Multimedia Forensics
Multimedia Forensics Quiz Crafted by-
Dr. Surbhi Mathur
Senior Assistant Professor
Institute of Forensic Science
Gujarat Forensic Science University, Gujarat, INDIA
Introduction about Multimedia Forensics
Multimedia forensics can be defined as the science that tries, by only examining a particular digital asset, to give an assessment on such content and to extract information that can be useful to address and support and investigation linked to the scene represented in that specific digital document. Multimedia forensics includes a set of scientific techniques proposed for the analysis of multimedia signals (audio, videos, images) to identify the acquisition device that produced the data, aim at validating the integrity of the content, and retrieving information from multimedia signals.
Ques 1. In Joint Photographic Experts Group (JPEG), a grayscale picture is divided into blocks of:
A) 7X7
B) 8X8
C) 6X6
D) 10X10
Answer - B)8X8
Explanation: - JPEG features an adjustable compression ratio that lets a user determine the quality & size of the final image. Attempting to compress an entire image would not yield the optimal result. Therefore, JPEG divides the image to matrices of 8X8 pixel blocks. This allows the algorithm to take advantage of the fact that similar colors tend to appear together in small parts of an image.
Ques 2. A sampling of analog signals can be done using:
A) Source & Filter theorem
B) Nyquist Theorem
C) Bernoulli's Theorem
D) Helmholtz’s Theorem
Answer: -B) Nyquist Theorem
Explanation: - Nyquist theorem or sampling theorem states that an analog signal waveform can be converted into digital by sampling the analog signal at equal time intervals. The sampling rate must be equal to or greater than, twice the highest frequency component in the analog signal.
Ques 3. Unit of calculating signal to noise ratio (SNR):
A) Hertz (Hz)
B) Decibels (dB)
C) Bytes
D) Bit
Answer: -B) Decibels (dB)
Explanation: - SNR is a measure used in science & engineering that compares the level of the desired signal to the level of background noise. SNR is defined as the ratio of signal power to noise power expressed in decibels. A ratio higher than 1:1 indicates more signal than noise.
Ques 4. The narrower aperture size of a video camera leads to:
A) Shallow depth of field
B) Deeper depth of field
C) Decrease depth of focus
D) Decrease shutter speed
Answer: -B) Deeper depth of field
Explanation: - Aperture can be defined as the opening in a lens through which light passes to enter the camera. Aperture can add dimension to your photos by controlling the depth of the field. The depth of field is the amount of your photograph that appears sharp from front to back. A large aperture results in a reduced depth of field and narrow aperture results in a deeper depth of field.
Ques 5. The false coloring technique commonly used for remote sensing operations:
A) Pseudo colors
B) Choropleth
C) Density slicing
D) Thermography
Answer: -C) Density slicing
Explanation: - Density slicing is a digital data interpretation method used in the analysis of remotely sensed imagery to enhance the information gathered from an individual brightness band. It is done by dividing the range of brightness in a single band into intervals, then assigning each interval to a color.
Ques 6. When a 4-inch lens is focused on infinity at a diaphragm setting of 3.5, all objects at approx. 75 feet to infinity, appear to be in sharp focus. What will be its hyperfocal distance?
A) 75 feet
B) 37.5 feet
C) 150 feet
D) 25 feet
Answer: -A)75 feet
Explanation: - Hyperfocal distance is the closest distance at which a lens can be focused while keeping objects at infinity acceptably sharp. When the lens is focused at the distance, all objects at distances from half of the hyperfocal distance out to infinity will be acceptably sharp.
Ques 7. Type of sound representing high frequencies by shaping the vocal folds:
A) Creaking
B) Falsetto
C) Murmur
D) Whisper
Answer: -B) Falsetto
Explanation: - Falsetto is the vocal register occupying the frequency range just above modal voice register & overlapping with it by approximately one octave. It is produced by the vibration of the ligamentous edges of the vocal cords, whole or in part. Commonly cited in the context of singing, falsetto, a characteristic of phonation by both sexes is also one of 4 main spoken vocal registers recognized by speech pathology.
Ques 8. What is the term which represents the use of links between all sorts of multimedia information?
A) Hypertext
B) Hypermedia
C) Media card
D) Hyper card
Answer: -B) Hypermedia
Explanation: - Hypermedia is an extension to what is known as hypertext, or the ability to open new web pages by clicking text links on a web browser. Hypermedia extends upon this by allowing the user to click images, movies, graphics, and other media apart from text to create a nonlinear network of information. The term was coined by Fred Nelson in 1965.
Ques 9. For Dynamic range ratio of multimedia file, the lower limit is determined by:
A) Brightness
B) Contrast
C) Saturation
D) Noise
Answer:-D) Noise
Explanation: - Dynamic range is an expression of the ratio of the largest signal a device can pass to the device's noise floor. It is the ratio between the largest and the smallest values that a certain quantity can assume. It is often used in the context of signals, like sound and light.
