How To Use Cmyk Image With Calculation Command

By Author: Trisha White
Total Articles: 7
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Photoshop's Calculations command hasn't been a real attention-getter. However, it still holds interesting possibilities for enhancing images both technically and creatively. On the more technical side, there are many different image problems related to correction for print. One that isn't commonly addressed is color depth. At some point, you may receive an image that has good color but still appears a little flat and lacks depth or richness.

Images without depth can be enhanced by adding more detail to the Black channel. One way to enhance an image such as this is to create a new Black channel that contains more detail and contrast. You can do this easily by using the Calculations command to blend the existing Black channel with one of the other color channels that has more detail in it, thus creating a new channel with the desired attributes. This command helps in creatively enhancing your images.

How it works

The Calculations command works by manipulating pixel values with blending modes, just like the blending modes in the Layers palette. Each pixel in an image channel can have a brightness ...
... value from 0 to 255. By adjusting these values, a new and improved channel can be created. Here the main focus is on CMYK.

Analyzing the image

Open a CMYK image you want to work on and then click on the Channels palette. It's quite apparent how low contrast the Black channel is. By looking at the other channels, we determined that the Cyan channel would be the best choice to combine with our Black channel. It has more detail as well as similar tonality to the Black channel. We could copy the channels into different layers and combine them with the blending modes, but we'll make this combination far more easily with the Calculations command. Boost an image's detail by combining it with the Cyan channel.

Now that you know a little about how Calculations works and which channels you want to work with, choose Image > Calculations. Select the Preview check box so you can see the results of your combinations in the image window. Then, at the bottom of the dialog box, select New Channel from the Result pop-up menu to specify that you want the resulting blend to be placed in a new channel in the active image. Now, choose the Source 1 image and channel from the respective pop-up menus. You can choose from any open image (of the same size) and any layer or channel within that image. In this case, select the Cyan channel.

Creative calculations

The Calculations command isn't just for correction purposes. You can also use it to make creative image combinations. Since you can take channels from two different images, you can composite photographs into something more graphical.

Combination stree

To begin, open two images that are of the same size, resolution, and color mode. Both images must be open for the Calculations command to access them. Whichever of the two images is selected appears as both the Source 1 and Source 2 image. Choose the second image from the Source 2 pop-up menu. From each Channel menu, select a different color channel. You'll have to experiment until you get a combination that looks promising. If you want to work with a grayscale version of one of the images, you can do so by selecting the Gray option from the Channel pop-up menu. You can also work with either the positive or negative of the channel image. By selecting the Invert check box, you'll switch to the negative version of the channel.

Masking techniques

Once you've selected your channels, experiment with the Blending and Opacity settings until you get an interesting effect. To refine the effect even more, you can also apply the blending modes through a mask. To do so, select the Mask check box. This extends the dialog box and lets you choose the image and layer containing the mask. From the Channel pop-up menu, you can choose any of the color or Alpha channels in an image to use as the mask. You can also use a mask based on the active selection or the boundaries of the chosen layer. As with the other channels, you can also invert the mask.

Once you've created a good effect, make sure your Result setting is set to New Channel and then click OK. Repeat this process two more times until you have three different-looking channels.

Assembling a new image

Now that you have three channels to work with, open a new CMYK document of the same size and resolution. Next, copy and paste the Alpha channels into the color channels of your choice. You'll get different color effects depending on what channels you choose to paste into. You can of course do this same effect with four channels, but the colors tend to become somewhat neutralized.

Customizing channels

You can see that the Calculations command is both a creative device and a color correction tool. By mixing and masking your channels you can come up with an almost infinite variety of effects.

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