Image Acquisition Flashcards
What does a light sensor chip do?
Record all the data in a very short space of time
What is the camera covered with and what do they do?
The camera sensor is covered with tiny individual light-sensitive cells, each of which can measure the amount of light that falls on it. The cells react to the light that falls on them and then reports it to the microprocessor. This would result in black and white photos so instead the light ‘seen’ by the camera is split into the three primary colours which can then be used to create an accurate image.
What is a Bayer filter?
This is a grid of coloured filters that sit over the sensor with red, green and blue elements over the individual pixels and they will only allow the respective colour through.
What is the human eye most sensitive to?
The human eye is most sensitive to green light which largely determines how bright an image looks, there are twice as many green pixels as there are blue or red.
What is CMOS?
Complementary Metal Oxide Semi Conductor
What is DSLR?
Digital single lens reflex
What does the lens do?
Focuses light on the sensor
What does the sensor do?
Turns light into a recordable image by converting the light intensity into an electrical signal which forms the digital image.
What does the DSP do?
DSP unit performs some basic image processing before the image is saved. Eg white balance to improve brightness of the image
What is CFA?
Colour filter array
What is DSP?
Digital signal processing unit?
What do photosites do?
Detect the intensity of the light
How is infrared light dealt with?
Infrared light is filtered out through the infrared filter.
What does the CFA do?
The colour filter array compensates for the colour blindness filter of the sensor
What type of lens do digital cameras tend to have?
Compound lenses
What are compound lenses?
They consist of a number of lenses bonded together.
What is the purpose compound lenses
This is done to avoid chromatic and geometric apparitions (distortions of image).
What is the purpose of compound lenses
This is done to avoid chromatic and geometric apparitions (distortions of image).
When an object is closer to the lens where should the sensor be?
- If the object is closer to the lens, therefore closer to the camera, you need to move the sensor further away from the lens.
- If the object is closer than the focal length to the camera you won’t be able to get a crisp clear image.
What is the equation for object image relation? (Thin lens equation!)
1/s + 1/s’ = 1/f
What does Y relate to?
Height of object
What does Y’ relate to?
Height of image
What does S relate to?
Distance of object from lens
What does S’ relate to?
Distance of focused image from lens
What does F relate to?
The focal length
What is the equation for magnification?
m = - y’ / y
m = - s’/s
What does the infrared filter do?
The infrared filter reduces the amount of IR that reaches the sensor.
Once the light is passed through the infrared filter where does it go next?
It passes through the colour filter array
What are the two common configurations of the CFA?
- Stripe
- Bayer (Most common)
Where does light go after the CFA?
The sensor
What is the path light takes in a camera?
Lens –> Infrared filter –> Colour filter array –> Sensor
What are photodiodes
Semiconductor devices that generate an electrical charge in proportion to the number of photons that reach them
What are the two main types of sensors/detectors?
- Charged couple device (CCD)
- Complementary metal oxide semiconductor (CMOS)
What are the advantages of the charged couple device?
- High signal/noise ratio
- Low noise
- Whole surface is light sensitive
What are the disadvantages of charged couple device?
- Higher power consumption
- Slower speed
- On-chip peripheral circuits are difficult to manufacture.
What are the advantages of CMOS?
- More dominant technology
- Simple and cheaper to manufacture
What is the drawback of CMOS?
Relatively high noise
How are green values interpolated?
Bilinear interpolation - done in both the horizontal and vertical direction
