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Three Ways to Isolate Color

(February 2009) posted on Fri Feb 20, 2009

Determining the best way to separate images in Photoshop can be a challenging decision. This month, Trimingham narrows the playing field with three useful approaches to color separation.


By Thomas Trimingham

click an image below to view slideshow

The simplest way to demonstrate this method of separation is to take the guitar image and then split it using the Image Mode. First the color settings need to be adjusted to custom CMYK and a setting of GCR using a maximum on the black (Figure 4). This step is essential for an image with a black background. Without it, the CMY channels will be polluted with the surrounding black and fundamentally less effective as source selections from which to pull colors. In this example, I converted a duplicate file of the guitar image to CMYK using Image Mode with the proper settings and then analyzed the CMY channels one at a time to see whether I could use the color information in different areas of the channels as elements in the final separation set.

The largest drawback to this method of separation is you may have to make extra selections to create the final separation set because you’re bound to find additional colors or polluted areas in the CMY channels. This is where some skills with the Magic Wand (as previously explained) and even the Color Range tool become essential to save serious time. The goal, as stated before, is to avoid the complex path approach at all costs because of the time it wastes. Experience will tell when the best method is to create an extra layer and squeeze out some items using the Magic Wand or when it’s better to just bite the bullet and create a path and be done with it.

The M and Y channels from the duplicate image were very useful in creating the base for the final yellow, orange, and red channels because the guitar image had a lot of reds and yellows. Ultra smooth gradients, like those in flames or airbrushed drawings, are ideal to isolate and separate by using Image Mode to create channels from which to pull colors. To create the red channel, I selected areas of the magenta channel, copied, and then pasted into the final separation set. A common way to do this is to create a new channel, paste in the information from the original separation of CMYK, and then use the Curves menu to curve out specific areas that will pollute other colors or need to be bumped up or down (Figure 5).

Every tool has its place

The final result of using these three methods in combination is the best quality set of separated colors in the least amount of time. The way that these tools are used varies and changes depending on the needs of the artwork, but each tool has a place in the total array of methods needed to achieve a great set of separated colors. Learning how the tools work together provides you with a unique combination of ways to isolate colors. And if they are also used in combination with layers and channels in alternating patterns, your ability to quickly handle very complex jobs can be dramatically increased.

If things don’t develop properly during the separation process, it’s because the colors can’t be isolated from other colors or the value ranges that are selected are ragged and don’t blend well. The trouble often starts at the beginning of the process and relates to decisions an artist makes about how to set up the separation set. The wrong choices made at the start of a separation set can cause an artist to choose and split out a color selection without digitally testing it. Some of this can be ego, or trying to rush the process, but no one wins when the odds are doubled that the final print will turn out poorly and the press will sit idle while the separation are redone.

Thomas Trimingham has worked in the screen-printing industry for more than 15 years as an artist, art director, industry consultant, and head of R&D for some of the nation’s largest screen printers. He is an award-winning illustrator, designer, and author of more than 45 articles on graphics for screen printing. Trimingham can be reached through his Website, www.art2screen.com.


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