MHS Resources: Making Anaglyphs from Stereoviews
by Gordon Goldsborough
The process of making red-blue anaglyphs from historical stereoviews is not hard, so long as you have the right software and remember a few things. I use Adobe Photoshop CS2 (at writing, the latest version) but the same things can be done with most image processing software.
There are several web sites that describe the process, and I have boiled it down to the following four steps.
Scan in color at a resolution of at least 300 dpi. (I prefer 600 dpi or higher so I have lots of pixels to play with.) You may wonder why one should scan a black-and-white photograph in color? Two reasons: 1) you preserve the original color of the mount, which may be interesting in itself, and 2) you will not have to convert the scanned image into color during later steps. You do not need a fancy scanner for this; I use a model that I bought for slightly over $100 at a local consumer electronics store.
Press them flat: Many early 20th-century stereoviews are curved, apparently on the thinking that this promotes the 3D effect when they are viewed in a stereoscope. Of course, this makes them harder to scan them on a flatbed scanner. I have found no recourse to pushing down on the scanner lid so it presses the stereoview flat. Otherwise, the center of the scanned image will be out-of-focus. You sometimes must press hard for thicker cards. Fortunately, the cards are quite resilient; I have damaged no cards during scanning - they always spring back into shape when the lid is opened.
Scan them straight: When placing the stereoview on the scanner platen, try to do it as perpendicular to the scanning direction as possible so the scanned image will be straight. Slight variation is not a big problem, and most software can straighten images that are not straight but I find that it is always better to start with as good a scan as possible, and rely as little as possible on software to fix problems.
Save the file as an RGB (red-green-blue) image in TIFF format. Do not use JPEG format at this stage, as it discards important data in the image and eventually causes it to degrade visibly.
Select the image: Assuming the scanned image is straight, select a rectangular portion to use as the basis for your anaglyph. I am planning to create an anaglyph that is square whereas most stereoview images are taller than wide so I necessarily have to discard some part of it. In this example, I will crop the uppermost part of the image. It has no interesting detail anyway and, that way, we avoid the rounded top of the image.
Go back to the original stereoview scan. Move the selection marquee from the right image to the left one, being as careful as possible to cover the same part of the image. (In other words, if you did not select the entire right image, then you should make sure to select about the same proportion of the left image.) When you have made a selection of the left image, select its red channel in the Channel window.
This is the most important step, so be sure not to skip it!
You may be inclined to stop at this point. You can look at this image with 3D glasses and it should look somewhat three-dimensional, but we can do better. This raw anaglyph probably has lots of blurriness, with “ghosts” around many of the objects in it. We must align the layers to maximize the three dimensionality.
Select the foreground. Pick an object in the anaglyph that you want to occupy the foreground of the three-dimensional image. In the above example, I chose the lead dog in the pack. All other dogs, as well as the people and the building should appear behind the lead dog.
Zoom in on this foregound object. To fine-tune the positioning, I zoom in on the lead dog, then make sure that I am viewing all color channels but the red channel is the active one. (The red channel is highlighted in the Channels window.)
After a bit of tidying up, cropping the image, resizing it to the desired final dimensions (in my case, 800 pixels by 800 pixels, at a resolution of 72 dpi) and adjustment of levels to improve contrast, we are done. Here is my version of the anaglyph:
Page revised: 10 September 2013