Quicklinks to all course lessons: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Lesson 10 Sections: 10-1 10-2 10-3 10-4 10-JFF 10-IDEA
Lesson 10 Sections: 10-1 10-2 10-3 10-4 10-JFF 10-IDEA
(10-3) Using the Calculations dialog
You've learned about the Apply Image command, which allows you to apply one image or layer to another using the blending modes. Located right next door to it in the image menu, the calculations command is similar except it gives you even more options than the apply image command. The calculations command is most often used to help you quickly define masks or alpha channels in order to make a selection quickly. Please watch the videos on this page to get a feeling for how the calculations command works. After you've finished this section, you should understand and feel comfortable using the calculations dialog.
Every color image is made up of greyscale channels that indicate the levels of a color in an image. In the image above, which is an RGB (red, green, blue) image, you can see each of the channels. The lighter the value in any channel, the more of that color in the image. For example, you'll notice that the red channel has the lightest face, because there is more red in the face than there is in the green and blue channels. You'll notice her eyes, which are greenish blue, are darker in the red channel, because there is very little red in her eyes. The lighter the value showing in a color channel, the more of that color there is in the image. White in an image would be 100% in all the channels. Black would be 0% of that color in all of the channels. Here's a link to the image.
So, I'm going to focus on her freckles - they show up best in the blue channel. I duplicated the blue channel as an alpha channel - blue copy. With that selected, I go into the image menu and choose calculations. In the illustration below, I am going to merge the green channel (source 1) with the blue copy channel (source 2). I can then choose the blending mode I wish to use to merge those two together, as well as the opacity (or amount of the effect). This gives me very pronounced freckles, and awesome eyes.
So, I'm going to focus on her freckles - they show up best in the blue channel. I duplicated the blue channel as an alpha channel - blue copy. With that selected, I go into the image menu and choose calculations. In the illustration below, I am going to merge the green channel (source 1) with the blue copy channel (source 2). I can then choose the blending mode I wish to use to merge those two together, as well as the opacity (or amount of the effect). This gives me very pronounced freckles, and awesome eyes.
So, let's see what happens if I use channels and the calculations command to lessen her freckles. The red channel is best for that, so I'll duplicate it into a channel I've named Alpha 1. Bringing up the calculations dialog, I choose to merge this red alpha 1 channel with itself (so it's both source 1 and source 2). I choose to use the overlay blending mode with an opacity of 40%. I also choose to mask out the blue channel (and I've inverted the mask). You can see the result below.
Now watch the three videos below. These will help you understand how to select hair more accurately by using the calculations dialog. It will take you about 45 minutes, but you'll learn a lot about using these powerful tools to do some pretty tough selections.
Video: Advanced Tutorial: How to Select Difficult Hair in Photoshop CC (34:39)
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Video: Photoshop tutorial: Calculating with the Add mode | lynda.com (6:07)
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Video: How to mask blonde hair in Photoshop | lynda.com tutorial (4:58)
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