THINGS TO CONSIDER WHEN OVERPRINTING BLACK INK The CMYK color mode is the color mode of paper and press. Printing presses (sometimes referred to as a 4-color press) convert an image’s colors into percentages of CMYK (Cyan, Magenta, Yellow, and Black), which eventually become the color plates on the press. One at a time, the plates apply color to a sheet of paper, and when all 4 colors have been applied, the paper contains an image similar to the CMYK image created in Photoshop. The CMYK color mode can take an image from a computer monitor to a printed document. Before converting an image into the CMYK mode, however, it’s important to understand that you will lose some color saturation during the conversion. The colors that will not print are defined as being out of gamut. To view the areas of an RGB image that will lose saturation values, click the View menu, and then click Gamut Warning. Photoshop will mask all the areas of the image that are out of gamut.
You have probably heard or read that process inks are transparent: that when process inks are laid over one another, they act as filters (somewhat like gelatin filters on theatrical spotlights) to subtract certain wavelengths of light and reflect other colors. This is the nature of process color printing.
However, it's important to remember that not only cyan, magenta, and yellow inks are transparent. Black ink is transparent, too.
When is this important to remember? When you're overprinting a process color image with black ink. For instance, if you print a portion of a large initial capital letter over a 4-color photo, with a portion of the letterform extending beyond the boundary of the image onto the white paper surrounding it, the black ink overprinting the photo will look different from the black ink printed directly on the white paper. In effect, you will see the cyan, magenta, and yellow of the photo through the transparent black process ink.
One way to fix this problem is to use a rich black (a combination of process black ink with an additional percentage of magenta and cyan). Different commercial printers will have their own mixtures (ranging around a 50 percent magenta and/or cyan ink limit), and these rich blacks will be either cooler (more cyan) or warmer (more magenta).
In addition to providing thicker, richer ink coverage than process color by itself (i.e., 100% black plus 60% cyan, plus 40% magenta for a total of 200% ink coverage plus any yellow (40%)—as opposed to just 100% black), rich black ink will overprint 4-color process images (or process color screens) without creating a distinction between where they overprint the image and where they overprint the surrounding white paper. (If you specify a rich black in your InDesign file, do check the printer's proof carefully for any color problems.) Another solution would be to manually knock out the 4-color image below any type that would otherwise cover both the photo and the surrounding white paper. To go back to the example above, most print layout applications would print black type over the photo without deleting the image below the type letterform. (This would only be true for black ink. If the overprinting type letterform were any color but 100% black, most page layout applications would knock out the 4-color inks below the overprint.) One can override the default on most if not all layout programs to disallow the printing of black over process colors. In this case, the 100% black letter would print directly on the white paper, whether it is within the boundaries of the 4-color image or outside its perimeter. The portion of the photo beneath the letterform simply would not print. (As long as it is printing process colors on a 4-color press, either of these solutions would cost the same; however, it would still be wise to discuss your options with CSP).
Rich black is an ink mixture of solid black, 100% K, with additional CMY ink values. This results in a darker tone than black ink alone. If you print black alone as 100% K, the resulting black may not be as dark as you might like.
We recommend using
C 60 M 40 Y 40 K 100
This will give you a deep, dark, rich black.
CMYK vs RGB
Working together with web and print designs can be tricky and learning how color works can be the key to getting a successful color calibration for both your website and your printed designs such as business cards and brochures.
Web design uses color as RGB (red, green, blue) and print design uses color as CMYK (cyan, magenta, yellow, black.) Basically, monitors emit light and papers absorb light. Computer monitors show color as red, green and blue light at a low-medium resolution usually 72-75 dots per inch.
Print production usually requires the four-color process CMYK in high resolution of at least 300 dpi.
Although all colors can be achieved by merging red, green and blue light, monitors are capable of displaying only a limited range of the visible spectrum. So when you want to convert your web files to produce artwork for business cards or brochures, changing the format from RGB to CMYK is very important for those printed documents. If you are using Adobe Photoshop select: Menu> Image> Mode> CMYK when you begin a new file.
When CSP receives RGB files we will automatically convert the images to CMYK however that can result in faded, dull or inaccurate color representation in the final project. Converting your file to CMYK gives you better control over the final image outcome.