# 5200- Corel® PHOTO CD - General Information

The Corel® Professional PHOTO CD is an ISO 9660 CD-ROM disk that can be read by either
MacIntosh® or IBM machines. The PCD images are transferred from a Kodak (XA) formatted
disk to the ISO disk in order to be compatible with the widest variety of CD-ROM drives. As a
result, the Corel disks can NOT be read in a Kodak PHOTO CD-ROM player attached to a
television and do not require an XA compatible drive on a computer.

The Kodak PHOTO CD Process (In Brief)
Kodak images are digitized from 35mm slides or negatives at a resolution of 2048 x 3072 pixels
generating an 18 MB RGB file. The 18 MB file is then compressed by reducing the image data to
Luminance and Chrominance information which produces a smaller, 4.5 MB file called an Image
Pac. This file includes the image in 5 sizes: Thumbnail or Base/16, Base/4, Base (which is close to
the NTSC Television standard and similar to the MAC and VGA - 640 x 480), 4Base and 16Base
(see Table below).

In the process of scanning the image, the PCD Data Manager workstation automatically adjusts
the color of each image according to the make and type of film it is scanning. It will properly
balance more than 200 types of film. When importing bitmaps, some DTP (Desk Top Publishing)
applications will ask what type of film the original image was taken with in order to do some color
balancing. Since the Kodak process already performs this balancing when producing the original
image, no further balancing is required.

Printing and Converting PHOTO CD Images
PostScript Printers
There is no application supplied with the Corel PHOTO CDs that will allow one to print the
photo CD images. They must be converted to another file format and then imported into a
Drawing or Desk Top Publishing package. 

All printing will be handled by the application but the image quality will be dependent on the
resolution of the converted image, the physical size of the image and the resolution and screen
frequency of the printing device. How each of these parameters affects the final output is beyond
the scope of this document.

Non-PostScript Printers
If the images are being printed to a non-PostScript printer, the print quality will be primarily
dependent on the graphics card and driver that are being used to run Windows. A non-PostScript
printer driver creates the image that will be used for printing, directly from the video RAM so, if
the video is low resolution, low color, the printer will output a similar quality. PostScript printing
will generally give better results.

Converting/Exporting PHOTO CDs
When the conversion from PCD into a another file format (TIFF for instance) is performed, the
image that is produced has an effective scan rate of 300 DPI. Therefore, if the printer is set up for
a 150 LPI screen frequency, no modifications need to be done to the TIF image to produce the
best quality image without excessive file overhead.

Some points to remember before Converting/Exporting Images
The conversion process can take considerable time to complete if the larger file size is selected.
Even on a fast machine, the 2048 x 3072 may take as much as 30 minute before it finishes writing
the file to the hard disk. This file will be the largest and will be approximately 18 MB. As a result,
it will require a considerable amount of hard disk space and RAM to complete the conversion
successfully. If there is less that 12 MB of RAM on the system performing this export, it may not
be able to complete the conversion to the two larger sizes.

Image Resolution
When converting/exporting an image, regardless of the size the image, it will more than likely read
as a 72DPI ( dots per inch)  image in an application such as Adobe® Photoshop®.  The reason
for this is quite simple.  The images are stored in high resolution on the CD-ROM, but the
PHOTO CD format does not store the DPI value.  When these files are opened they will display
the default resolution (either 72 or 96 dpi).  To rectify this problem, simply re-sample the image,
with maintain file size checked, to the appropriate resolution and the images will become the new
size, without any loss of quality.

Glossary of Terms
DPI - Dots per Inch - a measure of the output resolution produced by printers, image setters or
monitors.

Lino - Linotype - This is a popular brand of image setter. It is very high resolution; generally at
least 1200 DPI.

LPI - Lines Per Inch - A measure of the frequency of a halftone screen (Usually ranging from
55-200). This terminology is a holdover from traditional printing methods of producing various
shades of the same color.

PCD - PHOTO CD Data format

PPI - Pixels Per Inch - A measure of the resolution of an electronic image from a source such as a 
scanner or a digital camera.

RIP - Raster Image Processor - Part of an output device that rasterizes information so that it may
be imaged onto film or paper. The RIP is one part of an imagesetter.

Screen Angle - The angles used to offset the different films in process color separations. If
correct screen angles are not used when printing, the final result will show Moir  or Rosette
patterns. This is a printing adjustment. It is not determined by the original image.

Screen Frequency - The number of lines per inch of a half tone screen. This is also a printing
setting