Today, more and more images are computer enhanced,
It is not uncommon for underwater photographers to discard as many as 90 per cent of their slides. Many of the throwaways are due to poor lighting or less than optimal composition. However, it is much more difficult deciding what to do with images that are in sharp focus and have interesting composition, but suffer from backscatter, unwanted objects in the frame or poor background colour.
The decision can be even more difficult to make if the dive trip was to an exotic, faraway place that you may never visit again. But rather than discarding those not-quite-perfect slides, there is an alternative: digital imaging. Generally, the phrase digital imaging means that a computer is used to alter/edit/enhance a photographic image. With digital imaging, the possibilities for photo manipulation go far beyond the few simple options, such as dodging, burning, or colour filtering, available at professional photo processing labs. For example, it can be used to eliminate backscatter, remove unwanted objects, such as a part of a diver or his equipment, or change colours.
There are three basic pieces of equipment used in digital imaging: an input device, a computer and an output device. For an input device, there are two main options: scanners and CD-Roms. If you already have a CD-Rom drive attached to your computer, you can have up to 100 of your images put on a single CD. A drawback is that after you edit the images, they cannot be stored back on the CD unless you have a relatively expensive device that writes on CDs. If you would like to do your own scanning, several companies, including Nikon, Polaroid, Kodak and others, market suitable scanners at moderate prices.
Another possibility is to have a professional company scan your images and put the resulting files on a portable hard disk. Storing digital images on floppy disks is not feasible because many diskettes could be required to hold a single, high-resolution file. Computers used for digital imaging have to be very fast, with huge amounts of memory. For example, for imaging to work effectively on a PC, the CPU (central processing unit) should be as near as you can get to the fastest currently available, such as the 200-megahertz Intel Pentium with 128 megabytes of random access memory (RAM). Less memory and slower computers can be used, but you will end up spending much time waiting as the computer shifts several renditions of your 32-megabyte files back and forth between memory and the hard disk.
In general, your time will be more efficiently utilised if your RAM is three to four times the size of the file being edited. Even with that much memory, your computer will need a large hard disk if you intend to store the edited files. You will be surprised to find how few 32-megabyte files, even when compressed, it takes to fill a 500-megabyte hard disk. Colour printers and film recorders are the most common output devices. The colour printer market has been exploding for the past few years and this explosion is expected to continue. However, only dye sublimation printers (the most expensive type of printer) produce photo-quality output.
It is also important to keep in mind that a large majority of people who want their slides digitally edited would like to have a new slide as the final product. Film recorders with their specialised cameras are used for this purpose, and several different resolutions are available. The terms 2K, 4K, 8K, etc, are used to specify resolution, with 4K meaning that there are a maximum of four kilobytes or 4,096 individual dots along the width of an individual frame. A 4K film recorder which outputs to 35mm film has a resolution of 4,096 x 2,731 or more than ten million dots that make up the image. Since one byte is required for each of the red, green and blue components of every dot, a total of 32 megabytes of information is required to fully define a 35mm image on a 4K film recorder.
For 35mm slides, a 4K resolution is usually sufficient,
unless you need accurate representation of very fine details. Keep in
mind that the critical feature of a film recorder is the 'spot size'
of each beam of light used to expose the film. If the spot size is large,
the 4,096 addressable lines in a 4K film recorder may be functionally
reduced to only 500 lines because of overlap. Unfortunately, film recorder
manufacturers do not provide information on spot size or overlap.
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