Before going into the details of Photo CDs on the Web, let us describe the process of digitization of photographs, which Photo CD technology is based upon.
We start with the widespread 35mm camera. A camera exposes an image on sensitized film. When exposed properly, photochemical changes occur in the photographic film. Later special developing and processing techniques reproduce the recorded image as a photographic negative, from which prints can be made. Color-reversal films produce positive images that can be mounted as slides.
Digital Imaging makes use of the fact that films are made of extremely fine granular chemicals. (Kodak, Glass Plates) Using digitizing equipment, a film-based photograph can be scanned, digitized to 18 megapixels (18 million picture elements), stored, and can then be played back for television viewing. For comparison, the average consumer camcorder records approximately 250,000 pixels per frame. One storage option is Compact Disks which can be accessed via CD players that play both Photo CDs and audio CDs. They can also be viewed and manipulated on personal computers, transmitted via telephone lines, and printed. Thermal printers can print images, from a Photo CD, that approach photographic quality. In general, Photo CDs serve as a high quality storage medium for photographs in much the same manner as an audio Compact Disc stores recorded music. As a rule of thumb, Photo CDs can hold up to 100 photographs. Because they originated on film, each picture has a much higher resolution than images recorded electronically.
Photo CD is a revolutionary new tool for office computing and desktop publishing, making it possible for the first time to incorporate continuous tone images into computing environments. (Kodak, Photo CD Menu) Kodak has created a new worldwide standard for reproducing color in digital form and has developed software to provide consistent color across computer platforms and peripherals. This standard has been supported by the industry's leading computer equipment and software manufacturers.
In addition to Photo CD, Kodak has introduced a number of
other hybrid products that combine the
high quality of silver halide imaging with the
convenience of electronic manipulation.
(Kodak, Glass Plates)
26.2.2 Photo CD - Usability
Computer users have been quick to take advantage of digital imaging
technology, helping to drive acceptance of the Photo CD format as a
computer industry standard -- supported by hardware operating systems,
software applications and CD-ROM drives. Because drive manufacturers
adopted the multi-session recording standard, every multi-session
CD-ROM XA drive is capable of playing Photo CD discs. This has created
an installed base of tens of millions of Photo CD-compatible drives.
Once a disc has been loaded into a drive, additional software is
needed to read and display Photo CD images. Many hardware
manufacturers offer this capability as a built-in feature of their
operating systems, allowing users to incorporate Photo CD images
directly into any software application. They include Apple Computer's
QUICKTIME extension, the IRIX operating system from Silicon Graphics
and Sun Microsystems' SOLARIS. IBM's OS 2/WARP platform can read and
write Photo CD discs, and IBM supports Photo CD technology in its AIX
operating system (which runs on RISC System/6000 workstations) through
Ultimedia Services, an optional package of multimedia tools.
(Kodak, Digital Imaging)
Although Photo CD technology can benefit almost anyone who wants or needs to use pictures, there are four leading application areas: printing and publishing, presentations and training, image archiving and distribution, and desktop color compound documents. (Kodak, Photo CD Products)
Perhaps the most distinctive feature of Photo CD color encoding is that it allows each output device (such as a home player, a computer monitor, or a thermal printer) to produce images from any Photo CD data file, regardless of the type of input imaging medium that was scanned to produce that file, such as negatives and positives. This feature results from the use of a proprietary input encoding technique that achieves input compatibility of Photo CD images scanned from a variety of different sources. (Kodak, Technical Information)
Without input compatibility, each output device requires multiple output data-processing paths (transforms) in order to properly produce images encoded from different types of inputs. With Photo CDs unique input compatibility, the data-processing path for each output device is independent of the original source of the Photo CD encoded image. Each output device therefore requires only a single transform to produce output images from any image encoded on any Photo CD disk.
Photo CD input compatibility allows for the cutting-and-pasting of elements of Photo CD images that originated from different types of input media into composite images. For example, portions of images scanned from negatives can be readily edited together with images scanned from transparencies to form homogeneous-appearing composites. A composite image can then be sent to any output device, where the entire image will then be reproduced in a way that has been optimized for that particular device. In addition, input compatibility allows all images to be adjusted and manipulated, during and after encoding, by the use of a common set of application software tools.
The color-encoding basis of the Photo CD system is the Reference Image-Capturing Device. All Photo CD images, regardless of their actual mode of capture, can be thought of as having been captured and encoded by the Reference Image-Capturing Device. This conceptual device provides a consistent calorimetric definition for the Photo CD system. Moreover, the concept of this Reference Image-Capturing Device provides the basis for achieving compatibility among the various types of media that are input to the Photo CD system. Output values from the reference device then go directly to the Photo YCC color encoding (we will discuss Photo YCC in more detail in the next section) and are processed on the Photo CD Imaging Workstation (PIW) to produce values corresponding to those produced by the reference device. Compatibility is therefore achieved by the transformation of scanned image data from each input medium to a common meaning and a common numerical encoding. (Kodak, Technical Information)
One of the unique features that results, in part, from input compatibility is the flexibility that is created for output. Photo CD image data can be transformed in the output process to correspond to either of the above calorimetric objectives, or to virtually any other desired color-reproduction objective. But it is important that, during the encoding process, the basic original-scene-colorimetry interpretation is fundamentally maintained in order to ensure that all recorded images are consistent and compatible with all other Photo CD images.
In the next section we will look at how Photo CD makes use of the WWW, in particular how it is achieved and how the Web opens a whole new market for this technology.
Dan Haim
<haim@vt.edu>
Last modified: Sun Dec 15 17:17:52 EST 1996