SCANNING

STEREO PAIRS

Unless you do your photography with a digital camera, a scanner is your basic tool for getting your images in digital form - an essential prelude to using any sort of stereo editing software. Your needs with respect to a scanner will depend on whether you are working from prints or directly from film.

Scanning Prints

If your are working with conventional cameras (35mm or APS) using a twin-camera rig or a slide-bar, you can get your pictures processed at any local processor (one-hour or over-night) and you will get prints returned with your color negatives. If your local processor can print Realist-format negatives, you will also be working with prints.

Any standard flat-bed scanner will handle your print-scanning chores. These days, perfectly acceptable scanners can be purchased for well-under $100. You should scan at 300 dpi resolution with 24-bit color. I scan color prints in color, even if I will eventually be using them for grayscale Holmes stereoviews. Converting color images to gray-scale usually produces images of slightly higher quality then doing the scan in the gray-scale mode.

Since control of image size and registration is always an issue when working with stereo pairs, it is important to try to position each print the same way when scanning. I always orient each print so the upper and side edges are restrained by the top and side-edge of the scanner bed:

If you orient your prints precisely the same way for each scan, the registration of the image pair will be limited by how precisely each print was registered in the film processor/printer, not by position variations caused by your scanning.

Film Scanning

Being able to scan film directly, without making a print, is a boon to the Realist or European-format photographer who doesn't have access to a processor that can make the prints. Any one-hour lab can process the film and return it, uncut, without making prints. I have found the processing cost to run between $2.50 and $3.00 for a 24-exposure roll of color negative/print film.

Film scanners are a bit specialized for the average photographer, but prices have come down considerably. There are two distinctly different approaches to implementing a film scanner. The most readily available are models of conventional flat-bed scanners that incorporate film/slide scanning capability. There are three primary issues with these units:

• Scanning Resolution. These hybrid scanners are typically rated at around 1200 dpi in terms of scanning resolution, compared to 2400 to 3600 dpi for dedicated film scanners.

• Scanning Speed. Hybrid scanners are very slow when operating in the film-scanning mode. It can take several minutes to even do a preview scan and the actual full-scan can take much longer. You may not notice the time factor when working with a single image, but you can spend the an evening just doing the scans for a single roll of film! In contrast, dedicated film scanners can do a preview in 5-10 seconds and execute the detailed scan in under a minute!

• Film Handling. Film handling tends to be somewhat crude in the case of hybrid units. Dedicated units tend to have more sophisticated film holders and may automate or semi-automate many aspects of film handling.

You can do good or, at least, reasonable work with a hybrid scanner but it will be work and you will have to learn to make the most of your hardware and software. In contrast, dedicated film scanners produce sharper scans in a very short time with much less effort on your part. Despite this, dedicated units also have three drawbacks:

• Unit Cost. I have seen some models priced around $130, but the ones that earn really solid reviews tend to be in the $300-$1000+ range.

• Availability. These are specialized items that you won't find in most computer retail outlets, let alone discount stores. Generally you will have to order one or shop via the Internet. Fortunately the internet lets you browse reviews on the models you identify and the businesses selling them. The reviews often include detailed scanned images as well as lots of information, good and bad, on using each unit. As in most other tings, read as many reviews as possible as small numbers can be misleading.

• Learning Curve. Really learning to get the most out of a film scanner takes much more time than simply scanning a print. The result is a more extended learning curve, but typically superior results once mastered.

The Olympus LS-10 scanner, for example, has a street price of about $320. Canon has recently introduced their D660U flatbed scanner with a built-in film scanner. This unit, which has a street price under $200, does a superb job scanning prints in the normal flatbed mode but will also scan film (black and white negative, color negatives, or color positives) at 1200 dpi. While this does not equal the resolution of dedicated film scanners (3600 dpi and up), it is more than adequate for our use. The scanner uses a USB interface, so you must have Windows 98 or better as your operating system. Print scanning is very fast, as opposed to film scanning, which is quite slow. However, for price and versatility, it is hard to beat the features offered by this scanner! Given the nature of the marketplace, I would expect to see even more capable units come along, with a general trend toward falling prices.

