[Ed. note: This article was originally published on the Windows edition of Nautilus, Vol. 2-13 (December 23, 1992).]
The Big Picture
Nautilus subscribers have marveled at the photography appearing in each issue for many months now. If you're curious about how an image gets into a computer in the first place, read on!
First, some basics. The screen you're looking at contains thousands of small dots called picture elements, or pixels for short. The dot over the letter "i" is one pixel big (on most displays--more on that later). Each pixel can assume one of 16 colors (more if you are using a special super VGA display setup). Since the dots are so small, ordering them in patterns can fool the eye into perceiving colors, like a shade of orange that really is a checkerboard pattern of red and yellow (for instance). Viewed from a distance (even if the distance is a few inches), these checkerboard ("dither") patterns look like colors outside the range of the basic 16 (or basic 256) colors normally available on screen.
Taking 16 colors and arranging them in 2x2 checkerboard patterns results in 1820 unique combinations. This yields a larger perceived color selection than just the basic 16. In a 3x3 pattern, there are 11,440 combinations. Yet as the size of the checkerboard grows, the actual resolution (perceived pixels as opposed to individual pixels) shrinks. Assuming your screen is a standard 640x480 resolution, using a 2x2 pixel checkerboard gives only 320x240 locations on the screen to put the 2x2 groups. Using this method tends to make photographic images appear grainy, coarse, mosaic-like. Also, because you do not always have a choice on exactly which 16 colors make up the picture (due to operating system limitations), a picture rendered with a 16-color palette can look "spotty." The perfect colors to produce the desired effect simply aren't available.
When you increase the resolution of your display (800x600 or higher), you can also increase the size of the dither (3x3) without suffering too much loss. High resolution and large color palettes (1024x768 with 256 colors for instance) provide better resources for picture reproduction. Today, 24-bit color display adapters provide the closest to exact photographic reproduction popularly available.
In addition, checkerboard (also known as ordered pattern) dithering is the simplest and, in many cases, least efficient. Floyd-Steinberg, Bayer, Stucki, and other strange names abound in the field of picture rendering.
Say Cheese!
Photographic images also have pixels, more commonly called the "grain" of the film. A special thing about film grain is it's not arranged into neat rows and columns. If pixels on a video screen could be arbitrarily spaced, image quality could again improve.
There is a smallest detail on film beyond which you cannot accurately record an image. If you've ever seen a poster-size enlargement, you'll see the grain of the original image. The larger the area of film you have to hold an image, the larger you can blow it up before noticing its grain. This is why 70mm movie film is popular. For cameras, where the resultant image is meant to fit in an album (as opposed to a movie screen), 35mm is sufficient.
Once you have an image (say a photographic print), to represent it on a video screen requires that the image be broken up into ordered pixels, arranged in a particular dot spacing (say 100 per inch in either direction). A 4x5" print would then become 400x500 pixels big when converted to a video image. Assuming the picture is in "landscape" mode (wide orientation), it would fit comfortably on a 640x480 pixel screen.
There are many methods of translating a printed image to pixel information. The most popular is called scanning. A device moves (or is moved) over the image, looking at a thin slice of the picture and converting it into a sequence of pixel values for each "row." As the scanning progresses, additional rows add to the image forming in memory.
The memory image often contains more color information than can be represented on the screen, so the next step in the process is to convert it into a dither pattern with whatever palette (256 or even 16 colors) is available. Depending on the software used, an image may be edited, details added or removed, colors adjusted, special effects performed, and so forth. "Digital Image Processing" is a buzzword used today to describe all the special conversion, editing, and adjustments that one can perform on scanned images today.
Digital Image Processing does not require you to own a scanner. If you are content to use existing pictures (such as those found on Nautilus discs), you may use a Digital Image Processing program to do things that even the best photographic studio cannot produce. Scanners come with their own software for this purpose, but you can purchase the same programs by themselves without the scanner. Micrographx Picture Publisher and Adobe Photoshop are but two examples. These can read the TIF files you typically find on the Nautilus discs.
Scanners have come down in price: a good color scanner costs under $600, complete with Digital Image Processing software.
If you already own a camcorder, chances are you can attach it to a video digitizer, which takes the TV signal and converts the scan lines from the camera into pixel rows. Unfortunately, these "digitizer" boards are about as pricey as a hand-held scanner, and the image quality seldom approaches what is possible with higher resolution scanning. The benefit is motion. Some digitizer boards can work with software that can create the AVI files you saw on the Nautilus disc with Video for Windows.
Full-motion video with synchronized sound is a whole can of worms in itself, and best left to another article dedicated to exploring the details.
More About Screens
Scanned images begin at a certain size (the size of the original print). Because many PC users have the ability to change the resolution of their displays, one inch of video screen can contain more pixels at one resolution than at another. It's best to match screen resolution to scan resolution, but this is seldom practical. Enter DIB, or Device Independent Bitmaps. A scanned image contains a number of dots per inch (the input resolution). A screen contains some other number of dots per inch (output resolution). Windows permits a translation scheme from one to the other--DIB format files. Most images appearing on Nautilus today are DIB files, which appear as close to the original as possible (given the limitations of screen resolution and color). Windows 3.1 applies similar technology to fonts, enlarging or shrinking letters to fit the screen (in an attempt to maintain the same size and spacing of words). Therefore, the dot over the letter "i" on a very high resolution screen could contain more than one pixel. The number of dots used in a dither pattern may also adjust up or down in an attempt to render it in the size desired, taking the resolution of the display into consideration.
