C2A: Memory and Display

Question 1

historically, was scan conversion an analog or digital process? what about today

Answer 1

analog

now use digital

Question 2

describe the differences b/w analog and digital scan conversion

Answer 2

analog:
- shows you continuous values
- prone to drift
- less reproducible
- no long term memory

digital:
- shows discrete numbers
- stable
- reproducible
- good long term memory

Question 3

can you cine w/ an analog scan converter

Answer 3

no, theres no long term memory

Question 4

what are the main advantages of the analog scan converter

Answer 4

• allowed for grey scale
• act as a buffer b/w image and display
• good short term memory

Question 5

whats a typical dimension of a matrix for a digital scan converter (DSC) ? is it divided into smaller squares

Answer 5

1024x768

…yes, divided into pixels which each contain a digital number

Question 6

what does the digital number assigned to each pixel represent

Answer 6

the amplitude of the received echo (will be equal to a 1 or a 0)

Question 7

what does each pixel store?

Answer 7

stores data that represents the greyscale information of the returning echos

Question 8

what type of ‘language’ does a DSC use?

Answer 8

binary code

Question 9

how many shades of grey can each pixel in the matrix display?

Answer 9

2

Question 10

how do we get additional shades of grey if each pixel in a matrix can only produce 2/

Answer 10

-additional matrices are stacked on top of one another so that each pixel location can be represented by many 1s or 0s

Question 11

whats the smallest form of display w/ a DSC

Answer 11

pixel

Question 12

what is a bit

Answer 12

1 binary digit

Question 13

what is a byte

Answer 13

8 bits of data (e.g. 10010101)

Question 14

whats a word

Answer 14

combination of bits expressed as a unit (e.g. 10010101)

Question 15

what is word length

Answer 15

the # of bits in a word (e.g. 1001010 has 7 bits so a word length of 7)

Question 16

what is bit depth

Answer 16

the word length at each address location (US has a bit depth of 8)

Question 17

describe RAM

Answer 17

random access memory

• fast, rewritable, cheap and erased when the machine is turned off
• the machines ‘operating system’

Question 18

describe ROM

Answer 18

read only memory (you cant change it)

• permanent and used for system functions
• machines ‘program software’

Question 19

how do you find the # of shades of grey you can produce

Answer 19

2^n

n= # of bits of the bit depth used at each address location

Question 20

as you increase bit depth what happens to the # of shades of grey you can produce

Answer 20

it increases

Question 21

review how to convert binary # to decimal

Answer 21

/

Question 22

the US systems resolution is limited by what?

Answer 22

the monitor resolution… US machine is limited by the type/quality of display used

Question 23

what are the 2 considerations for monitor quality

Answer 23

• # of pixels

- size of pixels

Question 24

why are more pixels better

Answer 24

because in order to fit into a finite space, the pixels need to get smaller so theres better resolution

Question 25

do we impact the resolution by changing the field of view

Answer 25

yes

Question 26

how do you calculate resolution

Answer 26

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

Question 27

what was the first type of CRT

Answer 27

oscilloscope

Question 28

describe the oscilloscope CRT

Answer 28

could only display in X, Y axis and was not able to produce a video signal (image)

Question 29

which early methods of US used an oscilloscope for display

what do we use today

Answer 29

A mode and B mode and M mode

LCD monitor

Question 30

what type of CRT accept a video signal and can display a wide range of shades of grey

Answer 30

TV CRT

Question 31

describe the CRT

Answer 31

• 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

Question 32

what does the # of electrons hitting the phosphorus plate depend on

Answer 32

amplitude of the video signal

Question 33

how do you produce colour w/ a CRT

Answer 33

need 3 electron guns that cause the phosphorus to light up as red, green or blue (which produce all necessary colours)

Question 34

how is the E beam moved across the phosphorus plate w/ a CRT

Answer 34

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

Question 35

a complete image frame w/ raster and interlacing has how many lines? what is its frame rate

Answer 35

525 lines every 1/30 seconds

so 30 FPS or Hz for a whole frame

Question 36

whats the time is takes to produce a single field w/ a CRT

Answer 36

1/60 a second for EACH frame (odd and then even)

Question 37

why do we use interlacing

Answer 37

to reduce flicker

Question 38

why are computer monitors superior to CRT

Answer 38

• they have more scan lines
• smaller and more pixels
• better resolution (1024x768 or more)
• higher frame rates

Question 39

how are scan lines written on a computer monitor

Answer 39

progressively… still w/ raster format (top to bottom, L to R)

Question 40

FPS is higher than what value w/ computer monitors

Answer 40

> 60 Hz