The Photoshop Tip of the Week for the Clients and Friends of Ben Willmore (www.digitalmastery.com):

A couple of weeks ago, we looked at tips related to web graphics. This week, lets dive into the ink and talk about images destined for a printing press.

Whenever an image is reproduced on a printing press, it needs to be converted to CMYK mode before being output (unless you’re using spot colors, that is). I prefer to work in RGB mode for as long as possible before converting to CMYK. Here’s why:

5 GREAT REASONS FOR WORKING IN RGB MODE

-Dozens of filters are grayed out in CMYK mode, but are available in RGB mode.

-Many filters produce a better result in RGB mode (like the Emboss filter).

-File sizes are 1/4 smaller.

-Any color fading to black will look better if created in RGB mode, and converted to CMYK later.

-When working in RGB mode, you don’t have to commit to a particular type of printing until the image is converted to CMYK.

Having said all that, let’s look at some techniques that are specific to CMYK mode.

After sharpening the overall image, you can sharpen the Black channel to bring out extra detail. To do this, clicking on the Black channel in the Channels palette, apply the Unsharp Mask filter, and then click on the top-most channel to get back to the full color image.

To increase the amount of detail in a green area, increase the contrast of the Magenta channel—for a red object, work on the Cyan channel and for a blue object, work on the Yellow channel.

To make a red object appear redder, reduce the amount of cyan using Curves. For a green, object, reduce magenta and for a blue object, work on yellow.

When converting to CMYK mode, Photoshop will always ask if you’d like to merge (or flatten) all the layers together. I suggest you do unless you have a very good reason not to (like if you want to create a shadow that will be printed using only black ink…see below). Otherwise, if you don’t flatten the image (merge all layers) before converting to CMYK mode, the blending of the layers will change and the quality of the image might suffer. Also, many blending modes (multiple, hardlight, etc.) might cause the image to use so much ink that the image might be troublesome on a printing press.

When using Curves, you can hold Shift and Command (Ctrl in Windows) while you click on your image to add a point to each of the C, M, Y and K curves representing t hat area of the image.

It is common to reproduce shadows using only black ink. It is usually thought that it is not possible to specify a black-only shadow while working in RGB mode, but it *is* possible. Select the area you would like to have printed only with black ink, then create a Channel Mixer Adjustment layer (From the Layer menu) and turn on the Monochrome checkbox. Now, if you convert the image to CMYK mode and don’t flatten it in the process, then that area will be reproduced using only black ink.

It’ very common that blue skies will seem to turn dark purple after converting to CMYK mode. To fix that problem, select the sky (using Select>Color Range perhaps) and then reduce the amount of Magenta in that area using Curves. This will produce a more cyan-ish blue sky and will be more like most of the skies you see in magazines.

If you are used to doing color correction by the numbers in CMYK mode (where you use neutral shades of gray), then the Color palette can be useful for calculating how much cyan ink is needed to produce a neutral gray. Just choose Grayscale Ramp from the side menu of the palette and then click and drag across the gradient to see the CMY mix needed to create any shade of gray.

If some of the tips this week seemed a bit more advanced than you’d like, don’t fret. With nearly 5,000 of you tip-hungry Photoshoppers on my list, I’m trying to offer something for all user levels. In the weeks ahead, I’ll be sure to include an equal dose of basic, step-by-step tips, along with some of the more complex ones. If you’d like to know how to color correct your images, then be sure to check out my book, or my national seminar tour at www.digitalmastery.com. Talk to you next week.

-Ben Willmore
Founder, Digital Mastery