Questions for Preparing Digital Images for Printing
Digital cameras may be easy to use, but digital images still need some attention before they're "print-ready" - just like conventional photographs. However, digital image correction at the prepress stage can be costly and add precious hours to already compressed production and mail-drop schedules. To help you prepare digital images properly, here are answers to some of the most common questions we get asked at EU Services:
JPG, GIF, TIFF, EPS ... which are the best types of image files for printing? The simplest way to break down the different types of image files is to classify them as either "lossy" or "lossless" compression files. "Lossy" compression files, such as JPG, GIF and PIC, sacrifice image information for a smaller file size. This makes these file types popular for Web applications that put a premium on size over detail.
"Lossless" image files, such as TIFF and EPS, retain much of their information during compression. This yields a much larger file, but also allows for much higher resolution and much finer control over image details and color.
At what resolution should I save my images for printing? Resolution essentially refers to the amount of information in an image. The higher the resolution, the more detail an image possesses. The "correct" resolution for an image should be based on how it will be displayed or output. Images that will be displayed only on a monitor, such as those on a Web site, require only a resolution of 72 dpi (dots per inch), as that is the maximum resolution a monitor can display.
Images that will be printed professionally require higher resolutions because a printed piece yields much finer detail. Most printers require images to be at least 400 dpi for accurate reproduction while 600 dpi may be preferable for certain high-quality applications. To ensure that digital images contain sufficient resolution, set your camera for the highest resolution (or largest picture or file size) available. Though this may limit the number of images you can store, it will give plenty of color information to work with.
Why is my printer asking whether I performed a "RGB-to-CMYK color conversion?" CMYK refers to the four process colors used for printing - cyan, magenta, yellow and black - while RGB refers to the red, green and blue palette used by monitors to display color. The two are very different in how they formulate and display colors.
If your printer is asking you to perform a color palette conversion, it's likely because the image was created with a digital camera, which saves photos in RGB color for viewing on a monitor. These must be converted to the CMYK color palette for printing, which can be done easily in Adobe Photoshop.
I've heard that duotone images are difficult to create from digital image files. Is this correct? Duotone images - a single spot color added to a black-and-white image to create the illusion of multiple colors - are inherently difficult to reproduce for several reasons. First, the amount and intensity of color added to a black-and-white image to create the duotone is subjective. Simply telling your printer to "add blue highlights," for example, won't guarantee that the resulting duotone will be close to what you have in mind. You may want to provide your printer with a sample of an image that exhibits characteristics you wish to see in yours.
Proofing duotone images also can pose a challenge. Color proofing devices reproduce proofs using the same CMYK color space used in four-color printing. Therefore, the spot color used in your duotone must be approximated using process colors. Proofing duotones on your computer screen can be even more challenging. That's why we recommend either a contract proof or press check for projects that include duotones.
Why are the results so unpredictable when I perform color correction of my images on my computer? Once again we go back to the main difference between how color is rendered on computer screens versus the printing process. Monitors use a different color gamut than what's used for four-color process printing. That can lead to substantial differences in color between the image you viewed on-screen and the image your printer reproduces. The best way to ensure that your printed images have the exact color characteristics you desire is to let your printer handle color correction for you.
If you prefer to perform your own color correction, it's wise to calibrate your monitor to match the color profiles used by your printer, if possible. Remember that high-level monitor-calibration systems are expensive. Also, if you use multiple suppliers for printer work, you may need multiple color profiles to ensure that what you see on-screen will be represented accurately on printed pieces.
Digital images are a boon for busy marketers who need to put campaigns together as quickly as possible. A little attention early in the design process will save you time, money and headaches during production, and yield better results in the mailbox.