Apply Image lets you composite images together on the same layer and use a number of expressions for advanced channel blending.
About Apply Image
Apply Image lets you blend a layer from a source image into a target image's layer. The images are composited into a single layer. Channel expressions and blend modes are available to composite the layers.
The source image can be scaled automatically to the target image horizontally, vertically or both, avoiding having to size the images equally first.
To blend two images:
Open your target image.
From the Layers panel, select the layer that you want to blend the source image with.
From the Filters menu, select Apply Image.
Click Load Image and navigate to, then select the source image to import. If the image is another layer within your document, you can also click-drag it onto the dialog box to use it.
(Optional) Check the Equations option in order to enable channel blending.
(Optional) Set the Opacity level to control how transparent the imported image appears.
Select a Blend Mode to alter how the source image's colours blends with the target image. Select from the pop-up menu.
(Optional) Uncheck Scale Horizontal To Fit to retain the imported images native width. When checked, the image is stretched/shrunk to the main image. Uncheck Scale Vertical To Fit to retain native height.
To use channel expressions:
With the Apply Image dialog open, either load an image or choose Use Current Layer As Source to blend the image with itself.
Check the Equations option in order to enable channel blending.
Choose a colour space to blend in with the Equation Colour Space dropdown.
Now use the available expressions to blend channel information. Some expressions include:
Use D+Channel to specify a destination image channel (the original layer). E.g., DB for Destination Blue channel.
Use S+Channel to specify a source image channel (the image you have loaded in). E.g., SR for Source Red channel.
Use +, -, *, / to add, subtract, multiply or divide respectively. E.g., SR/SG*SB to divide Source Red by Source Green and then multiply by Source Blue.