Image Quality

Image quality criteria can be divided into two categories: basic criteria that apply to all imaging system, image defects-some of this are unique to television images.

Basic criteria:

• Image definition. Definition is the degree of 'in-focus' appearance of the image. It is primarily determined by the shape of the transitions between dark and light areas of the picture. (EIA standard resolution test chart)
• Limiting resolution. (?)
• Gray scale. It can be specified by three parameters: 1. highlight brightness, the brightness of the brightest areas of the image; 2. contrast ratio, the ration of the brightness of the brightest areas of the image to the darkest; 3. gamma, the slope of the transfer characteristic of image brightness as a function of scene brightness.
• Signal-to-noise-ratio

Image defects:

• Flicker: when the frame rate is not high enough to cause the eye to see continuous image.
• Aliasing: sampling problem.
• Geometric distortion.
• Hum: ex. a horizontal hum bar moves vertically through the picture, interference caused by power source voltage.
• Ghost: a duplicate of the main mage, slightly displace from it.

Image quality factors:

1. sharpness: how to measure-use a bar pattern, use 'rise distance', the distance for the pixel level to go from 10% to 90% of its final value.
2. noise
3. color accuracy
4. tonal response & contrast
5. exposure accuracy
6. light
7. lens distortion: r_u = r_d + kr_d^3