digital_imaging by fanzhongqing

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									SEMINAR ON
     DIGITAL IMAGING




Prepared By :
              CONTENTS

Introduction
What is digital imaging
Technical aspect
 Digital Imaging of Office Records
Advantage
Disadvantage
Conclusion
     In 1996, Digital Imaging Technologies ("DIT")
was born, the Northeast's first completely digital
photography and digital design studio .

       Using the Web to make retrospective resources
accessible to a broad public raises issues of image
quality, utility, and delivery at the user's end. User
studies have concluded that researchers expect fast
retrieval, acceptable quality, and complete display of
digital images.
     What is digital imaging
     Digital imaging is referred as
scanning is process where by a paper
based document is       scanned by a
computer and converted from its
original human readable format in to a
digital computer readable format . T he
resulting image can be stored on a
variety of media such as computer disk
, CD-ROM , Magnetic tape and computer
servers . You can think of it as a
photocopy that can be viewed on your
computer .
           Technical aspect
PIXEL
       A digital image is usually a rectangular grid
comprised of individual pixels (picture element or PEL). A
good analogy might be a tile mosaic, with the smallest
element in the mosaic being the individual tiles (each of
which is one color or shade). Each pixel in a digital image
has a bit-depth value, which informs the computer which
color (or shade of gray) the pixel will display (the greater
the bit-depth value, the more colors/grays to choose
from). The combined effect of all the individually colored
pixels creates the image.
Resolution
The number of pixels in an image is often used as a way to describe the image's
resolution. The word resolution has a specific technical meaning to microscope users,
namely the ability to distinguish between two closely adjacent objects at a given
magnification. In the context of digital images, the word resolution usually refers to
how frequently an object was sampled.

The same object sampled at four different pixel densities
(Note: If you can stand back approximately 3 m from your computer screen, the
perceived difference between these images begins to decrease.)




     3X6              13 X 25         25X 50          100 X 200
Image resolution is often confused with the resolution of the
output device (computer monitor or printer). Output devices
typically express their resolution in dots/inch (DPI). Digital
imaging software programs (e.g., Adobe Photoshop™) often set
their scale factors based on the monitor resolution (72 DPI),
however, this setting is really only useful for images that will
ultimately be displayed on a monitor (WWW pages). Too often I
have seen people unnecessarily reduce the size of their images
based on the 72 DPI setting and in the process "throw away"
pixels (down-sampling), going from a crisp image like the right-
most image above, to the equivalent of the next image to the
left. With scientific/microscopic images this is an unacceptable
loss of data. Printers often refer to their maximum output
resolution in dots per inch (e.g., laser printers range from 300-
1200 DPI, inkjets 1440 DPI, dye-sublimation printers 300 DPI,
etc.
                        Bit-Depth
       The bit-depth of an image can greatly affect the size
of the computer file, in this example the image size is
assumed to be 1024 by 1024 pixels. Images with only two
colors are binary, the pixels are either black or white.
Monitors and imaging hardware are typically limited to
displaying grayscale images in 8-bit mode (256 shades of
gray). Most monitors can only display color images in a
maximum of 24-bit mode (true color), due to the
limitations of the electronics in the cathode ray tube. Even
these ranges are greater than the sensitivity of the human
eye, which is often stated as only being able to detect 16-
32 shades of gray and roughly 2,000,000 colors.
Color
      The most commonly used color model is
RGB (Red, Green, Blue) for on-screen color.
RGB is an additive color model, the three
different phosphors on the monitor screen are
excited at different intensities (usually an 8-bit
range for each color, for 256 intensities per
color, for a total of 16.7 million possible colour
combinations).
File Formats
There are a large number of available file formats for storing digital images. The majority of the
file formats are proprietary, and are specific to a given software program or specific uses (e.g.,
medical diagnostic imaging). Several well known file formats include:
       BMP - windows bitmap
       EPS - encapsulated postscript, this format is more useful for vector-based information than
       pixel-based information
       GIF - graphics exchange format, originally copyrighted by CompuServe, used on web pages,
       has a 256 color palette limitation, not suitable for most scientific images
       JPEG - joint photographic experts group, supports 24-bit color, uses a lossy compression
       technique (discrete cosine function), most often used on web pages, not suitable for most
       scientific images. The proposed JPEG-2000 format will use the lossless wavelet-based
       compression technique.
       PNG - portable network graphics, supports 48-bit color and 16 grayscale, lossless
       compression, a relatively new format that is not widely supported yet
       TIFF - tagged image file format, originally developed by Aldus Corp. (which was purchased
       by Adobe Systems) & Microsoft Corp., supports palette images (up to 8 bit), 8 & (in some
       programs) 16 bit grayscale as well as 24 bit color, this is probably the most commonly used
       file format for scientific images.
Digital Imaging of Office Records

