getting started with photoshop - Channels & its features (4)

Using the Apply Image command

The Apply Image command lets you blend one image's layer and channel (the source) with a layer and channel of the active image (the destination).

To use the Apply Image command:

1. Open the source and destination images, and select the desired layer and channel in the destination image. The pixel dimensions of the images must match for image names to appear in the Apply Image dialog box.

Note: If the color modes of the two images differ (for example, one image is RGB and the other is CMYK), you can copy a single channel to another channel between images, but you cannot copy a composite channel to a composite channel in another image.

2. Choose Image > Apply Image.

3. Choose the source image, layer, and channel you want to combine with the destination. To use all layers in the source image, select Merged for Layer.

4. Select Preview to preview the results in the image window.

5. Select Invert to use the negative of the channel contents in the calculation.

For Blending, choose a blending option.

7. Enter an opacity to specify the effect's strength.

8. Select Preserve Transparency to apply the results only to opaque areas in the result layer.

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.

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.

For Blending, choose 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.

About the Add and Subtract blending modes

The Add and Subtract blending modes are available only for the Apply Image and Calculations commands.

Add

Adds the pixel values in two channels. This is a good way to combine nonoverlapping images in two channels.

Because higher pixel values represent lighter colors, adding channels with overlapping pixels lightens the image. Black areas in both channels remain black (0 + 0 = 0). White in either channel results in white (255 + any value = 255 or greater).

Add mode divides the sum of the pixel values by the Scale amount and then adds the Offset value to the sum. For example, if you wanted to find the average of the pixels in two channels, you would add them, divide by 2, and enter no Offset value.

The Scale factor may be any number between 1.000 and 2.000. Entering a higher Scale value darkens the image.

The Offset value lets you lighten or darken the pixels in the destination channel by any brightness value between +255 and -255. Negative values darken the image; positive values lighten the image.

Subtract

Subtracts the pixel values in the source channel from the corresponding pixels in the target channel. As with Add mode, the result is then divided by the Scale factor and added to the Offset value.

The Scale factor may be any number between 1.000 and 2.000. The Offset value lets you lighten or darken the pixels in the destination channel by any brightness value between +255 and -255.