Digital photography - technology and technique

Having been involved in photography as a serious amateur for over 40 years now, and with computers professionally for about 35 of those years, it is not surprising that I recently took the plunge and started my personal exploration of the world of digital photography as well. I would like to share some thoughts on this experience with fellow PSA members, not from the viewpoint of instruction in digital photography, but rather with the goal of providing an idea of what is involved, especially from the standpoint of the amateur photographer. Sadly, the popular photographic literature at this writing has not really addressed this issue. Except for Shutterbug, which runs monthly columns on techniques, hardware, and software, all the rest do is show some results which, although always intriguing, does not answer the question, "Do I take the plunge and, if so, what am I getting into?" Although prints certainly are also a part of digital photography, in order that this article be kept to a reasonable length it will be assumed that any image in question originates from a 35mm color negative or positive, and that the final image is a 35mm color slide.

The basic notion behind digital photography involves something known as a "pixel" (a word constructed from the words "picture" and "element"). A pixel is the smallest piece of information viewable on a computer monitor. If you look at a monitor (or TV screen), you will notice that the image is made up of what appears to be numerous dots. This is deceiving since, in actuality, these "dots" are not circular, but square. Each dot is a pixel and has a color. The number of pixels that can be displayed is called "screen resolution," and the number of colors is called "color depth." The greater the number of pixels, the more detailed the image; the greater the number of colors, the more realistic the image. As you might expect, the more pixels and/or the more colors, the greater the price of the computer system.

Digital photography involves three steps: (1) Getting the image into the computer; (2) Processing or manipulating the image in the computer; and (3) Getting the image out of the computer. Traditionally, items 1 and 3 have been the most expensive of the three, far beyond the budgets of the typical photographer even if he or she already possessed a home computer. This situation is rapidly changing, however, and, with the advent of the Kodak Photo CD, at least some elements of digital photography now are practicable for a significant number of photographers.

The process of getting an image into a computer is known as "scanning." A scanner takes a photographic image, which is of a continuous tonality, and breaks it down into pixels. The pixel information is then stored digitally in a computer, subsequently to be manipulated by the photographer using a suitable software program. Since film doesn't have pixels, the question arises: "How many pixels and how many pixel colors does it take for the scanned image to look pretty much like the original photographic image?" Although there is some uncertainty to the answer since it depends upon the quality of the film and lenses used in making the original image, for a 35mm image it would take about 11 million pixels and 16 million colors (in computer parlance, 16 million colors is known as "24-bit color" since [2sup.24] = 16,772,216). This means there would have to be about 4096 pixels horizontally and 2731 vertically. For convenience, let's agree to refer to resolutions solely by the number of horizontal pixels since the horizontal-to-vertical ratio of a 35mm image is a constant.

Film scanners (as opposed to the flatbed scanners commonly used for scanning opaque materials such as photographs and images from magazines and books) that can scan at 4096 pixels are available for the home computer, but the cost is prohibitive. Our requirement assumed that ISO 100 film would look like ISO 100 film when scanned. How about relaxing the requirement to having it look like ISO 200? Now there would have to be only 2048 pixels horizontally. At this writing, film scanners that can supply this level of resolution at 24-bit color are available for about $1800 street price. If the requirement is relaxed a bit more, film scanners which can scan at a rate of 1832 pixels at 24-bit color can be had at a street price of under $1500. In most cases, however, this is still more than the cost of most home computers.

Fortunately, Kodak has solved the financial problem for many of us in the form of the Kodak Photo CD (PCD). In the area in which I live, for about $1.80/ slide (with a minimum of 10 slides plus a $3 processing charge) Kodalux will scan your slides onto a CD ROM, each slide being available to you at five different resolutions (and 24-bit color) as follows:

  Base/16   192
  Base/4    384
  Base      768
  Base*4    1526
  Base*16   3072

Note that although the highest resolution (3072) is not quite equal to the original film resolution, it comes quite close. (Kodak has recently introduced the Pro Kodak Photo CD which provides resolutions of Base*64 or 6144 horizontal pixels, but images scanned in this format are expensive and require special software to read and manipulate.)

Before rejoicing over the Kodak solution, however, let's take a look at the relationship between pixel-load and computer-load. The accompanying table shows several of these relationships, using my present home computer and a test PCD image. This computer configuration (particularly the fast, 66 MHz chip and the fast video board that can display 24-bit color at a resolution of 800 x 600 pixels) is typical of "graphic" computers, i.e., those capable of handling complex drawings and other artwork. A true "imaging" computer would have greatly increased random-access memory (RAM) - (128 mb or more) - and and a video board that can display 24-bit color at a resolution of 1024 x 768 pixels. This upgrade, however, would cost a minimum of $7,000 (mostly because of the cost of the additional RAM ) .

Only the top three resolutions provided by the PCD are shown, plus two others indicated as "resampled." (These resampled images are not read from the PCD directly; they are obtained by using the imaging software to reduce - by "throwing away" information - the image from the next highest resolution read from the CD.) The first thing the table tells us is that high resolutions take a long time to load and process if computer memory is limited. At a resolution of horizontal 3072 pixels, the test PCD image took 9 minutes and 36 seconds merely to load into my computer. Since the image file required 18 mb of memory and my computer only has 16 mb, there was considerable swapping of parts of the image between memory and hard disk as manipulations are made on the image. Consequently, on large images the manipulations take a long time.

