The KODAK Photo CD Master Disc

Five Image Resolutions Built In

The KODAK Photo CD Master disc is a multisession, write-once-read-many (WORM) type optical disc. The multisession capability allows the owner of a disc to add subsequent images to the disc after the original write session. Images can be opened and viewed on a computer using Photo CD enabled software.

The PIW's KODAK PCD Film Scanner 2000 uses a linear array CCD to create a 2048 by 3072 pixels scan (for 35 mm film that is about 2000 pixels per inch). The KODAK PCD Data Manager component of the PIW, working from the high resolution (2K by 3K pixels) scan, separates the luminance data from the chrominance data, and uses differing compression schemes to store the data efficiently. Photo CD uses the PHOTOYCC color encoding space, which is well suited to compression with minimal recognizable loss of detail. The image data components are stored together in an "Image Pac" format. Some or all of the Image Pac data is used when Photo CD "enabled" software rebuilds the image in whichever of the five different resolutions is requested.

Photo CD discs offer many advantages that make it practical for desktop computer users to work with images.

• Low-cost scans. People can have a 24-exposure roll of 35 mm film scanned onto a Photo CD Master disc for well under $25, much less expensive than previously available scanning services (or purchasing a desktop scanner).
• Multiple resolutions. The Kodak Image Pac file format on Photo CD discs stores each image at multiple levels of resolution. Users can work easily with the smaller, lower-resolution images on-screen, then use the highest resolution version for output.
• High-quality images. On a Photo CD Master disc, the highest resolution level (2048 x 3072 pixels) captures all the image data 35 mm film has to offer. Kodak has introduced Photo CD applications that offer higher resolutions for applications such as professional photography and color prepress operations.
• Convenient storage. Each Photo CD Master disc provides long-term, low-cost storage of about 100 images; other Photo CD applications can store more images at lower resolution.

The resolutions available from a KODAK Photo CD Master Disc are:

1. "Base*16" = 2048 x 3072 pixels = Photo quality, high resolution = 18 MB RGB digital file
2. "Base*4" = 1024 x 1536 pixels = HDTV quality = 4.5 MB RGB digital file
3. "Base" = 512 x 768 pixels = TV Image = 1.2 MB RGB digital file
4. "Base/4" = 256 x 384 pixels = large thumbnail = 300 kB RGB digital file
5. "Base/16" = 128 x 192 pixels = small thumbnail = 75 kB RGB digital file

Note: The files are stored on the Photo CD in PHOTOYCC color space, not RGB. Approximate file sizes are given for reconstructed RGB images as a reference point.

The Image Pac format enables extremely efficient storage, with an average Image Pac file size of 4.5 MB. The actual file size varies from picture to picture-- some scenes compress better than others. Image Pacs can range from 2.5 MB to 6 MB. Photo CD Master discs have a capacity to hold about 100 (perhaps more) images in Image Pac format.