What is PCD?
Image Format DescriptionPCD is the filename extension of Photo CD, Kodak's proprietary file format for storing images on photo CDs. Designed and launched by Kodak in 1992, the main objective of the PCD file is to digitalize, using a special compression encoding scheme, at least 100 images for storage and retrieval.
All conventional photographs, slides, and transparencies can be converted to Photo CD. The images are scanned and converted to PCD using PIW (PCD Imaging Workstation – consisting of a scanner, data manager, monitor, CD writer, printer, CD-ROM drive, and system software). The Photo CD has a particular directory structure that contains the images. These images are stored at five different resolutions – 1) Base/16 for thumbnail image (128 x 192 pixels); 2) Base/4 for rotated image on TV (256 x 384 pixels); 3) Base for TV and computer monitor display (512 x 768 pixels); 4) 4 Base for High Definition TV display (1,024 x 1,536 pixels); and 5) 16 Base for high resolution for 35 mm film (2,048 x 3,072 pixels). A sixth resolution of 64 Base for Pro Photo CD disk (4,096 x 6,144 pixels) can also be added.
In the PCD compression scheme, image files can be reduced to up to a third of the original file size without any visual loss of quality. During compression, some of the chrominance data is removed, but since the human eye is not very sensitive to color differences, the change is not visible -hence the words “without any visual loss”.
The Photo CD format is not very popular mainly because it is proprietary. Scanners are also easily and cheaply available, so the need for the format is not really felt. The main clients of Photo CD are photographers and graphics professionals due to its high end resolutions.
A Photo CD file can be read by any application that supports PCD – like a CD-i player, a Photo CD player, and any computer system with suitable software. The images can also be printed out using a special Kodak machine on photographic paper.
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