Also Known As: Photo CD
| Type | Bitmap |
| Colors | 24-bit |
| Compression | Proprietary |
| Maximum Image Size | 2048x3072 |
| Multiple Images Per File | No |
| Numerical Format | NA |
| Originator | Eastman Kodak |
| Platform | All |
| Supporting Applications | Photo CD Access, Shoebox, Photoshop, others |
| See Also | None |
Usage
Static data storage of multi-resolution deep-pixel images.
Comments
Kodak will not divulge information on the format that would enable developers to directly access the image data.
Sample images are available for this format.
Photo CD is actually the name of a CD-ROM-based storage and retrieval system from Eastman Kodak. Most people in the development community use the name Photo CD to refer to the files associated with the system, however, and we will conform to this usage.
Contents:
File Organization
File Details
For Further Information
A Photo CD CD-ROM is intended for the storage of conventional film-based photographic images which have been converted to digital form, using a slide or flatbed scanner, for instance. This is apparently part of Kodak's strategy for the product: to serve as an adjunct to their conventional film business. There are no technical restrictions on the source of the data, however.
Unfortunately, we cannot describe the Kodak Photo CD format in any detail because Kodak will not divulge the details of the format, and, in fact, has threatened legal action to those who would seek to reverse-engineer the product. This decision on the part of Kodak has enraged members of the development community who have an interest in the future of imaging technology. Cooler heads see Photo CD as a transitional technology. Our own opinion is that a large company with a sufficient presence in the market and a long-term view could have used a system like Photo CD as a way of capturing a major share of the disc-based multimedia market. However, Kodak seems to have taken the more conservative course of protecting their traditional film-based business.
Kodak does, however, sell a shrink-wrapped Photo CD development kit for a reasonable fee, which provides an API of sufficient richness for almost any developer need. At the time of this writing, there are Microsoft Windows, Macintosh, and UNIX versions of the toolkit available. Obviously, developers on other platforms are out of luck, unless Kodak sees fit to accommodate their needs. Toolkits are closely coupled to the platform supported.
As a result of the situation we have described, we are obviously able in this article to provide only information about the Photo CD system and format that is publicly available from Kodak.
In the Kodak Photo CD environment, groups of images and associated information written at one time is called a session. The original Photo CD specification called for hardware that supported a single session per disc. Later versions of the Photo CD system allow multiple sessions per disc, which requires special hardware, firmware revisions, or a combination of both to read. As a consequence of this, many older CD-ROM drives will not read multi-session Photo CD discs, so you might make sure that yours does before you get involved with the Photo CD system.
Taking advantage of the storage capacity of CD-ROMs (more than 600 megabytes), images are stored on disc at multiple resolutions, in an arrangement called pyramid encoding. This accomplishes the same thing as the common strategy of storing a "postage stamp," or reduced version of the main image in the same file, albeit carried to a logical extreme. At the time of this writing, six resolutions are normally stored for each image:
Base Over 64 |
64x96 |
Base Over 16 |
128x192 |
Base Over 4 |
256x384 |
Base |
512x768 |
Base Times 4 |
1024x1536 |
Base Times 16 |
2048x3072 |
Another version of the Photo CD product, called Photo CD Pro, may contain higher resolutions, including:
Base Times 16 |
2048x3072 |
Multiple versions of the image are grouped into a file that Kodak calls an Image Pac. A copy of at least one of the two lowest-resolution versions of the image in the Image Pac in the current sessions is stored in another file called the Overview Pac. These are used for the display of postage stamp images, which might be used by an application for quick display of the images in the Image Pac, for selection purposes, perhaps.
In the Kodak Photo CD format, Image data is compressed using a proprietary algorithm. Data is stored in what Kodak calls PhotoYCC format. The developer toolkit delivers color in several formats, depending on the platform. These include 256-level gray-scale and various palette-based formats, in addition to 24-bit YCC and RGB.
In the 24-bit YCC format, 24 bits of data per pixel are distributed among three color components, called Y (luminance information), C1, and C2 (two chrominance channels). Each channel occupies eight bits of data. Although the YCC format has some advantages, most developers choose RGB as the preferred model in which they want the toolkit to deliver the image data.
More details about the Photo CD format are available in descriptive documentation from Kodak marketing sources and in the Kodak Photo CD Access Developer Toolkit for your platform, which contains the following:
For information about obtaining these, contact:
Eastman Kodak Corporation
343 State Street
Rochester, NY 14650
Voice: 800-242-2424
WWW: http://www.kodak.com/
As mentioned above, Kodak has threatened legal action against developers who have tried to make details of the Photo CD format public, although the organization has not been completely successful in suppressing information. Source code has been posted to the Internet that will convert Photo CD files to PBM format (used by the pbmplus utilities described in Appendix C, Installation and Setup) and presumably remains available at many sites. As a consequence of this posting of information and source code, you may run across an application which reads and manipulates Photo CD format files, but which may not be properly licensed from Kodak. Always check to see if the application vendor is properly licensed.
Copyright © 1996, 1994 O'Reilly & Associates, Inc. All Rights Reserved.
