Photometry & Human Vision
Photometry is the study of what?
Human visual response to visible light
Which unit expresses luminance of a digital display?
Candela per square meter
Liquid crystals are useful in displays because they:
Align when an electric field is applied
What is a key advantage of soft-copy interpretation over hard-copy images?
Soft copy allows image manipulation
Digital subtraction angiography improves visualization by doing what?
Removing background anatomy
The CIE is important because it standardized what?
Human visual response to light
Illuminance measures what?
Light incident on a surface
In an LCD pixel, brightness is controlled by what?
Liquid crystal orientation
Preprocessing refers to manipulation that occurs when?
Automatically before image display
Pixel shift is used to correct what issue?
Patient motion between images
Photopic vision primarily uses which photoreceptors?
Cones under bright lighting
According to the cosine law, brightness does what as viewing angle increases?
Decreases
Increasing megapixel count primarily improves what?
Spatial resolution
Flatfielding is performed to do what?
Correct nonuniform pixel response
The primary purpose of AAPM TG-18 guidelines is to:
Evaluate digital display performance
Under photopic conditions, the eye is most sensitive to which wavelength?
555 nm
Radiographers should evaluate digital images from what viewing position?
Straight on to the display
The aperture ratio of an LCD refers to what?
Percentage of pixel area transmitting light
Image lag refers to what imaging artifact?
Residual signal from a prior exposure
Luminance measurements of digital displays are performed using what device?
Photometer
Which unit measures luminous flux?
Lumen
Ambient lighting in reading rooms should be kept low primarily to:
Reduce image contrast loss
Modern LED monitors are actually what type of display?
LCD displays with LED backlighting
Window and level adjustments are important because:
The eye sees only about 30 gray levels
What is a major advantage of LED backlighting compared with fluorescent backlighting?
Reduced power consumption