Cheaper Scanning?
If you're thinking "there must be a better way" when considering getting an image into your computer, you're right. Chances are you already own or can upgrade the equipment you now own to do exactly this inexpensively and easily. This is a new technology recently advertised and promoted by Kodak, called Photo CD. Nautilus subscribers already own a CD-ROM drive, and many (I expect) own a camera. Right now, you can take a roll of film to an authorized developer and have them perform Kodalux processing. This develops film onto a special CD-ROM called a Photo CD. You get back your negatives (or slides) and a CD-ROM with your images recorded on it--in 5 sizes (from thumbnail to poster size) and in 24-bit color. Then, by using access software (a one-time investment of $39 from Kodak), you can view your pictures on your computer screen and convert them into 256 (or 16) color images in a number of formats (including TIF). This makes it rather simple to take a photo and incorporate it into a document, or simply send it on diskette (or by modem) to friends. As with all computer images, you can print it (even in color), if you have the appropriate printer.
I have personally developed a 24-exposure roll of film onto a Photo CD and have viewed the images in 24-bit color on my computer. (I have the benefit of a high resolution, "true" color display adapter.) The development and transfer process cost me about $16, complete with new CD-ROM disc. I expect to develop additional rolls of film onto this same disc for much less (as the disc itself contains some gold and is therefore a little pricey).
What's done when you send a roll of film for Kodalux processing is pretty much what happens when you have it developed a conventional way--with a special step added. Once your negatives (or slides) are developed, they are put into a machine that scans them (using 5 different resolutions) and records the images onto a CD-ROM disc. The disc is a special "write once" kind of CD-ROM, and most people can only read them. CD-ROM drives that can record on this kind of media still cost thousands of dollars.
Is there a catch to using Photo CD?
Yes, many--depending on how early you got your CD-ROM drive, and how powerful your computer is.
Because 24-bit, high resolution images take a lot of space, and because a Photo CD may contain more than just images, "extended architecture" CD-ROM features are required to decode the picture data (as well as any other data may be added to it later). This ability (in the CD-ROM drive and its driver software) is called "Photo CD access ability," or "Single Session Photo CD capability" by the industry. Typically, drives that have (or can be made to support) CD-ROM/XA, Mode 2, Form 2 operation can read a Photo CD. Many of the new drives made by IBM, Toshiba, Texel, NEC, and others either are Photo CD capable or can be modified to be so. The only drive that I've (in person) seen read a Photo CD is a Texel DM-5024. Their DM-3024 (an internal version of the same unit) should also work. I've heard from people that the NEC CDR-74 and 84 also work, providing one gets a very recent version of the driver software.
Kodak has an information center that can usually tell you whether your CD-ROM drive can read a Photo CD, or could be upgraded to do so. Their number (inside the United States) is (800)242-2424, extension 53. This same number is where you can purchase Photo CD access software, as well as get information on where you can find Kodalux processing near you.
More catches!
Now that I've developed 24 images onto a Photo CD, if I choose to add images to this disc, most Photo CD readers will not recognize there being any more than 24 images on the disc. This is because the Photo CD appears to end after the first development "session." When you return the disc and have another set of images added, this creates a subsequent session on the disc--in a kind of "no-man's" land where most CD-ROM drives fear to read. Only if you have a multisession Photo CD reader can you read subsequent development sessions. The Texel DM-5024 may be upgraded to multisession. I've heard rumor that it's inexpensive--perhaps $20, but you need to return it to the factory to have it done. It's more complicated than just moving a jumper or changing a CONFIG.SYS file. Once this modification is made, the hardware is ready for multisession, but still the software (whatever driver appears in CONFIG.SYS for the CD-ROM drive) needs an update too. Seems Kodak really gave a shot in the arm to the upgrade profession with multisession capability!
Judging from the price of Kodalux processing (which should continue to drop as more and more labs offer this ability), Photo CD should become more and more important and commonplace in the months to come. Photographs on Photo CD are already about the price of "instant" pictures--making me wonder how long it will be until there are one-hour Photo CD shops. (The bulk of a Photo CD maker makes me skeptical about instant cameras that record straight onto Photo CD becoming reality.)
Photo CDs can contain images taken from negatives or slides (either fresh or previously developed film). Sometime next year, the ability to transfer prints (even pictures cut out of magazines or books) onto disc should be available.
For some people, Photo CD may be less expensive than buying a scanner or digitizer. Others may find their CD-ROM drives cannot read (nor be upgraded to read) Photo CD, and therefore using Photo CD may cost hundreds (considering the price of Photo CD capable drives today).
The means to put an image into your computer and onto your screen have been greatly expanded (and made a lot more affordable) just in the past year. I imagine by this same time next year, hundreds more people will be using and editing their own images than ever before.
