Digital Workflow

Digital Imaging typically involves the following steps:

1. ACQUISITION. An image is scanned, electronically photographed or digitally rendered into the random access memory of a computer.

2. ON-LINE STORAGE. The acquired image is stored for further use in an accessible but secure location, preferably a departmental file-server. Ideally, no local copies are maintained elsewhere. By maintaining a single working copy of the image file in a central location, the confusion ensuing from a proliferation of derivative files in different locations is avoided. Only the owner or her designee can access the stored image, and nightly backup of the server guards against catastrophic loss.

3. PROCESSING. The image is adjusted for color balance, noise and sharpness, size, cropping, resolution, etc. The adjusted image remains on the file server in its original location.

4. COMPOSITION. If necessary, the image is annotated or composited with other information. This may include text labels, markers such as arrows or scale bars, and/or other images. The document containing the composed or annotated images is saved under a new name on the file server, leaving the constituent originals intact for future use.

5. ENCAPSULATION AND OUTPUT. The final document is either sent directly to an on-line printer or saved as a Postscript file for later output via any PostScript® device.

6. ARCHIVING. If there is no further immediate need for the image and related files, they are transferred from on-line storage to durable, inexpensive and carefully cataloged off-line media such as CD-ROM discs. This ensures future availability of the archived files and permits the system's on-line storage capacity to be recycled.

Digital Images

Because most computer monitors and printers are unable to produce smooth lines, they approximate them by drawing tiny squares of color called

pixels (Picture ELements) of the smallest size feasible. This means that every digital image you are likely to encounter will be composed of pixels. A computer monitor might be able to draw 75 of these dots per inch (DPI) on its screen, while a standard B&W laser printer might manage 300 or 600 DPI on paper.

Bitmaps

Many images are simple arrays of pixels. This icon from Netscape® consists of 1024 pixels in a 32 by 32 matrix. Such an image has an inherent resolution. No matter how big or small the display of this image, it will always contain 1024 pixels. Stretched out over a large enough area, the pixels become conspicuous. Images such as the Netscape Icon, scanned photographs and frames of digitized video are composed entirely of pixels in a rectangular array, and are referred to as bitmaps. These image are stored as a series of pixel color-values recorded at regular horizontal and vertical intervals. TIFF and GIF are common bitmap types.

Image Resolution

Objects

Even images composed purely of geometrically defined lines and shapes having no inherent resolution can be experienced only through the inevitable mesh of pixels generated by a monitor or printer. Text falls into this category, as well as diagrams created in Deneba Canvas®, Adobe Illustrator® or similar programs. These will be drawn at the output resolution of whatever display device is being used at the moment.

Output Resolution

The display resolution of output devices will always determine the way you interact with your images:

CRT Displays

In Adobe Photoshop®, the relationship between image resolution and screen resolution is explicitly stated in the header of every image window. The legend 1:1, for example, indicates that every pixel in the image file is allocated a single corresponding pixel on the display monitor. Because computer monitors typically generate pixels that are larger than those used to originally capture images, the images as a whole are much larger on the display screen than they are when printed out on a device that generates smaller pixels, such as a laser printer. A legend of 1:2 indicates that Photoshop is displaying the information in the image at one-half of its actual density, while 2:1 would indicate that the image is being displayed at twice its actual density. Obviously, since we are discussing two-dimensional images, a pixel displayed at 2:1 will be represented by four screen pixels. The methods by which programs display images at resolutions of less than 1:1 can be quite complex, and the quality of the displayed images can vary considerably between programs. Because of this, and because of the inevitable elision of image content, critical judgments about such things as sharpness, noise and detail should be made at a display resolution of 1:1, even if this entails evaluating the image in portions.

Hardcopy

With the exception of images destined exclusively for electronic publication, the final product of most digital imaging is hardcopy output. This generally entails using ink, solid toner or light to inscribe an image onto film or paper. Failure to anticipate from the outset the peculiarities of the specific technology which will used to do this, and the circumstances under which the final product will be viewed will greatly complicate the entire process. The following criteria should be considered before the acquisition phase, if possible:

What are the content peculiarities of the image file?

What is the anticipated medium of the final output?

What is the anticipated size of the final output?

What is the anticipated resolution of the output device?

What are anticipated viewing conditions of the final output?