graphics for Print in Photoshop

Preparing images for the screen is a snap compared to what you have to go through to get images ripe for the printing process. If all you ever want to do is print your images to a desktop laser or inkjet printer, the task is a little easier, but you still must take some guidelines into account. And prepping your images for offset printing? Well, throw in an additional set of guidelines. It’s not rocket science, mind you. If you stick to the basic rules and, more importantly, spend some time developing a good working relationship with your service bureau and offset printer, you’ll be good to go.

Getting the Right Resolution, Mode, and Format
If you’re not familiar with the concept of resolution, I suggest taking a look at Book II, Chapter 1. That’s where I cover all the basics on resolution, pixel dimension, resampling, and other related topics.

Screen frequencies
For the appropriate resolution for color separations in Table 2-1, I list the amount of 2 x the lines per inch. The lines per inch, or lpi, pertains to the screen frequency of the output device. Screen frequencies are measured in lines per inch in a halftone screen. You will also hear the terms screen ruling or line screen. When images are digitized, they are converted into a series of dots called halftones. When you print your halftone, you print it by using a halftone screen of a certain value. The average screen frequency for printing four-color images is 133 to 175 lpi. Therefore, when you multiply that by 2, you need to create your images by using a resolution setting of 266 to 350 dots per inch (dpi).

File formats
As far as file formats go, what you choose depends on a couple of issues:
- What you intend to do with the image. Print it from Photoshop? Post it on the Web?
Import it into InDesign?
- What your service bureau, offset printer, client, director, or other interested parties prefer.