DIS Image Processing & Enhancement 2 — Questions and Answers
Question 1: Which histogram equalization technique adapts the contrast enhancement to localized regions of an image rather than the entire image?
- Global histogram equalization
- CLAHE (Contrast Limited Adaptive Histogram Equalization) (Correct answer)
- Linear contrast stretching
- Gamma correction
Correct answer: CLAHE (Contrast Limited Adaptive Histogram Equalization)
CLAHE divides the image into tiles and applies histogram equalization locally while limiting contrast amplification to prevent noise over-enhancement.
Question 2: When applying an unsharp mask for sharpening, what does the 'amount' parameter control?
- The size of the blurred copy subtracted from the original
- The strength of the edge enhancement applied (Correct answer)
- The threshold below which pixels are not sharpened
- The color channel used for sharpening
Correct answer: The strength of the edge enhancement applied
The 'amount' parameter in unsharp masking controls how strongly the edge detail is boosted relative to the blurred reference image.
Question 3: A noise reduction filter that replaces each pixel with the middle value of its neighborhood is called a:
- Mean filter
- Gaussian blur
- Median filter (Correct answer)
- Bilateral filter
Correct answer: Median filter
The median filter replaces each pixel with the median of surrounding pixels, making it highly effective at removing salt-and-pepper noise while preserving edges.
Question 4: In frequency domain image processing, what does applying a low-pass filter accomplish?
- Enhances fine details and edges
- Removes low-frequency gradients from the image
- Blurs the image by attenuating high-frequency components (Correct answer)
- Increases the dynamic range of pixel values
Correct answer: Blurs the image by attenuating high-frequency components
A low-pass filter allows low frequencies (smooth tones) to pass while blocking high frequencies (edges and noise), resulting in a blurred image.
Question 5: Which blending mode in image compositing multiplies the pixel values of two layers, always resulting in a darker image?
- Screen
- Overlay
- Multiply (Correct answer)
- Dodge
Correct answer: Multiply
Multiply mode multiplies the normalized pixel values of two layers, darkening the result since multiplying values less than 1 always produces a smaller value.
Question 6: What is the purpose of a 'dust and scratches' filter in image restoration?
- Sharpens fine grain structure in the image
- Detects and removes small blemishes by blending with surrounding pixels (Correct answer)
- Converts color noise into luminance noise
- Adds a vintage texture to the image
Correct answer: Detects and removes small blemishes by blending with surrounding pixels
The dust and scratches filter identifies small anomalies (spots, lines) and replaces them with interpolated data from surrounding pixel areas.
Question 7: When performing frequency separation retouching, the low-frequency layer contains:
- Fine texture and skin pores
- Color, tone, and volume information (Correct answer)
- Sharpness and micro-contrast
- Noise and grain patterns
Correct answer: Color, tone, and volume information
In frequency separation, the low-frequency layer holds broad tonal variations, color, and volume, while the high-frequency layer holds fine texture details.
DIS Image Processing & Enhancement 2
Which histogram equalization technique adapts the contrast enhancement to localized regions of an image rather than the entire image?