Photo CD FAQ

What is Photo CD?

Photo CD is a system introduced by Kodak for digitizing and storing black and white or color negatives or transparencies on compact disks your computer can read. Each disk can hold about 100 high quality images.

You can have a Photo CD made from your film at the same time it is developed, or you can have a disk made from a collection of slides or cut negatives. The first method is more convenient and costs less per frame; the second method lets you choose the images you want scanned and usually costs less overall. You can also have images appended to an existing Photo CD; this creates what is called a multisession disk.

Regardless of whether you start with a negative or a slide, your photographs are stored on the CD as positive images, and you can get excellent results from either. Kodak does not currently offer a service for scanning prints to Photo CD -- to do this you will either need a flatbed scanner or you will need to photograph the prints and send in the film to be developed and scanned.

What kinds of Photo CDs are there?

Standard Master disks contain all image resolutions up to 2048x3072. Catalog disks only go up to 512x768 (but can store many more images per disk). The new Professional disks can optionally include 4096x6144 pixel (base*64) images and can be made from 35mm, medium format, or even 4x5 sheet film. These Professional Photo CD scans are however much more expensive than the normal 35mm Master Photo CD scans, and each Professional Photo CDs holds only 25 images if you include the base*64 resolution. Kodak also offers specialized versions of Photo CD for medical, prepress, and other uses.

We generally recommend using the base*4 image for making 8x10 prints. The much smaller base images are fine for making slide shows or 4x5 prints. The base*16 and base*64 images are more difficult to work with because of their size, and the improvement in image quality at a print size of 8x10 is relatively small.

Where can I get a Photo CD made?

Photo CD services are available through Digital Light & Color, certain mail order photo labs, Kodalux, and various local retail outlets and service bureaus. You can obtain a list of Photo CD service providers in your area from the Kodak Web Site .

How are images stored on the disk?

First, each image is scanned using a very high quality scanner that is part of the Kodak Photo CD workstation. The image is then encoded and stored on the CD in a range of different sizes using a special multiresolution format created by Kodak. The following table summarizes the avaialable Photo CD image resolutions in pixels, their names, and the corresponding file sizes in megabytes:

    Name     Resolution     File Size
    base/16  128x192        0.07MB
    base/4   256x384        0.29MB
    base     512x768        1.2MB
    base*4   1024x1536      4.7MB
    base*16  2048x3072      18.9MB
    base*64  4096x6144      75.5MB (Pro Photo CD only)

The images up to the base resolution (512x768) are stored uncompressed on the disk. The higher resolution images are stored as residuals -- each pixel is stored as the difference between it and the nearest pixel in the next lower resolution. These differences are typically small values which are then compressed using a technique call Huffman coding. Thus the space required to store the apparently redundant resolutions is kept to a minimum.

All the images are stored using a special color space called Photo YCC which can be resconstructed as 24-bit RGB. Photo YCC is simply a format in which they store a black and white image (the Y component also called the luminance component) and two color components (the C and C components also called the chrominance components) that specify the color of each pixel independent of its brightness. This format is nearly identical to the way a television signal is encoded, making the original Photo CD player that plugged directly into a TV set easy to design. Another way Kodak saves space on the CD is to store the color (chrominance) information at a lower resolution than the black and white information since the eye is more tolerant of errors in color than error in brightness.

How good is Photo CD image Quality?

The amount of information extracted from a photograph and stored on a Photo CD is truly amazing.

The image on the left shows a full frame Photo CD scan from a 35mm slide. The image on the right is an expanded view of the marked rectangle magnified by a factor of 8 revealing the wealth of fine detail captured by the Photo CD scanning process.

How permanent is a Photo CD?

Kodak has taken special precautions to ensure that Photo CDs will not deteriorate. To quote from a Kodak white paper on the topic of Photo CD permanence: "It is reasonable to expect a life of 30 years or more when discs are stored in normal home or office conditions." More recent statements by Kodak claim an expected lifetime of 100 years. Of course, you may have some difficulty finding a CD-ROM drive 100 years from now.

Can my CD-ROM drive read Photo CDs?

While virtually all CD-ROM drives manufactured in the last 4 years can read Photo CDs, many older drives will not. If you have an older drive or are considering purchasing a drive, confirm with your dealer or manufacturer that it is multisession Photo CD compatible.