Advanced Photography Course

necessary to direct the electron beam so it strikes the
correct phosphor dots as the electron gun scans the
screen (fig. 3-9).

Color monitors are available from standard EGA

levels to pixel levels of 2,048 by 2,048. The monitor
that is selected for your imaging system must match the
display card in the computer, since it is the display card
that limits the resolution of the monitor.

DIGITAL-IMAGE FILE STORAGE

Color digital images take up an extremely large

amount of memory when they are stored. Methods,
such as optical media, have been developed to
overcome this storage problem. Optical media is very
suitable for storing digital photographs. Some
examples of optical media include the following: Write
Once, Read Many (WORM) disks, erasable optical
disks, and optical memory cards. An example of
nonerasable memory is the Kodak Photo CD; this CD
allows high-quality color images to be stored for
archival and retrieval purposes.

One Kodak Photo CD can store up to 650

megabytes. This equates to 100 high-resolution, color
digital images when stored in compressed form. These
images are stored at five different resolution levels,

ranging from 128 by 192 pixels for a proof, or thumbnail

sketch, to a high resolution 2,084 by 3,072 pixels
(compressed) full-color image. These images can be
imported using photo software packages, then they can

Figure 3-9.--Cross section of a CRT.

be manipulated, printed, or placed in various layout
applications.

Image compression makes it possible to take a large

color-image file and reduce its size. This reduces the
amount of memory required to store it or decreases the
time required to transmit it. Compression can reduce
the amount of memory needed by a factor from five to
one hundred. Various compression-decompression
chips, add-on boards, and software are available in the
commercial market.

Image compression is made possible because in a

typical digitized image, the same information appears
several times. For example, areas of the same color in
different parts of the image or straight lines contain the
same information. This duplication of information
values, or REDUNDANCY, can be identified in three
types as follows:

Spatial redundancy. This results from

dependence among neighboring pixel values.

Spectral redundancy. This results from an

association of color (RGB) planes.

Temporal redundancy. This results from a
correlation between different frames in a

sequence of images.

The most common compression program has been

formed by the Joint Photographic Experts Group
(JPEG). The technique used in JPEG compression
allows the user to select the compression ratio.

High-compression ratios generally result in low

image quality. This low image quality is a result of

avoiding the risk of losing data as the image

compression ratio is increased. The amount of image
compression depends on the amount of redundancy that
exists in an image. When a compressed image is
reconstructed (uncompressed) and the pixel values are
identical to the original image, the compression is
known as lossless. When discrepancies occur between
the original and the reconstructed image, the
compression is called lossy. Lossless compressions can
be achieved with compression ratios of up to 5 to 1.
Files that are compressed may be identified by the file
extension ".JPG."

HARDCOPY OUTPUT

A number of methods for making digital

photographs are used. Some of these technologies
include the thermal-dye transfer, inkjet, thermal-wax

3-13

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Advanced Photography Course

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DOFMaster for Windows On-line Depth of Field Calculator DOFMaster for Mobile Devices On-line Depth of Field Table Hyperfocal Distance Chart Articles FAQ Recommended Books Support Contact Links Home As an Amazon Associate I earn from qualifying purchases.	contents <- previous page next page -> necessary to direct the electron beam so it strikes the correct phosphor dots as the electron gun scans the screen (fig. 3-9). Color monitors are available from standard EGA levels to pixel levels of 2,048 by 2,048. The monitor that is selected for your imaging system must match the display card in the computer, since it is the display card that limits the resolution of the monitor. DIGITAL-IMAGE FILE STORAGE Color digital images take up an extremely large amount of memory when they are stored. Methods, such as optical media, have been developed to overcome this storage problem. Optical media is very suitable for storing digital photographs. Some examples of optical media include the following: Write Once, Read Many (WORM) disks, erasable optical disks, and optical memory cards. An example of nonerasable memory is the Kodak Photo CD; this CD allows high-quality color images to be stored for archival and retrieval purposes. One Kodak Photo CD can store up to 650 megabytes. This equates to 100 high-resolution, color digital images when stored in compressed form. These images are stored at five different resolution levels, ranging from 128 by 192 pixels for a proof, or thumbnail sketch, to a high resolution 2,084 by 3,072 pixels (compressed) full-color image. These images can be imported using photo software packages, then they can Figure 3-9.--Cross section of a CRT. be manipulated, printed, or placed in various layout applications. Image compression makes it possible to take a large color-image file and reduce its size. This reduces the amount of memory required to store it or decreases the time required to transmit it. Compression can reduce the amount of memory needed by a factor from five to one hundred. Various compression-decompression chips, add-on boards, and software are available in the commercial market. Image compression is made possible because in a typical digitized image, the same information appears several times. For example, areas of the same color in different parts of the image or straight lines contain the same information. This duplication of information values, or REDUNDANCY, can be identified in three types as follows: Spatial redundancy. This results from dependence among neighboring pixel values. Spectral redundancy. This results from an association of color (RGB) planes. Temporal redundancy. This results from a correlation between different frames in a sequence of images. The most common compression program has been formed by the Joint Photographic Experts Group (JPEG). The technique used in JPEG compression allows the user to select the compression ratio. High-compression ratios generally result in low image quality. This low image quality is a result of avoiding the risk of losing data as the image compression ratio is increased. The amount of image compression depends on the amount of redundancy that exists in an image. When a compressed image is reconstructed (uncompressed) and the pixel values are identical to the original image, the compression is known as lossless. When discrepancies occur between the original and the reconstructed image, the compression is called lossy. Lossless compressions can be achieved with compression ratios of up to 5 to 1. Files that are compressed may be identified by the file extension ".JPG." HARDCOPY OUTPUT A number of methods for making digital photographs are used. Some of these technologies include the thermal-dye transfer, inkjet, thermal-wax 3-13 contents Advanced Photography Course <- previous page next page ->	As an Amazon Associate I earn from qualifying purchases.
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