Ques 10. Audio editing was done without changing the overall dynamic values of the audio file:
A) Normalization
B) Enhancement
C) Chopping
D) Transformation
Answer: -A) Normalization
Explanation: - Audio normalization is the application of a constant amount of gain to an audio recording to bring the amplitude to a target level. Because the same amount of gain is applied across the entire recording, the signal to noise ratio and relative dynamics are unchanged. Normalization is one of the functions commonly provided by a digital audio workstation.
Ques 11. In Voice Over IP, Term SIP stands for:
A) Session Initiation Process
B) Session Interactive Process
C) Session Interactive Protocol
D) Session Initiation Protocol
Answer:-D) Session Initiation Protocol
Explanation: - The Session Initiation Protocol (SIP) is a signaling protocol used for initiating, maintaining, and terminating real-time sessions that include voice, video, and messaging application. SIP is used for signaling and controlling multimedia communication sessions in the application of internet telephony for voice and video calls, in private IP telephone systems, in instant messaging over Internet Protocol (IP) networks as well as mobile phone calling over LTE.
Ques 12. The word "caught" is an example of which type of vowel?
A) Mid, back & rounded
B) Front, back & rounded
C) Low, back & unrounded
D) Low, back & rounded
Answer: -A) Mid, back & rounded
Explanation: - The mid-back rounded vowel is a type of vowel sound, used in some spoken languages. Vowel height is mid, which means the tongue is positioned halfway between a close vowel and an open vowel. Vowel backness is back, which means the tongue is positioned back in the mouth without creating a constriction that would be classified as a consonant. Its roundedness is protruded, which means that the corners of the lips are drawn together, and the inner surfaces exposed.
Ques 13. The type of lens used in a video camera for multiplying the focal length of its lens without affecting the closest focus distance:
A) Macro lens
B) Zoom lens
C) Teleconverter lens
D) Normal lens
Answer: -C) Teleconverter lens
Explanation: - A teleconverter is a secondary lens mounted between a camera and a photographic lens which enlarges the central part of an image obtained by the objective lens. It multiplies focal length without affecting the closest focusing distance. These magnification factors come at the cost of reduced light transmission which reduces the effective minimum aperture of the lens in use.
Ques 14. Spatial filtering is used in the presence of:
A) Black noise
B) Gamma noise
C) Additive random noise
D) Exponential noise
Answer: - C) Additive random noise
Explanation: - Spatial filters can be effectively used to remove various types of noise in digital images. These spatial filters typically operate in small neighborhoods, and some can be implemented as convolution masks.
Ques 15. Lossy technique provide____________ when compared to lossless technique.
A) Lower compression ratio
B) Higher compression ratio
C) Similar compression ratio
D) None of the above
Answer: - B) Higher compression ratio
Explanation: - Lossy compression is used to compress audio, video, and images. Lossless compression is used to compress text, images, and sound. Typically, depending on the image, lossless compression ratios range from about 1.5:1 to 3:1. On the other hand, lossy compression techniques give compression ratios above 20:1 with virtually no loss in visual fidelity.
Ques 16. What is the highest frequency that is contained in the sampled digital signal?
A) 2Fs
B) Fs/2
C) Fs
D) 3Fs
Answer: -B) Fs/2
Explanation: -We know that, after passing the signal through an anti-aliasing filter, the filtered signal is sampled at a rate of Fs≥2B=>Fs/2. Thus, the maximum frequency of the sampled signal is Fs/2.
Ques 17. Enhancement technique that makes edges of images clearer and more distinct:
A) Median filtering
B) Pseudo coloring
C) Sharpening
D) Contrast stretching
Answer: -C) Sharpening
Explanation: - Image sharpening refers to any enhancement technique that highlights edges and fine details in an image. Image sharpening is widely used in printing and photographic industries for increasing the local contrast and sharpening the images.
Ques 18. The problem caused in the digital multimedia file due to improper sampling:
A) False contours
B) Aliasing
C) Chipping
D) Attenuation
Answer: -B) Aliasing
Explanation: - In signal processing and related disciplines, aliasing is an effect that causes different signals to become indistinguishable when sampled. It also often refers to the distortion or artifact that results when a signal reconstructed from samples is different from the original continuous signal.
Ques 19. To hide information inside a picture, what technology is used?
A) Bitmapping
B) Watermarking
C) Steganography
D) Root Kits
Answer: -C) Steganography
Explanation: - Steganography is the practice of concealing a file, message, image, or video within another file, message, image, or video. The word steganography comes from Greek steganographia, which combines the words steganos, meaning "covered or concealed", and graphia meaning "writing".
Ques 20. Multimedia files stored on a remote server are delivered to a client across the network using a technique known as:
A) Streaming
B) Download
C) Floating
D) Leaking
Answer: -A) Streaming
Explanation: - Streaming media is multimedia that is constantly received by and presented to an end-user while being delivered by a provider. There are 2 types of streaming techniques- progressive download and real-time streaming.