Simply Stated — Working with Digital Images
November 22nd, 1999 |
By Rob Stevenson, stevenson@macsimple.com Contributing Columnist |
The field of digital imaging is changing at least as rapidly as the computer technology on which it is based. Only a few years ago, it was not a serious, cost-effective replacement, perhaps not even an adjunct, to the use of regular silver-based film for professional or business imaging. Now it is. So today I’m going to offer a brief, and completely non-controversial, survey of the field.
A company I’m involved with publishes fine-art images on greeting cards and similar products. We work from slides provided by the artists, proceeding digitally from there. I thought I’d share what we’ve learned about the process, heavily condensed to fit in one column. Using digital images involves three basic processes: image capture, storage, and reproduction. Each of these can be accomplished in various ways.
Image capture
Digital images can be captured directly in a camera. There are more than 100 models from which to choose, at many price points. The camera can be all digital, or the image capture can occur in a digital add-on to a traditional 35mm or larger film camera.
Images can be created first in some traditional medium such as paint, which can then be photographed and scanned to create a digital reproduction of the original. If small enough, prints and flat art work can be directly scanned in a flat bed scanner. Images can also be created directly in the computer using graphics programs. No matter how it has been created, subsequent image storage and processing is much the same.
Image capture quality is defined by the number of pixels per inch, the optical density range of the capture device and the number of bits per colour being captured. As usual in the computer world, more of any of these is better. Some capture devices interpolate to produce more pixels per inch than they read, but this may not be a good thing. The software controlling the scanning process can also have an effect on subsequent image quality.
Cost of image capture can range from essentially zero for an image taken in a point and shoot digital camera (ignoring its amortized cost) to $20 or more for a professionally scanned transparency.
Storage
Images are large. For comparison, a long, complex word processing document may require something like 100 Kb (Kilobytes) of space on a hard drive. A not very large or complex image can take 10 Mb (Megabytes) or 100 times as much room on the drive. Obviously, one could only store 1/100 of the number of image files on the same drive. Rough as it is, that is a useful ratio to keep in mind.
Images can be stored on hard drives, the cost of which has come down remarkably in recent years. But most hard drives are not readily transportable. Image storage commonly utilizes one of several competing removable drive formats: Syquest, Jaz, Zip or CD-ROM. Coming up fast, and likely to replace one or more of these, is the DVD format. Using these removable devices allows images to be sent out for use by printers or designers, and to be moved off site for secure, redundant, long term storage.
You will eventually want to use software for managing your image storage. To start with it is easiest to store the images “manually”. That is, you handle them a file at a time, naming them as you wish, and storing them where you wish. You would probably keep a database file, perhaps containing small thumbnails of your images, as a reference to the location and names of your larger image files. You often get a simple version of such software free with your scanner or digital camera.
More capable image database software is available which you may want to look into it as your needs grow. It can be expensive. I’ve seen a demo of one such product, called Cumulus, which costs US$2500. Others are available for from two to five times that price.
Storage costs are difficult to determine without knowing actual file sizes, but is in the range of 15� to $2 per image. It should be the least expensive element in the equation.
While we�re on the topic of image size, the effects of moving large images around on a network should not be ignored. This can use up scarce network resources. You may want to consider upgrading your network cards to 100Base-T to increase the speed of file transfers.
Reproduction
Images may be reproduced on-line, as in digital catalogs on the internet. Small, low-resolution images can be used this way, because they are seen on computer screens. The original image may have 1000 or more pixels per inch, but most screens can�t display more than 75�90 pixels per inch. These smaller versions of your images may reasonably be stored in a database such as FileMaker Pro.
You’ll want to print your images for a variety of purposes. Small, low quality prints may be created for temporary use on regular ink-jet printers or the new photo printers, many of which can connect directly to a digital camera without need of a computer. Larger, near-professional-quality images may be produced in house on ink jet or colour laser printers. And of course your images may be professionally printed.
Reproduction brings up a technical issue to consider. Designers and printers expect to work with CMYK images. That stands for the four printing ink colours: Cyan, Magenta, Yellow and blacK. Simple image creation tools, like digital cameras and all but the most expensive scanners, create images in RGB format. This Red, Green, Blue format is suitable for viewing on screen, and for simple, snapshot quality printing. It is not suitable for professional reproduction. Because any conversion process can reduce the quality of the image, it’s best to start with a CMYK image if at all possible, and convert it to other formats as needed.
Cost of reproduction can vary considerably, from a low of $2 per image for an ink-jet print (counting the cost of ink and appropriate paper) to a high of $200 or more for a professional print from a professionally scanned slide.
Purchase advice
The low end of the price scale is occupied by equipment that anyone can own. The high end is not. For example, a low end slide scanner can be an add-on to a flat bed scanner, the two together costing as little as $300. The mid-range slide scanner costs from $800 to $2000. A high end one can cost from $20,000 to $75,000 to buy, and requires a trained and well-paid operator to use.
Similarly, the low end printer is a readily available ink-jet costing from $150 to $1000. The mid-range would be a colour laser printer costing several thousand dollars. And the high end goes all the way from a high-res proofing ink jet for $10,000 to the printing industry�s sheet-fed and offset presses costing many hundreds of thousands of dollars.
For high quality input and output it is best to depend on the professional image service bureaus and printers. The cost per image seems high, but remember the equipment costs are being amortized by them. Expect to purchase the low and mid range equipment.
Since you’ll likely need an inexpensive ink jet printer no matter how large or small the budget, you could start with that, professionally scan some slides of representative images, and experiment a little. Then work up into the more expensive items from there. As we�ve learned from recent years experience, waiting just means you’ll get more for less.
With that happy thought, I’ll leave you until next week.