     Your office may be considering
the benefit of imaging your paper
based office records . Digital
imaging can be a useful tool for
managing your records , but there
are many issues that should be
considered before committing to a
digital imaging project .
          Cost of digital imaging project
There are five factors which determine the project cost .
1.Document preparation
Cost of document preparation counts 1/3 rd of the cost of the project .cost of
document preparation depends upon the condition of records .
2.Digital imaging
The cost of digital imaging is effected by the size and quality of original
paper records ,the quality of print on the records and the technical
requirements of image.
3.Intangible cost
Staff time resources and hiring a vendor also cost to a project .
4.Long term cost
The long term cost also a key cost in imaging project . These cost include to
use CD-ROMS ,computer disk , magnetic tape and other data storage
devices .
Is digital imaging right for my records?
      Digital imaging is a process primarily
designed to improve access to records . Digital
imaging is most beneficial for frequently used
records in short time by multiple people . It can
also be a useful way of managing vary large
volume of records . Digital imaging is not usually a
recommended for records with a permanent
retention period , i.e it should not be used a s an
alternative to store large paper records, so a cost
benefit analysis should be made before a digital
imaging project to minimize the project cost .
                   Advantage
       The ability of the operator to post-process the image. Post-
processing of the image allows the operator to manipulate the pixel
shades to correct image density and contrast, as well as perform
other processing functions that could result in improved diagnosis
and fewer repeated examinations .

       With the advent of electronic record systems, images can be
stored in the computer memory and easily retrieved on the same
computer screen and can be saved indefinitely or be printed on
paper or film if necessary.
      All digital imaging systems can be networked into practice
management software programs facilitating integration of data.
With networks, the images can be viewed in more than one room
and can be used in conjunction with pictures obtained with an
optical camera to enhance the patients’ understanding of treatment
        Digital imaging allows the electronic
transmission of images to third-party providers, referring
dentists, consultants, and insurance carriers via a
modem.       Digital imaging is also environmentally
friendly since it does not require chemical processing. It
is well known that used film processing chemicals
contaminate the water supply system with harmful
metals such as the silver found in used fixer solution.

      Radiation dose reduction is also a benefit
derived from the use of digital systems. Some
manufacturers have claimed a 90% decrease in radiation
exposure, but the real savings depend on comparisons.
Disadvantage
There are also disadvantages associated with the use of digital
systems.
       The initial cost can be high depending on the system
used, the number of detectors purchased, etc. Competency
using the software can take time to master depending on the
level of computer literacy of team members.

         The detectors, as well as the phosphor plates, cannot
be sterilized or autoclaved and in some cases CCD/CMOS
detectors pose positioning limitations because of their size and
rigidity. This is not the case with phosphor plates; however, if a
patient has a small mouth, the plates cannot be bent because
they will become permanently damaged .
    Phosphor plates cost an average of $25 to
replace, and CCD/CMOS detectors can cost more
than $5,000 per unit. Finally, since digital imaging
in dentistry is not standardized, professionals are
unable to exchange information without going
through an intermediary process. Hopefully, this
will change within the next few years as
manufacturers of digital equipment become
DICOM compliant.
                  Conclusion

       Whether or not you switch to digital imaging, digital
is and will remain a force in the photo universe. If you are
interested in digital, rent or borrow a digital camera to get
the feel of it. Spend some time with a friend who shoots
digitally and see how they handle their digital workflow. In
time, I think that digital photography , scanning , printing
etc. will be the norm and that film will fall far behind.
Whether or not you agree, it only makes sense to
investigate digital as an alternative medium. Then you can
decide for yourself if it is time to switch.
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