Create stunning effects with colour channels

1. Open your images
Choose three frames from a sequence taken with a tripod and the same camera settings - such as those on your Video Disc. Open them in Photoshop.

2. Merge three into one
Click the Background layer icon on one shot, hold Shift and drag it into the main window of one of the other shots. Add the third image in the same way.

3. Spot the difference
Check that the stationary elements are in perfect alignment in your combined image by changing the Blending Mode for Layers 1 and 2 to Difference.

4. Nudge into position
Turn off Layer 2 and click on Layer 1. Use the Move tool to nudge Layer 1, maximising the amount of black and minimising halos in the shot.

5. Nudge again
Click on the eye symbol next to Layer 1 to turn it off and Layer 2 to turn it on. Click on the icon for Layer 2 and select the Move tool. Use the arrow keys to nudge this into perfect alignment with the Background. Set the Blending Modes of Layers 1 and 2 back to Normal (from Difference), then make Layer 1 visible.

6. Unlock the base layer
You can now combine the three layers so that each represents just one of the three primary colours. First, you'll need to unlock the Background layer. To do this, double-click on its icon in the Layers palette. A window will appear, giving you the option to rename the layer, but you can leave this as the default 'Layer'. Click OK to confirm the settings.

7. Advanced blending
Double-click on the icon for Layer 0. This time, a Layer Style option box will appear. This provides advanced settings for blending different layers. You'll see that in the Channels options, R, G and B are all checked. Uncheck the Green and Blue buttons so that the bottom layer shows just the Red channel.

10. Switch back to RGB
We want the new top layer (Layer 2 Copy) to appear in full colour (not just in green), so double-click on the Layer icon and ensure that the R, G and B channel options are checked. However, we only want this full-colour version to appear selectively, otherwise we lose the Harris Shutter tricolour effect.

11. Put on a mask
The next step is to create a mask for the top layer. You can do this by clicking on the Add Layer Mask icon at the bottom of the Layers palette. This will appear as a white square next to the active layer. The mask is initially completely transparent and has no effect on the layer. In order to start painting on the Layer Mask, you'll need to make it opaque.

12. Start painting
Make the Layer Mask opaque by clicking on the Mask icon and pressing Alt+Delete. The Mask icon in the Layers palette will turn black. You can now use a Paintbrush, set to white, to reveal areas of the combined image. This increases the detail in the raspberries and adds a white core to the sugar.

13. Save and flatten
Do your mask painting gradually, until you're happy with the result. If you make a mistake and overdo the effect, use the History palette to go back a few steps. Save the document in the Photoshop (PSD) file format so that you can re-edit the layers in the future. When you're done, merge all the layers together by going to Layer > FlattenImage.

14. Stamp and sharpen
You can now retouch the image by using the Clone Stamp tool to remove any specks of colour you feel are in the wrong place. The final step is to sharpen the combined image. Choose Unsharp Mask from the Filters menu and choose options that give enough detail without adding noise and artefacts.