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1.2 and an Offset of 60. Note that Add automatically respects the transparency mask of the face layer, regardless of whether or not you select the Preserve Transparency check box.Applying the Subtract command
To create the first example in Figure 13-49, I selected the Subtract option from the Blending pop-up menu, once again accepting the default Scale and Offset values of 1 and 0, respectively. This time, the face turned pitch black because I subtracted the light values of the face from the light values in the background image, leaving no brightness value at all. Meanwhile, shadow details such as the eyes and lips had little effect on the background because shadows range from very dark to black. Subtracting black from a color is like subtracting 0 from a number it leaves the value unchanged.
The result struck me as too dark, so I lightened it by raising the Scale and Offset values. To create the second image in Figure 13-49, I upped the Scale value to 1.2, just as in the second Add example, which actually darkened the image slightly. Then I raised the Offset value to 180, thus adding 180 points of brightness value to each pixel. This second image is more likely to survive reproduction with all detail intact.
Subtracting the other direction that is, applying the Subtract mode inside the Michelangelo Face image
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Part IV: Layers, Objects, and Text
produces a radically different effect, as verified by the final example of Figure 13-49. The mountains are generally quite dark, so they have little effect when subtracted from the face. In fact, by Subtract standards, this is a remarkably successful blend. The Calculations command The Calculations command performs a different function than Apply Image, although its options are nearly identical. Rather than compositing a source image on top of the current target image, Image ® Calculations combines two source channels and puts the result in a target channel. You can use a single image for both sources, a source and the target, or all three (both sources and the target). Although Photoshop previews the effect in the foreground image window, the target doesn't have to be the foreground image. The target can even be a new image. But the biggest difference is that instead of affecting an entire full-color image, as is the case with Apply Image, the Calculations command affects individual color channels. Only one channel changes as a result of this command.
Choosing Image ® Calculations displays the dialog box shown in Figure 13-50. Rather than explaining this dialog box option by option I'd just end up wasting 35 pages and repeating myself every other sentence I'll attack the topic in a less structured but more expedient
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Figure 13-50: Use the Calculations command to mix two source channels and place them in a new or an existing target channel.
When you arrive at the dialog box, you select your source images from the Source 1 and Source 2 pop-up menus. As with Apply Image, the images have to be exactly the same size. You can composite individual layers using the Layer menus. Select the channels you want to mix together from the Channel options. In place of the full-color options RGB, Lab, CMYK each Channel menu offers a Gray option, which represents the grayscale composite of all channels in an image.
The Blending pop-up menu offers the same 20 blend modes including Add and Subtract found in the Apply Image dialog box. However, it's important to keep in mind how the Calculations dialog box organizes the source images when working with blend modes. The Source 1 image is equivalent to the source when using the Apply Image command (or the floating selection when compositing conventionally). The Source 2 image is equivalent to the target (or the underlying original). Therefore, choosing the Normal blend mode displays the Source 1 image. The Subtract command subtracts the Source 1 image from the Source 2 image.
Half of the blend modes perform identically regardless of which of the two images is Source 1 and which is Source 2. The other half including Normal, Overlay, Soft Light, and Hard Light produce different results based on the image you assign to each spot. But as long as you keep in mind that
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493 Photoshop CS Bible @Team LiB
Source 1 is the floater hey, it's at the top of the dialog box, right? you should be okay.Tip The only mode that throws me off is Subtract, because I see Source 1 at the top of the dialog box and naturally assume that Photoshop subtracts Source 2, which is underneath it. But wouldn't you know, this is exactly opposite to the way it really works. If you find yourself similarly confused and set up the equation backwards, you can reverse it by selecting both Invert options. Source 2 minus Source 1 results in the same effect as an inverted Source 1 minus an inverted Source 2. After all, the equation (255 Source 1) (255 Source 2), which represents an inverted Source 1 minus an inverted Source 2, simplifies down to Source 2 Source 1. Then again, if math isn't your strong suit, don't worry. I was just showing my work.