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Step 1. Open the files for the left and right images of the stereo pair and ensure that they are correctly oriented, with the axis of rotation (8-10°, unless vertical exaggeration is desired) aligned vertically. The process is easier if the images are of the same pixel dimensions, and it is usually helpful to give the files names that indicate which image is left and which right (in this example they are called Xleft.tif and Xright.tif)
Step 2. Taking one image first, in this case Xleft.tif, the image for the left eye (acquired at + 4° relative to horizontal), from the Image menu, select Mode > RGB Color.
Step 3. From the Image menu, select Adjust > Levels (or Adjustments > Levels in Photoshop 7)
Step 4a. In the Levels window, from the Channel pop-up menu, select Green.
Step 4b. Set the Output Levels to 0 and 0. The image should now appear purple.
Step 4c.Stay in the Levels window, and from the Channel menu select Blue.
Step 4d. Set the Output Levels to 0 and 0. The image should now appear red.
Step 4e. Stay in the Levels window, and from the Channel menu select Red. If the Red channel's histogram is truncated or skewed, adjust the sliders accordingly to improve image contrast and brightness (this step is optional, but can significantly improve the quality of the final stereo image)
Step 4f. Click OK to close the Levels window.
Step 5. Make the right image of the stereo pair (Xright.tif in this example) the active window (acquired at + 4° relative to horizontal), from the Image menu, select Mode > RGB Color.
Step 6. From the Image menu, select Adjust > Levels (or Adjustments > Levels in Photoshop 7). Repeat steps 4a-b for the Red and Blue channels. The image should now appear Green. Repeat step 4e for the Green channel (optional).
Step 7. From the Layer menu, select Duplicate Layer. In the Duplicate Layer window, in the Destination, Document pop-up menu, select the file containing the left image (in this case Xleft.tif) and click OK.
Step 8. Make the left image the active window (in this case Xleft.tif). It will now have two levels (shown in the Layers palette) the uppermost of which will be the right image that you just duplicated in step 7.
Step 9. In the Layers palette, from the Layers pop-up menu select Screen.
Step 10. If necessary, adjust the position of the uppermost layer to maximise the alignment of the two images. The anaglyph stereo pair is now complete and should look three-dimensional when viewed using red-green viewers. The image should be saved in the format best suited to the purpose of the image. To avoid loss of information through image compression and preserve the layers, which will allow for future adjustments to be made, save as a Photoshop format file. If the image is being prepared for publication, a file format that does not involve loss of information during compression is best, probably TIFF or EPS (not JPEG). For use on the www or in a Powerpoint presentation, adjust the pixel dimensions of the image downwards to a size that is suitable (i.e. no more than 1024 x 768 for Powerpoint), and if no further editing will be required, save as a JPEG file, with appropriate compression.