One of the very common manipulations is to sharpen the image. This takes 5 minutes on this file (although, as indicated in the table, it can be reduced by using a special type of computer board, costing about $400, called a "Digital Signal Processor"). When memory is limited, one can be at the computer for hours on a file this large when adjustments are made to hue, saturation, contrast, brightness, and sharpness, not to mention cropping, removing hotspots and other "cloning" techniques, and any creative image alterations such as replacing parts of an image with parts from another. Computer memory can, of course, be increased but the going rate for RAM at this time is about $50 to $60/mb. Upgrading my "graphics" computer from 16 to 32 mb of RAM would cost, therefore, at least $800.

Although the image can be saved to disk in a format that requires considerably less space than the memory requirements, the resultant 10.51 mb still consumes significant hard disk resources. Even though one of the two 245 mb hard disks on this computer is dedicated to nothing but image storage, only 23 such images can be saved on it.

How does one get the image out of the computer? This is accomplished with a device known as a "film recorder." A flim recorder consists of a cathode ray tube (a sort of tiny computer screen capable of displaying many pixels) attached to a camera back. Although the recorder produces a continuous tone image on each pixel written to the slide film, the pixels can be seen under magnification as dots. The better ones can handle a greater number of pixels and thus produce a smaller spot size, i.e., the size of the pixel on the cathode ray tube. (By the way, since what you see on the screen will definitely not be what the final output looks like, preparing images for film recording requires considerable training, experience, and skill.) Although prices are coming down, film recorders are considerably more expensive than film scanners; 4096-pixel resolution recorders have a street price between $5000 and 5500, with 2048-pixel resolution recorders costing about $4000. (Statistics on 2048-pixel images can be found in the table.) For the amateur photographer, these costs are still much too high. At the present, the only answer is to send the computer file containing the image to a service bureau which has the necessary equipment.

There are two problems with this solution, however. One is cost, since charges can vary from $5 to $25 or more per slide depending upon the image size. The other is that the large size of files containing images at these resolutions does not permit sending an ordinary computer disk to the service bureau; the usual 3-1/2" disk only has 1.44 mb of storage, and saving even a base*4 file (a resolution of 1536) in the TIF format using compression requires 2.45 mb. It is true that there are other compression methods available but, unlike TIF compression, they involve some loss of data. This means that, in order to conserve space on the disk, some image quality is sacrificed. Furthermore, very large files cannot be compressed sufficiently to fit on a 31/2" disk. Thus you will have to add a removable disk drive of high capacity to your computer, e.g., a SyQuest drive (the type commonly accepted by service bureaus) of 44 or 88 mb capacity. This will cost about $450, with another $65 to $100 for each disk (you do get your disk back from the service bureau, however!).

The conclusion to be drawn at this point is that digital photography, if it is to approximate the current resolution of photographic film, consumes significant computer resources (and thus a great deal of money) in addition to the considerable time you must spend in front of your computer doing the manipulations. Although the picture is changing in that (a) prices are being lowered for scanners, computer systems and recorders, and (b) computers are becoming faster and peripherals are becoming available to speed up certain imaging manipulations (digital signal processing boards, for example, long available to Macintosh computers have just become available for PC's), it will still be a while before digital photography becomes a practical matter, in the economic sense, for the average amateur.

Photographing the computer screen is one area, however, where digital imaging is practical right now for the amateur, assuming that he or she has a home computer of fairly recent vintage and moderately respectable credentials, i.e., one running Windows 3.1 with at least 8 mb of RAM, a good monitor and video card, and a CD ROM drive. (The imaging software itself is not all that expensive.) In other words, a "graphics" computer is ideal. The process is as follows:

(1) Import the image from a PCD at either Base (768 pixels) or, better still, Base*4 (i.e., 1536 pixels) combined with resampling down to 1024 pixels;

(2) Photograph the screen at a resolution of either 800 x 600 at 24-bit minimum color depth, or 1024 x 768 at 15-bit (32,768 colors) minimum color depth, depending upon the resolution selected in step 1.

This will produce slides that, although not of general competition quality, can be used (a) in "creative slide" competition, and (b) for producing slide shows in which the quality of the projected slides is not as critical. Video cards that can produce these resolutions are reasonable in cost (around $400), and most monitors on the market today can accommodate this kind of card.

Note: I am often asked about photographing computer screens, and people are a bit surprised to learn that it is a bit more complex than has been suggested by many writers. For one thing, computer monitors are calibrated for 9000 [degrees] Kelvin; this is much too blue for daylight film so a color correction filter must be used (I use a Kenko TV conversion filter which takes it down to about 6000' Kelvin). Also, monitor manufacturers vary in how they optimize monitor variables. My monitor manufacturer (Nanao), for example, sacrifices brightness for certain other qualities, such as contrast, so I cannot tell anyone precisely what exposure to use to produce satisfactory results on their system. Furthermore, one photographs the screen in darkness, whereas the image manipulation takes place in ambient room light. If the monitor is calibrated for room light, it will be too bright for photographing. For photographing, I turn the brightness way down so that blacks are truly black and not gray. This, of course, affects the exposure. This said, using ISO 100 Fujichrome daylight film, a 60mm macro lens, and a 15" (nominal) computer screen, my exposure is 1/2 second at f5.6 set on the lens. (Since this is close-up photography, the effective aperture is approximately f8.)

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