UNIT 3: Digital Display Characteristics & QC

Question 1

Steps in Digital to Analog conversion

Answer 1

1. Coding
2. Quantization
3. Sampling
4. Scanning

Question 2

Do we need to see the image in Digital or Analog form?

Answer 2

Analog form

Question 3

Two processes in which image data is formatted to fit a display monitor

Answer 3

Decimation and Interpolation

Question 4

Formatting for display: Decimation

Answer 4

Image data is larger than monitor matrix size
-Information is sampled
-Some detail is lost

Question 5

Formatting for display: Interpolation

Answer 5

Image data is smaller than the monitor matrix size
-Information is combined and averaged to fill in empty pixels
-Image may become blurry

Question 6

Primary vs secondary display

Answer 6

Primary: Radiologists monitor
Secondary: Radiographers work station

Question 7

Soft copy viewing LCD monitors: LCD with Cathode Backlight

Answer 7

• Monitor sizes are limited
• Lower initial cost
• Shorter lifespan
• More popular

Question 8

Soft copy viewing LCD monitors: LCD with Light Emitting Diode(LED)

Answer 8

• Monitors can be customized
• Longer Lifespan
• Higher initial cost
• Superior image quality

Question 9

Layers in the LCD monitor

Answer 9

-Backlight
-Polarized filters
-TFT layer
-Liquid Crystal layer

Question 10

Backlight

Answer 10

Providing light for monitor

Question 11

Polarized filters

Answer 11

Hold liquid crystal material in place

Question 12

TFT layer

Answer 12

Send/Apply electricity current to liquid crystal layer

Question 13

Liquid Crystal layer

Answer 13

Material used to create image on monitor, allows varying amounts of light to pass through it

Question 14

Monitor characteristics: Resolution

Answer 14

Controlled by matrix size

Question 15

Monitor characteristics: Luminance

Answer 15

Brightness produced at the monitor

Question 16

Monitor characteristics: Contrast

Answer 16

The differences between adjacent areas of IR exposure on the image

Question 17

Monitor characteristics: Bit Depth

Answer 17

Quantity of shades of gray the monitor displays

Question 18

Monitor characteristics: Uniformity

Answer 18

Even exposure throughout the image in the absence of any attenuating materials

Question 19

Monitor characteristics: Glare

Answer 19

Occurs when too much ambient light scatters around an object making the image appear “washed out”

Question 20

How is viewing the digital image affected by the inverse square law?

Answer 20

Luminance decreases as you increase distance from the monitor

Question 21

How is viewing the digital image affected by the Cosine law?

Answer 21

when the monitor is viewed from an angle both the contrast and luminance is reduced

Question 22

Cosine law

Answer 22

Angular dependence. The best viewing angle of a digital display device is straight on.

Question 23

Grayscale Standard Display Function (GSDF)

Answer 23

a DICOM standard to provide a consistent appearance of grayscale between displays

Question 24

Perceptual Linearization

Answer 24

equal changes in digital values result in equal changes in perceived brightness values

Question 25

QC test patterns used in display monitor performance tests

Answer 25

-SMPTE -TG-18 (AAMP)

Question 26

What is a photometer used for?

Answer 26

-Luminance meter -Test for brightness emitted from the monitor

Question 27

Monitor and Display system QC

Answer 27

Brightness Contrast Resolution Distortion Reflection Angular Dependence

Question 28

Monitor quality

Answer 28

•Resolution •Luminance •Contrast •Bit Depth •Uniformity •Glare

Question 29

SMPTE Image

Answer 29

Question 30

TG-18 (AAPM) Image

Answer 30

Question 31

Hard copy images

Answer 31

-Refers to images in a form that can be touched -Examples: Paper, Film

Question 32

Hard copy devices and storage media

Answer 32

-Paper (thermal) printers or film (laser) printers -Hard storage disks, such as DVD or CD’s, or SSD such as Flash media

Question 33

Soft copy images

Answer 33

Images that can only be seen. Terms that refer to soft copy devices include: a. Monitors b. LCD or CRT c. Display d. Medical display

Question 34

Before the latent digital image can be viewed on a monitor it must undergo

Answer 34

Digital to Analog Conversion

Question 35

Information to Image transformations

Answer 35

The algorithms used to take input digital data and produce output in a form of an analog image

Question 36

T or F: all soft copy displays emit a light signal in an analog form for humans to be able to see the image

Answer 36

True

Question 37

Lumen

Answer 37

The basic unit of light intensity

Question 38

Luminance

Answer 38

a measurement of the amount of lumen or brightness emitted onto an entire viewing area, such as a digital display

Question 39

Advantages and Disadvantages of LCD monitor

Answer 39

Advantages of LCDs: • Lower energy consumption • Lighter and thinner • Less heat produced (especially LED backlit models) Disadvantages of LCDs • Angular dependence: loss of contrast at larger viewing angles • Images not as bright and color reproduction not as good as CRTs

Question 40

Advantages and Disadvantages of CRT monitor

Answer 40

Advantages of CRTs: • Very bright images even at greater viewing angles • Very fast refresh rate (# of times the screen refreshes per second) – produces less blur in dynamic imaging Disadvantages of CRTs • High energy consumption • Higher heat production • Large (deep) and heavy

Question 41

Matrix

Answer 41

an array of pixels arranged in columns and rows

Question 42

Decimation or sub-sampling is used when the input matrix size to too _______ for the output device matrix

Answer 42

large

Question 43

Interpolation is used when the input image matrix is too _______ for the output device matrix.

Answer 43

Small

Question 44

What are the two types of luminance meters?

Answer 44

• Near-range – used in close proximity to the surface of the display • Telescopic – used to test from a distance of 1m

Question 45

Types of Test Typically Performed:

Answer 45

• Geometric Distortion • Reflection • Luminance response • Luminance non-uniformity • Display Resolution • Display Noise

Question 46

Geometric Distortion

Answer 46

size and shape of the displayed image is different from the original (acquired) image

Question 47

Reflection

Answer 47

ambient light interfering with the internal display light. Can be specular – mirror images (reflections) of other light sources or objects in the room; or diffuse, randomly scattered light onto the display surface

Question 48

Display Resolution

Answer 48

Measure of the ability of the digital display to produce separate images of two points with high fidelity. Test performed using a test pattern.

Question 49

Display Noise

Answer 49

High frequency patterns or fluctuations that interfere with the true signal. Test is performed using a test pattern.

Question 50

Response rate

Answer 50

The amount of time it takes for the crystal to go from an on to an off state and vice versa.

Question 51

Aspect ratio

Answer 51

the ratio of the width to the height of the monitor – most LDC’s are 16:9 (widescreen)

Question 52

Aperture Ratio

Answer 52

the portion of the pixel face that is available to transmit light

Question 53

Viewable area

Answer 53

measurement diagonally from one corner to the opposite of the viewing screen (does not include the casing).