Using the Calculations command

The Calculations command lets you blend two individual channels from one or more source images. You can then apply the results to a new image or to a new channel or selection in the active image. You cannot apply the Calculations command to composite channels.

To use the Calculations command:

1. Open the source image or images.

Note: If you are using more than one source image, the images must have the same pixel dimensions.

2. Choose Image > Calculations.
3. Select Preview to preview the results in the image window.
4. Choose the first source image, layer, and channel. To use all the layers in the source image, choose Merged for Layer.
5. Select Invert to use the negative of the channel contents in the calculation. For Channel, choose Gray to get the same effect as would be obtained by converting the image to a grayscale image.
6. Choose the second source image, layer, and channel, specifying further options as described in step 5.
7. For Blending, choose a blending mode.

For information on the Add and Subtract modes, see About the Add and Subtract blending modes. For information on other blending modes, see Selecting a blending mode.

8. Enter an opacity to specify the effect's strength.
9. Select Mask if you want to apply the blending through a mask. Then choose the image and layer containing the mask. For Channel, you can choose any color or alpha channel to use as the mask. You can also use a mask based on the active selection or the boundaries of the chosen layer (Transparency). Select Invert to reverse the masked and unmasked areas of the channel.
10. For Result, specify whether to place the blending results in a new document, or in a new channel or selection in the active image.