Displays - Ch 15 Flashcards
what are 5 characteristics of bistable display?
- 2 choices only - black or white
- on or off
- high contrast *
- narrow dynamic range *
- poor contrast resolution
what are 5 characteristics of gray scale display?
- many shades of gray
- multiples levels
- low contrast
- wide dynamic range
- good contrast resolution
what does the brightness control do?
related to the brilliance of the image
what does the contrast control do? what kind of images are high contrast?
determines the range of brilliances that are displayed. Are the whites white and blacks black? bistable images
what is analog display? examples?
Real world: a variable attains a continuum of values.
ex: actual weight of an individual or true length of a piece of string
what is digital display? example?
computer world: a variable attains only discrete values.
ex: measuring weight on a digital scale
what do scan converters do? why are these important?
changes the data format from penetrations (spokes) to horizontal lines of a display. made gray scale displays possible.
how can an image be manipulated using a scan converter? example?
can be manipulated in bw the “storing” and “displaying” of the data.
Ex: black on white image can be inverted into a white on black image
what is a digital scan converter?
a microprocessor that digitizes images. this converts the image into a string of zeroes and ones which are stored in memory. the numbers (digital image data) can be processed and then re-converted for display as an image.
what is a pixel?
the smallest element of a digital picture. If we divide pic into a grid each square is a pixel.
what is pixel density? what does it to?
pixels per inch; the more pixels per inch the more detail in the image, spatial or detail resolution.
what is spatial resolution on a digital display determined by?
the pixel density
what does spatial resolution pertain to?
related to the number of lines per frame
what is a bit? how would you describe it?
Binary digit - the smallest amount of digital storage; Bistable = having a value of either zero or one.
how are bits used? what does this mean?
a group of bits are assigned to each pixel to store the gray scale color assigned to that pixel. the more bits per pixel, the more shades of gray = better contrast resolution.
what is a binary number? how do you know it’s considered binary?
a group of bits, a series of zeroes and ones; digital (computer-based) means binary.
what is a byte? a word?
a group of 8 bits = byte; 2 bytes (16 bits) is a word
binary numbers are based on _____. decimal numbers are based on _______.
2; 10
digital means __________ not _______.
binary; decimal
what is the formula for determining the number of gray shades displayed?
2^n, n being number of bits
how many bits are needed to represent 10 shades of gray?
4 bits; bc 4 bits = 16 shades and 3 bits = 8. therefore, at least 4 bits are needed to display 10 shades of gray.
in image processing, what is preprocessing? what is important about this?
manipulating the data before storage in the scan converter. once preprocessing occurs, the data is altered forever and cannot be reversed.
what 6 things occur during preprocessing?
- TGC
- dynamic range
- write magnification
- fill-in interpolation
- persistence (frame averaging)
- spatial compounding
what is dynamic range/ log compression? what does it do? can this be controlled by the sonographer?
related to ability of humans to see the gray scale difference in anatomic structures; log compression lowers the high echoes and boosts the low lvl echoes. the image data’s dynamic range is reduced. controlled by sonographer.
what is postprocessing? what does it do? what is it performed on?
manipulating the data after it has been stored in the scan converter memory but prior to display; Increases versatility of the display process and can be undone; postprocessing is performed on frozen images.
what two things are done during postprocessing?
read magnification and 3-D rendering
processing is pre or post based on what?
on whether data is stored in the scan converter. if we have the info in image form, then it is post processing
analog= ______ _________ digital =___________
real world; computers/digital
how does analog to digital conversion work? what is used to do this?
electrical signals created by the PZT are analog, but a digital scan converter can only process computer info. Therefore, analog signal must be converted into digital form for input into the scan converter; digital-to-analog converter
