DISPLAYS AND IMAGE PROCESSING
Bistable vs Gray Scale Display
Bistable composed by 2 shades - Black and White (high contrast, narrow range)
Gray Scale present multiple levels of brightness white, light gray, medium gray, dark gray.. based on different echos
amplitudes and different biologic tissue (low contrast, wide range)
Display Controls
Contrast - Determines the range of brilliance within the display image. Only white and Black and high with ⇡
contrast.
Brightness - Determines the of brilliance within the display image
Scan Converts - First store the information and than display it. Store information is called writing and later
displaying it is called read. It changes the format of data by translating the information from the spoke format into
the video format. The modern digital scan converters use computer technology.
Analog vs. Digital Numbers
Analog numbers are real worlds found in hour everyday lives. Unlimited and continuous range of values.
Digital numbers associated with computer devices having only discrete values.
Analog Scan Converter - Funnel shaped vacuum tube with an electron gun located within the smaller end. Charger
with electrons particles containing the image information. The largest end of the tube contain a dielectric matrix or
silicon wafer. The electrons strike the matrix where they are stored.
Note: spatial resolution is image detail.
Note: Analog ⇢ Digital ⇢ Analog {Analog to digital is processing/post-processing}{Dig. to Analog is display}
Limitations - Image fade, flickers, instability, deterioration
Digital Scan Converter - Convert images into numbers by digitizing. Stores in a computer memory as a series of
zeros and ones. composed by 2 elements: Pixel and Bit
Advantages - Uniformity, stability, durability, speed, accuracy.
Pixel - Smallest building block of a digital picture composed by shades of gray (more shades, more details)
Pixel Density - Number of picture elements per inch.
Low pixel density - Few pixels per inch, large pixels (box), less detail, lower spatial resolution
High pixel density - Many pixels per inch, smaller pixels (box), more detail, high spatial resolution
Bit - Smallest amount of computer memory. Bistable having value of either 0 or 1
Binary number - group of bits composed by zeros and ones (digital)
Byte - group of 8 bits
Word - 2 bytes or 16 bits
Note: Images with many gray shades have better contrast resolution.
# of bites Exponents Number of shades
1 2^1 2
2 2^2 4 (2x2)
3 2^3 8 (2x2x2)
4 2^4 16 (2x2x2x2)
5 2^5 32
8 2^8 256
Fewer Bits More Bits
few shades More shades
degraded contrast. Improves contrast
How many possible shades of gray are displayed
with 5 bits of memory ?
2^5 = 2x2x2x2x2 = 32 different gray shades
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