Stereo Cards

How to Make Good Quality Stereocards from Digital Stereo Pairs

by John Ballou

In my last article in the Panoram, a method for aligning stereo pairs was presented, which was a guide to correcting any misalignment between the two images to form a stereo pair. After performing this task, it is easy to separate the two images and have them turned into 35mm slides, which can then be mounted for viewing through a hand viewer or projected on the silver screen. The current cost which I am paying to have stereo slides made is about $5.50, not including shipping. Is there a less expensive way to view your digital pairs?

Indeed, there is. By doing a few additional adjustments, Holmes format cards can be made by printing the stereo pair on a standard 5″ X 7″ print, and then using double-sided photo mounting tape to attach the print to an appropriately-sized card.

Let’s start with a short statement of facts about digital photo printing. First, the cost of buying and operating your own photoprinter is pretty high. While the advertised DPI (dots per inch) sounds great on these models, it’s not clear that the additional resolution results in sharper pictures. A lot depends on the quality of the image captured by your digital camera, and on whether the resolution of the image matches exactly the resolution of the printer. This is because when there is a mismatch, the printer (or the software in it) must do a conversion from the native resolution of the camera to the resolution of the printer. This gives you problems no matter which element (the camera or the printer) has the higher resolution. If the printer is higher resolution than the camera, noticeable pixellation (the appearance of individual dots) can occur. Conversely, if the camera is higher resolution than the printer, the conversion that the printer software does to the image can result in details in the image being lost.

To test this out, I used a high-resolution stereo pair that I took this summer, and had it printed on different digital printing systems. I also tried printing it at different resolutions. The results pretty much confirmed my hypotheses in the paragraph above. This led to the obvious question: What resolution is optimum for use with the ubiquitous photo printing machines that can be found at Target, Wal-Mart, and different drugstore chains?A little internet sleuthing turned up a number: Most printers in common usage for digital printing have a native resolution of 300 DPI. This doesn’t necessarily mean that the machines will clearly print an image at that resolution, but that is what it is designed to do.

Many prints were made by Target, Wal-Mart and others which seemed adequate, but one of the Golden Gate Stereoscopic Society members suggested going to Walgreen’s drugs and checking out the “Frontier” systems. This was an eye-opener. The prints from those machines were far and away sharper and clearer than the prints done on other machines. One big drawback:They don’t currently accept Thumbdrives – those small USB connected flash memory devices. I have to burn a CD to get my pictures into that machine. I have since found that Wolf Camera or RitzPix will accept uploads from the internet to their website, and produce your prints in one hour. Current cost for a 5″ X 7″ print is $0.99. They also offer the option of printing on matte finish paper, which I prefer because it eliminates reflections, which can be a problem in a hand viewer.

So, how do we go about placing our two chips on a 5″ X 7″ print so that they will be viewable using a Holmes viewer?

Well, since we have the resolution of the photo printing machine (300 DPI), we just do a little math, and we have a size of 1500 X 2100 Pixels. Given that, how wide should we make the images to fit properly? Well, most Holmes viewers allow for images to be further apart than standard interocular spacinc, let’s make our images 3″ wide. I have found that a gap between the images of 80 pixels (about .233″). That gives us images that are 3″ wide, or 900 pixels. This means that we must resize the stereo pair to be 1800 pixels wide. (2.5″ X 2 X 320 DPI)

What I usually do is to take my stereo pair (aligned using the method described before), and resize it to be 1800 pixels wide, retaining the aspect ratio in proportion to this. At this point, it is important to do any sharpening or other manipulation that is necessary to correct for the resolution change. I usually just sharpen a small amount, and do any brightness/contrast/color balance changes at this time. Then, I create a new picture sized 1500H X 2100W pixels. If your software uses inches, just divide 1500 and 2100 by the number of pixels per inch: 72DPI will yield 20.833 X 29.2. If you can, just set the DPI to 300, and then it’s 5 X 7.

Then, import your image pair into a new layer. Make sure that the image is centered in the frame, then select one half of the stereo pair, and move it 40 pixels away from the other image. Then, select the other half, and move it 40 pixels the other way. This should result in the placement in the diagram below:

After you’ve placed the images in the proper location, use the text editor to add a title to the bottom of your stereocard. You can place the text on one side as shown above, or put it on both sides to make a stereo title. If you do, make sure that the text has the same location in the vertical direction, and adjust the horizontal spacing of the text to place it at the stereo window. What I usually do with this is make the image small enough to free-view it with my eyes parallel, and move one text field right and left until it seems to be in the stereo window. You can also experiment with putting some fields of the text forward of or behind the stereo window to create emphasis or interest.

For backing, I go to a stationery store, and purchase 28″ X 22″ black card stock. Then, you can go to Kinkos’ and use their large roll cutter to cut it into four 6 15/16″ strips, then cut those strips into seven 4″ high cards for mounting. You can also make some 3.5″ high cards for landscape stereo pairs.