As an example of the comparative resolution of flatbed and dedicated film scanners, here is a single Realist-format frame, scanned at 1200 dpi buts displayed at much lower resolution to fit this page:

While using the Canon flatbed scanner at 1200 dpi is definitely better than not using my Realist-format cameras, it does not deliver the full quality that these cameras can produce.

This set of images graphically contrasts results obtained with a Canon D660U flatbed scanner and a film adapter (1200 dpi on the right) with a Konica/Minolta Dimage Scan Dual IV dedicated film scanner (3200 dpi on the left). The images represent a small subset of the primary image, shown above, and the contrast is striking. While there is no loss in the 1200 dpi sample at this size, the effective resolution of the 3200 dpi image is reduced by about 50% as displayed! The resolution limiting factor at 3200 dpi is actually the grain of the film and the image pairs are stunning at full-resolution.

Of course there is always a price to be paid for increased quality. It this case it is storage of the archived image files. A base JPS stereo pair in the Realist-format will require 10-15 megabytes for storage - three times that required for images at the lower resolution. Fortunately, inexpensive archival storage is available in the form of CD-ROM disks, each one of which can archive approximately two 36-exposure rolls of stereo pairs.

Scanning Slides

Most film scanners are also set-up to scan slides. The standard holders accommodate 2x2 slides, but most can be adapter (one way or the other) to scan Realist-format slides:

This is a scan (much-reduced resolution to speed the on-line display) of a Kodachrome stereo pair from a 1968 trip through the redwood forests of northern California. If you want to see the image in stereo (640 x 600 resolution), just click on the image. The original photos were taken with a TDC Colorist stereo camera and photography was very demanding given the narrow exposure range of the Kodachrome and the huge brightness range between the deep forest and clearings such as this one by the roadside.

Image Size

Whatever the film format, it is critical that the two stereo pairs have the same dimensions. If they differ slightly, the Depthcharge Developer Studio software has a cropping utility that will "trim" the larger image to the same size as the smaller member of the pair, but it is always easier if they pair is sized properly to begin with. One of the nice things about digital cameras is that the images are always precisely the same size! In the case of scanned images, you set the size for each image by how you scan it.

The software for many scanners (including the Canon D660U) lets you precisely define the size of the actual scanning window after you have done a preview scan. For example, when scanning Realist-format negatives, I set the window or scanned area to 1100 by 1100 pixels. In most cases the images will end up precisely this size and, if they are off slightly, Depthcharge Developer can crop them to match. Once I have defined the size of the scanning window, I then zoom in as far as possible on the preview image and move the window to the same position relative to the exposed border of the image on the film. The more precisely you do this step, the better the registration of the final image pair. Some scanner software only lets you click and drag the edges of the window when previewing prior to the final scan. In such a situation, you should overscan slightly and then use a mask to crop the image to the final size, as shown below.

Using a Mask

The use of a mask to format your final image can perform two useful functions:

• Precise control of the image size where the scanning software will not let you set the final size with precision

and

• The ability to change the format or aspect ration of each element of the image pair

Regardless of why you use a mask, the technique is the same:

1. Create a new (blank) image that is precisely the size and/or aspect ratio that you want
2. Paste the original image onto the new one
3. Re-position the pasted image, if required
4. Save the new image as one member of your stereo pair
5. Repeat the process with the second element of the stereo pair

The original images for this stereo pair were 640 x 480 pixels - an aspect ratio very close to that of a standard print that you would get when shooting with a slide bar or twin-camera rig. This is fine for Internet viewing, but if I want to use the set to make a Holmes stereoview, the images should be essentially square.

Since I want to lose as little coverage as possible from the original picture, I created a NEW image with my graphics software that is 480 pixels square. I can then paste the original image into the new one and save the result:

The resulting image has precisely the size I want and I have also been able to precisely crop to achieve a perfectly square image which I can then use to create a Holmes stereoview. Masking is a very useful technique that cans solve image size and format problems with a high degree of precision.

Image File Formats

Probably the most common image format is JPEG, and it is attractive because the image files cam be quite small. However, it is image compression that is used to achieve the small file size and that can cause image degradation if you are manipulating and re-saving the image. JPEG can save you significant storage capacity without degrading images if you elect to save them at the minimal compression/highest quality setting your software provides.

Ralph E. Taggart (Gyrobee@aol.com)