November 5, 2018
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Creating digital files for digital printing is very much like creating digital files that are going to be displayed on a monitor as a web page or a PDF or JPG – with a few very important differences. In order to help ensure the highest quality of your printed materials, we’re writing this article to offer a useful set of practices for you to follow, from how to set your color space, to bleeds, to resolution. And because we always feel that if people know the why of something the how of it makes more sense, we’re including a little bit of not-too-technological background.
We also have Tip Sheets available on all of these topics: color conversion, file resolution, bleeds, and how to set up your digital files in various programs. You can find them all on the Printing Tips page of our website.
On screen colors add up, on paper colors subtract. What does that mean and why does it matter to you?
Any screen you look at – your computer, tablet, or smartphone – displays color in using the primary colors of light: Red, Green and Blue pixels. We know this as RGB color. On a screen red, green and blue pixels add together to create the entire spectrum of colors that you see. That’s why it’s called additive color.
Color printed on paper uses the primary colors of pigments, cyan, magenta, and yellow (CMY). These pigments actually subtract – or absorb – different wavelengths of light, which is why it’s called subtractive color. So in a sense, yellow isn’t really yellow; it’s the color you see when the pigment absorbs all other wavelengths.
There is a lot of color in the world that you can see, but that cannot be reproduced on your computer, or on a digital printing press. How come? Because color is defined – or described – differently by different devices. How colors are described is called the color space, and that space defines how many colors can be displayed in the case of a screen, or printed in the case of a color printer, copier, or digital press. Your computer describes color in the RGB space (there are several variants, such as sRGB). A digital printing press describes color in the CMYK space.
Not all color spaces are created equal in terms of the total amount of hues they can reproduce. In the case of CYMK, or printed colors, there’s a complicated reason for this, called hue error. To keep it simple, the ink pigments for cyan, magenta, and yellow simply cannot reproduce as many colors as RGB. In a gamut chart, the comparison between the two looks like this.
A digital printing press uses the three subtractive primaries plus black, indicated by a K – or CMYK. Since you view your work in RGB on a monitor, you may notice differences between the colors you see on your computer and the final printed colors. (InDesign and other programs will alert you with an “out of gamut” sign that lets you know you might want to pick a different color that will reproduce better in CMYK.)
Next we’ll talk about best practices for saving your files to achieve the best digital print results.
Photos or Artwork Created in Photoshop
Your photographs from digital cameras and your scanned photos are RGB, the native language of digital cameras, scanners. Digital printing presses print in CMYK. So if you are editing your photos in Photoshop (or another image editing program), or you are creating gradations or artwork in Photoshop, save them in CMYK. IN Photoshop, this is done in the Image/Mode dialog box. Simply select CMYK. You will get a warning box that says, “You are about to convert to CMYK using the “U.S. Sheetfed Coated v2” profile (or whatever profile has been selected for this file).
If you’re a color geek, you can change this profile in Color Settings. However, for printing purposes it won’t matter which profile, because when you save your file you’ll notice an option down at the bottom of your Save As Dialog Box to embed your color profile. Usually this box is checked. Uncheck it before saving. That will turn off any color management files. The reason for this is that the digital press has its own specific color profile, which we will manage for you.
Files Created in InDesign
If you are producing your final document in InDesign, but importing photos and artwork from Photoshop (or other programs) you can save a lot of time by letting InDesign convert the entire file – including all components – to CMYK when you export. This means that you don’t have to spend time converting each photo or artwork to CMYK first before importing. InDesign uses the same conversion engine that Photoshop does, so there is no loss of quality.
Rules of Thumb for Using Spot Colors
Three quick rules apply here. Use Pantone C for the most accurate color match, but avoid using spot colors in conjunction with transparency. Also, use spot colors at 100% rather than creating a tint of a spot color. If you want a lighter color choose a lighter spot color. This will print much more accurately.
If in Doubt, Let Us Do the Color Conversion
Color issues can be confusing, and if you see your job as designing, not defining color space, rely on your friendly Rhino technician to do your color conversion for your RGB document.
We’re digital printing experts serving the Portland, Oregon area and the U.S. For more information, check out our website at: https://www.rhinodigital.com. Or better yet, give us a call at: 503-233-2477. We’ll be happy to answer all your questions and help you with tips and information on getting your printing projects done in the most economical and timely manner possible.