OpenCV Questions and Answers – Capturing Frames

This set of OpenCV Multiple Choice Questions & Answers (MCQs) focuses on “Capturing Frames”.

1. Which flag is used to access the image generator properties?
a) CV_CAP_OPENNI_IMAGE_GENERATOR
b) CV_CAP_IMAGE_GENERATOR
c) CV_CAP_OPENNI_DEPTH_GENERATOR
d) CV_OPENNI_DEPTH_GENERATOR
View Answer

Answer: a
Explanation: CV_CAP_OPENNI_IMAGE_GENERATOR is a flag for access to the image generator properties, while CV_CAP_OPENNI_DEPTH_GENERATOR is a flag for access to the depth generator properties. This flag value is assumed by default if neither of the two possible values of the property is not set.

2. What is depth map?
a) A depth map is a grayscale image in which each pixel value is the estimated distance from the camera to a surface
b) A depth map is a BGR image in which each pixel value is the estimated distance from the camera to a surface
c) A depth map is a YBR image in which each pixel value is the estimated distance from the camera to a surface
d) A depth map is a RGB image in which each pixel value is the estimated distance from the camera to a surface
View Answer

Answer: a
Explanation: A depth map is a grayscale image in which each pixel value is the estimated distance from the camera to a surface. Specifically, an image from the CV_CAP_OPENNI_DEPTH_MAP channel gives the distance as a floating-point number of millimeters.

3. Which of the following flag is used to access the depth generator properties?
a) CV_CAP_OPENNI_IMAGE_GENERATOR
b) CV_CAP_IMAGE_GENERATOR
c) CV_CAP_OPENNI_DEPTH_GENERATOR
d) CV_OPENNI_DEPTH_GENERATOR
View Answer

Answer: c
Explanation CV_CAP_OPENNI_DEPTH_GENERATOR is a flag for access to the depth generator properties. This flag value is assumed by default if neither of the two possible values of the property is not set, while CV_CAP_OPENNI_IMAGE_GENERATOR is a flag for access to the image generator properties.
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4. A depth map is a grayscale image in which each pixel value is the estimated distance from the camera to a surface.
a) True
b) False
View Answer

Answer: a
Explanation: A depth map is a grayscale image in which each pixel value is the estimated distance from the camera to a surface. Specifically, an image from the CV_CAP_OPENNI_DEPTH_MAP channel gives the distance as a floating-point number of millimeters.

5. Which of the following is TRUE about point cloud map?
a) A point cloud map is a grayscale image in which each color corresponds to a spatial dimension (x, y, or z)
b) A point cloud map is an Alpha image in which each color corresponds to a spatial dimension (x, y, or z)
c) A point cloud map is a color image in which each color corresponds to a spatial dimension (x, y, or z)
d) A point cloud map is a CMYK image in which each color corresponds to a spatial dimension (x, y, or z)
View Answer

Answer: c
Explanation: A point cloud map is a color image in which each color corresponds to a spatial dimension (x, y, or z). Specifically, the CV_CAP_OPENNI_POINT_CLOUD_MAP channel yields a BGR image where B is x (blue is right), G is y (green is up), and R is z (red is deep), from the camera’s perspective. The values are in meters.

6. A valid depth mask shows whether the depth information at a given pixel is believed to be valid (shown by a non-zero value) or invalid (shown by a value of zero).
a) True
b) False
View Answer

Answer: a
Explanation: A valid depth mask shows whether the depth information at a given pixel is believed to be valid (shown by a non-zero value) or invalid (shown by a value of zero). For example, if the depth camera depends on an infrared illuminator (an infrared flash), then depth information is invalid in regions that are occluded (shadowed) from this light.

7. Which of the following is TRUE about disparity map?
a) A disparity map is a RGB image in which each pixel value is the stereo disparity of a surface.
b) A disparity map is a grayscale image in which each pixel value is the non-stereo disparity of a surface.
c) A disparity map is a grayscale image in which each pixel value is the stereo disparity of a surface.
d) A disparity map is a Color Video in which each pixel value is the stereo disparity of a surface.
View Answer

Answer: c
Explanation: A disparity map is a grayscale image in which each pixel value is the stereo disparity of a surface. Disparity map refers to the apparent pixel difference or motion between a pair of stereo images.
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8. Which of the following flag is used to provides floating point disparity values in pixels?
a) CV_CAP_OPENNI_DISPARITY_MAP
b) CV_CAP_OPENNI_DISPARITY_MAP_32F
c) CV_CAP_OPENNI_DEPTH_MAP
d) CV_CAP_OPENNI_POINT_CLOUD_MAP
View Answer

Answer: b
Explanation:The CV_CAP_OPENNI_DISPARITY_MAP_32F provides floating point disparity values in pixels, while CV_CAP_OPENNI_DISPARITY_MAP retrieves disparity data in an 8bit integer format and CV_CAP_OPENNI_DEPTH_MAP retrieves depth values in mm.

