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Avoid printing problems with proper preparation

Added on Saturday 26th of March 2005 11:54 pm EST
 

Application:

Adobe Photoshop 7/CS

Operating Systems:

Macintosh, Microsoft Windows

Keywords:

Photoshop, CMYK, Printing, Resolution

                

Preparing your Photoshop documents for professional printing can be a hassle, especially when you have to worry about color modes, profiles, and resolution. Once you have a basic grasp of these issues, you can then apply that knowledge to your files before sending them off to a printer.

 

To help you better understand the details of the printing process, we’ll:

       Decipher the relationship between resolution and image size so your images are suitable for your output device.

       Map out proper color settings to ensure your files separate and print correctly.

       Explain the main file formats most widely supported by the printing industry.

                

Typically, designers create their images in Photoshop, and then use a program like Adobe InDesign to prepare their layouts for print. There are many considerations you must make when creating files that can drastically affect the success of your print job down the road. Let’s take a look at what factors you should consider to ensure you make the right choices when creating your support files.

 

Resolution

Monitors and printers measure the resolution of an image differently. To calculate what your image resolution needs are, it’s important to understand the lingo as well as image size.

 

Learning the lingo

The term dots per inch (dpi) gets used more frequently than it should. Since that claim to fame belongs strictly to your printer, let’s clarify the more commonly used resolution terms.

            Image or monitor resolution (ppi). This is actually the display resolution. Your monitor displays everything in units referred to as pixels per inch (ppi), which are square in shape. The average computer monitor displays images at a resolution of 72 ppi.

            Printer resolution (dpi). Your Photoshop image doesn’t turn into dots until it’s printed. A dpi value represents the quantity of halftone dots per inch (dpi) a printing device can produce.

            Scanner resolution (spi). When a scanner makes a pass, it takes samples from the image. Your scanning software enables you to change the samples per inch (spi) settings. Keep in mind that even scanner manufacturers misuse the term dpi—often labeling the scanning resolution as dpi instead of spi.

            Halftone resolution (lpi). The number of lines per inch (lpi) a device can output determines the number of halftone dots in a 1-inch-square grid. These halftone dots are what create the illusion of tonal range, as shown in Figure A. Line screen is determined by the output device and the type of paper being used for printing.

 

.

A

                

Image size

The image size is the actual pixel dimension of your image. You can check or modify the size of your image using the Image Size dialog box shown in Figure B. To access it, select Image > Image Size.

 

B

 

In the Image Size dialog box, you can modify the size of your image’s Width, Height, or Resolution by entering the desired values.

            Scale Styles (CS only). If you select this check box, layer styles you’ve applied to your image will scale along with the image. If it’s deselected, they won’t.

            Constrain Proportions. If you select this check box, the Width and Height values remain linked, so the proportions of the image remain consistent.

            Resample Image. This check box controls how changes made in this dialog box affect the image’s resolution. If you deselect this check box, the size of the image remains linked to its resolution. For example, before cropping, your 150 ppi image might be 8 inches by 8 inches. After adjusting the resolution to 300 ppi, the image would shrink to 4 inches by 4 inches. If you select this check box, Photoshop will add or remove pixels when changes are made.

 

              

Caution: Resampling is okay if you’re making the image smaller (though you may want to save the result as a copy so you don’t lose the higher-quality original). If you use resampling to make an image larger, however, Photoshop creates new pixels by guessing with the aid of mathematical algorithms. This can work for minor enlargements, but in general the larger you go, the lower the quality of the finished image. You’re better off starting with a high-resolution image.

              

 

Calculate your resolution

An image for the web only needs to be 72 dpi, whereas the resolution requirements for print images vary. Generally speaking, you want your image to be twice the linescreen value. An average linescreen is 150 lpi, which would put the image resolution at 300 ppi. In addition, some high-speed presses impose limitations on the maximum resolution of your image. Consult your printer for specific recommendations about the linescreen and the press they’ll use to print your files.

 

              

Paper stock

The paper you’re using also influences the resolution needs of your image. Paper tends to absorb ink that’s applied to it, which causes halftone dots to spread and become larger after the ink is added. Printers call this effect dot gain. Thus, the more porous the paper is, the greater the dot gain, limiting the quality of the finished image. Paper with lesser dot gain can emulate higher detailed images. Three common types of paper are:

            Newsprint. Requires an image resolution of 85–100 ppi.

            Uncoated paper. Requires an image resolution of 266–300 ppi.

            Coated paper. Requires an image resolution of 300 ppi or more.