Combining Image Channels
Combining Image Channels
The Calculate Image command lets you combine channels to create selection masks for effects like embossing text in an image. By adding, subtracting, and multiplying channels, you can also enhance shadows and highlights. The Calculate Image command combines corresponding pixels from two channels by the method you choose. You can place the result in a new or existing channel.
As shown in Examples of Calculate Blending Options, you can also copy an image and paste it into a new alpha channel of Source 1. Then use the Calculate Image command to combine Source 1 and the new alpha channel (Source 2).
To Combine Channels:
- With an image in Edit mode, choose Image | Calculate.
- Choose the first channel in the Source 1 menu. If you want to invert the channel, select Invert. For more information, see Inverting Colors in Images.
- In the Source 2 menu, choose the channel you want to combine with the Source 1 channel. If you want to invert the channel, select Invert.
- In the Blending area, choose an option in the Use menu. See Descriptions of Calculate Blending Options.
- Enter an opacity from 0 to 100 percent for Source 1. Other options are available for some Blending methods.
- If you want to mask Source 1, select Mask in the Blending area and choose a channel in the menu. To invert the mask, select Invert in the Blending area.
- Choose the name of a destination channel or choose New in the Result menu. If you select an existing channel, Canvas X Draw replaces the channel with the results of the Calculate Image operation.
- Click OK to calculate the channel using the current settings.
Descriptions of Calculate Blending Options
You can select various blending methods in the Calculate Image dialog box.
Places Source 1 over Source 2 at the specified opacity. 100 percent opacity replaces Source 2 with Source 1. | |
Multiply | Creates a darker channel than the source channels. Black areas in either source create black areas in the resulting channel. White areas do not affect the result. |
Screen | Creates a lighter channel than the source channels. White areas in either source create white areas in the resulting channel. Black areas do not affect the result. |
Overlay | Places Source 1 over Source 2 without destroying the shadows or highlights of Source 2. |
Soft Light | Lightens or darkens pixels in Source 2 depending on the brightness value of the corresponding pixels in Source 1. Pixels in Source 1 that are lighter than 50% black lighten Source 2. Pixels in Source 1 that are darker than 50% black darken Source 2. |
Hard Light | Lightens or darkens pixels in Source 2 depending on the brightness value of the corresponding pixels in Source 1. Hard Light works similarly to Soft Light. However, black in Source 1 produces black in the resulting channel and white produces white. |
Replaces pixels in Source 2 with the corresponding pixels in Source 1, if the pixels in Source 1 are darker. | |
Lighten | Replaces pixels in Source 2 with the corresponding pixels in Source 1, if the pixels in Source 1 are lighter. |
Add | Creates a lighter channel than the source channels. Add is similar to Screen but usually produces a higher-contrast image. If you select the Add option, you can enter a Scale value from 1 to 2 with a precision of three decimal places. To calculate the average brightness value of two channels, choose Add and enter a Scale of 2. You can brighten or darken the resulting channel by specifying an Offset value. To lighten the overall image, enter an offset from 1 to 255. To darken the image, enter an offset from -1 to -255. |
Subtract | Creates a darker channel than the source channels. Subtract is similar to Multiply. However, corresponding pixels of the same color produce black in the resulting channel. If you select the Subtract option, you can enter a Scale value from 1 to 2 with a precision of three decimal places. You can brighten or darken the resulting channel by specifying an Offset value. To lighten the overall image, enter an offset from 1 to 255. To darken the image, enter an offset from -1 to -255. |
Difference | Compares the color value of each pixel in Source 1 with the corresponding pixel in Source 2, subtracts the darker value from the lighter, and then uses this difference in the resulting channel. |
Examples of Calculate Blending Options
 Source 1 |  Source 2 |  Multiply |
 Screen |  Overlay |  Soft Light |
 Hard Light |  Darken |  Lighten |
 Add |  Subtract |  Difference |
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