Chapter Questions
Explain the importance of studying the HVS model for designing a multimedia system.
Explain the image formation process on the retina. How many different types of receptors are present in retina?
What is relative luminous efficiency of the HVS?
Define luminance and brightness. Even if two regions of an image have identical luminance values, they may not have same brightness. Why?
Define spatial frequencies and modulation transfer function. What is the sensitivity of the HVS to different spatial frequencies?
Consider a sinusoidal grating being viewed by an observer on a computer monitor. The distance between the observer and the monitor is $\mathrm{X}$, and the grating has a frequency of 2 cycles/degree. If the observer moves forward (towards the monitor) by $\mathrm{X} / 4$, what will be the new grating frequency? Assume a narrow angle vision.
Explain the frequency sensitivity of the HVS, and the Mach band effect.
Why do we need vision models? Explain a simple monochrome vision model.
What are the three perceptual attributes of color?
What are the three primary colors that are used for additive color reproduction? What is the basis of this model from the HVS perspective?
What are tristimulus values of a color?
Why is there a large number of color spaces? Compare the $\{R, G, B\},\{X, Y, Z\}$, and $\{\mathrm{Y}, \mathrm{I}, \mathrm{Q}\}$ color spaces.
What is the principle of subtractive color mixing? What are the three primaries typically used? What will be the reproduced color for i) yellow-green mixture, and ii) yellow-red?
Which method (subtractive or additive) of color reproduction is used in i) printing, ii) painting, iii) computer monitors, and iv) television monitors?
What is a chromaticity diagram? How does it help in color analysis? Which colors are found near the edges of the diagram? Which colors are found near the center?
Given a spectral color on the chromaticity diagram, how would you locate the coordinates of the color for different saturation value?
Determine the chromaticity values of i) green, ii) cyan, and iii) blue in CIE Spectral Primary coordinate systems.
The reference yellow in the NTSC receiver primary system corresponds to $R_N=G_N=1, B_N=0$. Determine the chromaticity coordinates of yellow in the CIE spectral primary system, and the $\{\mathrm{X}, \mathrm{Y}, \mathrm{Z}\}$ coordinates.
Repeat the previous problem for the reference white that corresponds to $R_N=G_N=B_N=1$.
A $2 \times 2$ color image is represented in CIE spectral primary system with the following $\mathrm{R}, \mathrm{G}$, and $\mathrm{B}$ values (in 8-bit representation).$$R=\left[\begin{array}{cc}20 & 220 \\150 & 80\end{array}\right], G=\left[\begin{array}{cc}20 & 220 \\150 & 30\end{array}\right], B=\left[\begin{array}{cc}220 & 20 \\120 & 160\end{array}\right]$$What are the colors of the four pixels? Convert the color image to a gray scale image. What would be the relative intensity of the gray pixels?
What is the temporal contrast (or flicker) sensitivity of the HVS? Does the sensitivity depend on the illumination level?