HDR Imaging Techniques & Technologies 3 â Questions and Answers
Question 1: In HDR photography, what is 'ghost removal' and why is it necessary?
- Eliminating lens flare artifacts
- Correcting misaligned moving objects between multi-exposure brackets (Correct answer)
- Removing hot pixels from sensors
- Reducing noise in shadow regions
Correct answer: Correcting misaligned moving objects between multi-exposure brackets
Ghost removal algorithms detect and correct objects that moved between bracketed exposures, preventing transparent double-image artifacts in the merged HDR result.
Question 2: Which color space is specifically designed to encompass the full range of human visible colors and is used as a reference in HDR mastering?
- sRGB
- Rec. 709
- ICtCp
- BT.2020 (Correct answer)
Correct answer: BT.2020
BT.2020 (Rec. 2020) defines a very wide color gamut covering approximately 75.8% of the CIE 1931 color space, serving as the standard container for HDR content mastering.
Question 3: What is the function of the OOTF (Opto-Optical Transfer Function) in an HDR system?
- Converts scene light to display light, accounting for viewing environment (Correct answer)
- Converts digital code values to scene luminance
- Maps display signal to optical output only
- Defines color gamut boundaries
Correct answer: Converts scene light to display light, accounting for viewing environment
The OOTF is the end-to-end transfer function that maps scene luminance to display luminance, incorporating the effect of the viewing environment on perceived contrast.
Question 4: In dual-native ISO sensors, how does HDR capture benefit?
- It doubles the frame rate
- It allows switching between two sensitivity levels to blend highlights and shadows (Correct answer)
- It increases color bit depth automatically
- It removes the need for tone mapping
Correct answer: It allows switching between two sensitivity levels to blend highlights and shadows
Dual-native ISO sensors blend data from two optimized analog gain stages, capturing clean highlights at low ISO and low-noise shadows at high ISO in a single exposure.
Question 5: What is 'absolute luminance metadata' and how does it help HDR displays?
- Data that locks color gamut to sRGB
- Values specifying the actual cd/m² levels of scene content for display calibration (Correct answer)
- A flag that enables 10-bit output
- Information about the camera sensor size
Correct answer: Values specifying the actual cd/m² levels of scene content for display calibration
Absolute luminance metadata communicates the minimum, maximum, and average light levels of content so HDR displays can render it with accurate brightness and without clipping.
Question 6: Which artifact commonly appears in poorly implemented local tone mapping of HDR images?
- Chromatic fringing
- Halo artifacts around high-contrast edges (Correct answer)
- Reduced bit depth banding
- Temporal flickering only
Correct answer: Halo artifacts around high-contrast edges
Local tone mapping can produce halosâbright or dark rings around high-contrast edgesâwhen the local processing radius is too large or the compression too aggressive.
Question 7: How does 'exposure fusion' differ from traditional HDR merge-then-tone-map pipelines?
- It skips the exposure bracketing step
- It blends multiple exposures directly in display-referred space without constructing an HDR intermediate (Correct answer)
- It uses only a single raw file
- It requires a calibrated spectrophotometer
Correct answer: It blends multiple exposures directly in display-referred space without constructing an HDR intermediate
Exposure fusion combines well-exposed regions from different bracketed images using quality metrics, bypassing the explicit HDR float merge and tone mapping steps.
HDR Imaging Techniques & Technologies 3
In HDR photography, what is 'ghost removal' and why is it necessary?