9. Which flag registers the remapping depth map to image map by changing depth generator’s view point (if the flag is “on”) or sets this view point to its normal one (if the flag is “off”)?
a) CV_CAP_PROP_ REGISTRATION
b) CV_CAP_PROP_OPENNI_BASELINE
c) CV_CAP_PROP_FPS
d) CV_CAP_PROP_OPENNI_REGISTRATION
View Answer

Answer: d
Explanation: CV_CAP_PROP_OPENNI_REGISTRATION – Flag that registers the remapping depth map to image map by changing depth generator’s view point (if the flag is “on”) or sets this view point to its normal one (if the flag is “off”). The registration process’s resulting images are pixel-aligned, which means that every pixel in the image is aligned to a pixel in the depth image.
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10. Which of the following is the default output mode of CV_CAP_PROP_OPENNI_OUTPUT_MODE flag?
a) CV_CAP_OPENNI_VGA_30HZ
b) CV_CAP_OPENNI_SXGA_15HZ
c) CV_CAP_OPENNI_SXGA_30HZ
d) CV_CAP_OPENNI_SXGA_40HZ
View Answer

Answer: a
Explanation: CV_CAP_OPENNI_VGA_30HZ is the default output mode of CV_CAP_PROP_OPENNI_OUTPUT_MODE (image generator returns images in VGA resolution with 30 FPS), CV_CAP_OPENNI_SXGA_15HZ (image generator returns images in SXGA resolution with 15 FPS) and CV_CAP_OPENNI_SXGA_30HZ (image generator returns images in SXGA resolution with 30 FPS, the mode is supported by XtionPRO Live).

11. Which of the following is TRUE about depth generator’s maps resolution?
a) Depth generator’s maps are always in VGA resolution.
b) Depth generator’s maps are always in SXGA resolution.
c) Depth generator’s maps are always in XGA resolution.
d) Depth generator’s maps are always in UXGA resolution.
View Answer

Answer: a
Explanation: Depth generator’s maps are always in VGA (Video Graphics Array) resolution. SXGA stands for Super Extended Graphics Array while UXGA stands for Ultra Extended Graphics Array.

12. What is the full Form of WHUXGA?
a) Wide Hex Ultra Extended Graphics Array
b) Wide Hex Ultimate Extended Graphics Array
c) Wide Hexadecimal Ultra Extended Graphics Array
d) Wide Hex Ultra Extended Graph Array
View Answer

Answer: a
Explanation: The Full Form of WHUXGA is Wide Hex Ultra Extended Graphics Array. WHUXGA is also called a “Hyper XGA” resolution. It has screen resolution of 7680×4800 pixels, which is 16 (hex) times the total number of pixels in the WUXGA standard (1920×1200).

13. What is the full Form of QXGA?
a) Quadratic eXtended Graphics Array
b) Quadrium eXtended Graphics Array
c) Quad eXtended Graphics Array
d) Quad eXtendedable Graphics Array
View Answer

Answer: c
Explanation: The Full Form of QXGA is Quad eXtended Graphics Array. QXGA is a display resolution standard with a 4:3 aspect ratio that measures 2048 x 1536 pixels. It is four times that of XGA (Extended Graphics Array).

14. What is the full Form of WQSXGA?
a) Wide Quad Simple Extended Graphics Array
b) Wide Quad Super Extended Graphics Array
c) Wide Quad Super Extendedable Graphics Array
d) Wide Quadrium Super Extended Graphics Array
View Answer

Answer: b
Explanation: The Full Form of WQSXGA is Wide Quad Super Extended Graphics Array. WQSXGA has screen resolution of 3200×2048 pixels, which is a wide-screen version of the QSXGA standard (2560×2048).

15. What is the full Form of EGA?
a) Extended Graphics Adapter
b) Enhanced Graphics Array
c) Enhanced Graphics Adapter
d) Extended Graphics Array
View Answer

Answer: c
Explanation: The Full Form of EGA is Enhanced Graphics Adapter. EGA (Enhanced Graphics Adapter) had screen Resolution of 640×350. The EGA was superseded by VGA (Video Graphics Array) three years later which has resolution of 640 x 480.

Sanfoundry Global Education & Learning Series – OpenCV.

To practice all areas of OpenCV, here is complete set of Multiple Choice Questions and Answers.

If you find a mistake in question / option / answer, kindly take a screenshot and email to [email protected]

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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