Boston Grotto Photo Gallery

Technical Details about the photos

Techniques of Cave Photography

A variety of sources are available describing cave photography techniques and equipment. Later versions of this page will describe these in more detail and provide links.

Scanning and Image Preparation

Image enhancement was performed using Adobe Photoshop V3.0.

For most of the photos, the following steps are performed:

1. The scanner software, operating as a Photoshop plug-in, is used to scan a "preview" of the slide at screen resolution, and then a portion of the slide is cropped, focussed, and rescanned as a preview. The contrast and color correction curves supplied by the scanner software are not used in this step. The scanning resolution and image size settings for the final scan are chosen based on the intended use of the photo in this Gallery. Simple illustrations are scanned to small sizes (4" across), generally informative photos are scanned to medium sizes (6"-8") and large sizes are used for particularly dramatic shots suitable for use as screen backgrounds (10" or more). The output resolution of the scan is set to 75 dpi, corresponding closely to the resolution of most monitors, or 150 dpi for the better shots. Even though the final result will always be converted to 75 dpi, it often helps to have more pixels initially to avoid losing detail during the editing process. This step takes about 5 minutes per photo.
2. The scanner performs the scan according to the setup from step 1. This step takes about a minute per photo.
3. Most photos have excessive contrast and are too dark to use directly, so the "Levels" feature in Photoshop is used to adjust the contrast and brightness. Often, with cave slides, it's necessary to independently adjust the contrast for different areas of the photo. For example, in a photo with bright highlights and also interesting details in the dark portions, any adjustment to brighten up the dark areas would wash out the highlights, so Photoshop's selection tools: wand, lasso, etc., are used to select different portions of the photo and apply independent adjustments. Sometimes a detail as small as a person's face is selected and brightened for maximum effect.
4. The contrast and brightness adjustment usually alters the color balance of the photo, usually toward excessive green. This is corrected by using the color balance feature of Photoshop.
5. Even when the photo is scanned at high resolution, some of the sharpness of the original photo is lost. The "Unsharp Mask" feature of Photoshop is used to sharpen the edges and boundaries of the scanned image. This brings back some of the resolution lost in the scanning process and often has the interesting effect of "livening up" the image. Modern display devices (monitors, dot matrix and laserprinters) do not yet approach the resolution of a photographic print or projected slide, but quite acceptable results can be achieved in practice, especially with the very wide dynamic range of CRTs.
6. If necessary, scratches, dust specks and other slight imperfections of the slide or negative itself are removed using various selection and masking features of Photoshop.
7. On some of the shots, the original photograph contained an imperfection such as lens flare, under or over exposure, or focus problems. These imperfections can be remedied, to a degree, using Photoshop's extensive image manipulation capabilities. We endeavor to present the scene as the photographer intended it to be viewed when making the original exposure. On rare occasions, we use Photoshop's "Cloning" tool to erase an undesired object accidentally left in the scene, such as a piece of caving equipment or a person's head. These 5 steps require at least 5-15 minutes per photo, depending on how much correction is needed, but it's possible to get carried away and spend an hour or more!
8. The processed photo is named and saved in its original resolution and Photoshop format for archival use, and backed up on tape. A typical photo uses 2 MB to 5 MB of disk space, though some are much bigger where the Photoshop work results in multiple layers.
9. The processed photo is converted to JPEG form and downsampled to 75 dpi, and a small "thumbnail" GIF version is also produced at 75 dpi and about 1" across to use as inline images on the web pages.
10. The JPEG and GIF versions are uploaded to the Web server. Usually, many photos are uploaded at one time, the time depends on the network load and the size of the photos. Several hundred K bytes can be uploaded in 10-15 minutes using a 28.8 modem.
11. The images are viewed on a variety of monitors to see if the brightness, contrast, and color balance look OK. The process is repeated until acceptable results are obtained.
12. Pointers to the completed photos are inserted on these pages.

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