Human Image Perception Flashcards
Light is focused where?
The retina
What does the visual cortex do?
Filtering, object recognition, edge detection, stereo fusion.
What is metamerism?
Light is a combination of wavelengths. Different combinations mat appear to be the same colour.
Briefly explain why SSIM is sometimes preferred to PSNR.
PNSR is the log of the ratio between the peak signal (image) power and the noise power. However, PSNR does not take into account of HVS.’
The structural similarity index was introduced in 2004 to predict the perceived quality of an image.
Why are, in the XYZ colour space, the difference RGB gamuts always represented as triangles.
- Each combination of RGB values, lie inside that triangle.
- The vertices of the triangle correspond to the 3 primary colours R,G,B.
Give two reasons why the YCbCr/YUV colour spaces are being used in image and video compression.
- YUV was used so that TV colour signals could be backward compatible with black and white TV sets.
- Most useful for producing grayscale images, because all the user has to do is to get rid of the U and V elements of the equation.
In the HSV colour space, what do they stand for?
Hue - the shade of colour
Saturation - colour depth
Value - brightness of the colour
HSV is less sensitive to what?
-> It’s less sensitive to higher frequencies.
-> It’s less sensitive to chrominance than luminance.
What’s weber’s law?
Related the perceived brightness of an object to the brightness of its background.
What’s the process of subsampling?
Noise is harder to see in what areas and why?
Noise is harder to see in textured areas due to reduction in contrast sensitivity at higher spatial frequencies.
HVS factors influence compression. Explain the influences.
- Contrast sensitivity drops as spatial frequency increases.
- Contrast sensitivity is less for chrominance than for luminance.
- Activity masking.
