ISF Video Standards & Signal Processing 4 — Questions and Answers
Question 1: What is the function of a comb filter in analog video processing?
- To separate the luma (Y) and chroma (C) components of a composite signal (Correct answer)
- To remove 60 Hz hum from a video signal
- To sharpen horizontal edges by boosting high-frequency luma
- To convert component video to composite format
Correct answer: To separate the luma (Y) and chroma (C) components of a composite signal
A comb filter exploits the phase relationship between luma and chroma in composite video to separate them with minimal cross-contamination (cross-color and dot crawl).
Question 2: What does EOTF stand for, and what does it describe?
- Electro-Optical Transfer Function; the mapping from signal code values to display light output (Correct answer)
- Electro-Optical Transfer Function; the mapping from scene light to camera signal
- Extended Output Transfer Format; a container for HDR metadata
- Electro-Optical Transfer Function; the gamma applied during video encoding
Correct answer: Electro-Optical Transfer Function; the mapping from signal code values to display light output
EOTF (Electro-Optical Transfer Function) describes how a display device converts electrical signal values into emitted light, the inverse of the OETF applied at capture.
Question 3: In a vectorscope display, what does a dot plotted at the center of the graticule indicate?
- The signal has no chroma—it is neutral (black, gray, or white) (Correct answer)
- The signal's chroma phase is perfectly aligned with the burst reference
- The luma level is at 50 IRE
- The signal is clipping in both I and Q channels
Correct answer: The signal has no chroma—it is neutral (black, gray, or white)
A vectorscope plots chroma as a dot whose angle represents hue and whose distance from center represents saturation; a dot at center means zero saturation (achromatic).
Question 4: Which color space is defined by the ITU-R BT.709 standard and is the reference for HDTV production?
- A D65 white point with specific red, green, and blue primaries and a gamma of approximately 2.4 (Correct answer)
- A D50 white point with wide-gamut primaries and a PQ transfer function
- The same primaries as sRGB but with a different transfer function
- DCI-P3 primaries with a D65 white point
Correct answer: A D65 white point with specific red, green, and blue primaries and a gamma of approximately 2.4
BT.709 specifies R/G/B primaries, a D65 white point, and an OETF with an effective display gamma near 2.4, serving as the standard for HDTV and most streaming content.
Question 5: What artifact is caused by incorrect deinterlacing when converting interlaced video to progressive?
- Combing, where horizontal lines from two different fields appear at the same time causing jagged edges on moving objects (Correct answer)
- Mosquito noise around sharp edges due to compression
- Banding in smooth gradients due to insufficient bit depth
- Halation around bright highlights due to display phosphor bleed
Correct answer: Combing, where horizontal lines from two different fields appear at the same time causing jagged edges on moving objects
Combing occurs when a naive deinterlacer blends both fields of a frame containing motion, producing a comb-like edge artifact on moving objects.
Question 6: What is the purpose of the color burst signal in analog composite video?
- To provide a phase and frequency reference so the decoder can extract chroma correctly (Correct answer)
- To set the black level reference for the luma signal
- To synchronize the horizontal sweep of the display
- To indicate the start of active video after the blanking interval
Correct answer: To provide a phase and frequency reference so the decoder can extract chroma correctly
The color burst is a short burst of the subcarrier frequency placed on the back porch of each horizontal sync pulse, giving the decoder a reference to decode chroma phase and amplitude.
Question 7: What does 'color volume' mean in the context of HDR displays?
- The combination of color gamut and luminance range a display can simultaneously achieve (Correct answer)
- The total number of colors in a display's color lookup table
- The physical size of the display's color filter array
- The dynamic range of the audio signal paired with HDR video
Correct answer: The combination of color gamut and luminance range a display can simultaneously achieve
Color volume describes the full 3D space of colors a display can produce, accounting for how gamut coverage changes at different luminance levels.
ISF Video Standards & Signal Processing 4
What is the function of a comb filter in analog video processing?