C2A: Memory and Display Flashcards
historically, was scan conversion an analog or digital process? what about today
analog
now use digital
describe the differences b/w analog and digital scan conversion
analog:
- shows you continuous values
- prone to drift
- less reproducible
- no long term memory
digital:
- shows discrete numbers
- stable
- reproducible
- good long term memory
can you cine w/ an analog scan converter
no, theres no long term memory
what are the main advantages of the analog scan converter
- allowed for grey scale
- act as a buffer b/w image and display
- good short term memory
whats a typical dimension of a matrix for a digital scan converter (DSC) ? is it divided into smaller squares
1024x768
…yes, divided into pixels which each contain a digital number
what does the digital number assigned to each pixel represent
the amplitude of the received echo (will be equal to a 1 or a 0)
what does each pixel store?
stores data that represents the greyscale information of the returning echos
what type of ‘language’ does a DSC use?
binary code
how many shades of grey can each pixel in the matrix display?
2
how do we get additional shades of grey if each pixel in a matrix can only produce 2/
-additional matrices are stacked on top of one another so that each pixel location can be represented by many 1s or 0s
whats the smallest form of display w/ a DSC
pixel
what is a bit
1 binary digit
what is a byte
8 bits of data (e.g. 10010101)
whats a word
combination of bits expressed as a unit (e.g. 10010101)
what is word length
the # of bits in a word (e.g. 1001010 has 7 bits so a word length of 7)
what is bit depth
the word length at each address location (US has a bit depth of 8)
describe RAM
random access memory
- fast, rewritable, cheap and erased when the machine is turned off
- the machines ‘operating system’
describe ROM
read only memory (you cant change it)
- permanent and used for system functions
- machines ‘program software’
how do you find the # of shades of grey you can produce
2^n
n= # of bits of the bit depth used at each address location
as you increase bit depth what happens to the # of shades of grey you can produce
it increases
review how to convert binary # to decimal
/
the US systems resolution is limited by what?
the monitor resolution… US machine is limited by the type/quality of display used
what are the 2 considerations for monitor quality
- # of pixels
- size of pixels
why are more pixels better
because in order to fit into a finite space, the pixels need to get smaller so theres better resolution
do we impact the resolution by changing the field of view
yes
how do you calculate resolution
take the depth in mm and divided it by the # of pixels horizontally across the screen…. you want max number of pixels w/ least amount of depth possible
e.g. 1024x1024 and 20 cm -> 200mm/1024 = 0.2 mm/pixel
what was the first type of CRT
oscilloscope
describe the oscilloscope CRT
could only display in X, Y axis and was not able to produce a video signal (image)
which early methods of US used an oscilloscope for display
what do we use today
A mode and B mode and M mode
LCD monitor
what type of CRT accept a video signal and can display a wide range of shades of grey
TV CRT
describe the CRT
- has a tube that contains a cathode or source of electrons (-)
- the electron beam is directed towards the phosphor plate which is +
- electrical or magnetic deflection plates are used to steer the beam of electrons onto the plate
- brightness of phosphorus depends on # of electrons hitting the plate
what does the # of electrons hitting the phosphorus plate depend on
amplitude of the video signal
how do you produce colour w/ a CRT
need 3 electron guns that cause the phosphorus to light up as red, green or blue (which produce all necessary colours)
how is the E beam moved across the phosphorus plate w/ a CRT
Raste Format w/ interlacing
Raster is from top to bottom, L to R
Interlacing is writing all of the odd lines and then all the even lines on the screen
a complete image frame w/ raster and interlacing has how many lines? what is its frame rate
525 lines every 1/30 seconds
so 30 FPS or Hz for a whole frame
whats the time is takes to produce a single field w/ a CRT
1/60 a second for EACH frame (odd and then even)
why do we use interlacing
to reduce flicker
why are computer monitors superior to CRT
- they have more scan lines
- smaller and more pixels
- better resolution (1024x768 or more)
- higher frame rates
how are scan lines written on a computer monitor
progressively… still w/ raster format (top to bottom, L to R)
FPS is higher than what value w/ computer monitors
> 60 Hz
