the generic sensor
DESCRIPTION
The Generic Sensor. Problem: Since the sensor only records light intensity, we can’t differentiate between colors! Thus, digital cameras only record in black and white Solution: Color filtering, the most common form being the Bayer filter. - PowerPoint PPT PresentationTRANSCRIPT
The Generic Sensor
Each photosite converts lightwave energy into photo-electrons
Pixels in the output image are a measure of the number of photo-electrons recorded at each photo site
Light wellswells
SensorsSensors
Problem:Problem:
Since the sensor only records light intensity, Since the sensor only records light intensity, we can’t differentiate between colors!we can’t differentiate between colors!
Thus, digital cameras only record in black Thus, digital cameras only record in black and whiteand white
Solution:Solution:
Color filtering, the most common form being Color filtering, the most common form being the Bayer filterthe Bayer filter
1) Designates individual photosites to be either red, green, or blue (RGB)
2) Respective color filters are placed over each photosite
3) Thus, only the light energy corresponding to that color’s wavelength reaches the sensor
4) Thus the sensor can interpret the energy recorded at that photosite to be a measure of that certain color
The Bayer Sensor
Light wellswells
SensorsSensors
• Color offset- light not recorded at the same spot-Demosaic algorithms required to interpolate missing data
• Discards 2/3 of light information-3x longer shutter speed, 3x larger aperture, 3x higher ISO
DrawbackDrawback
s of…s of…
Actual Image
Raw Bayer Output
Demosiaced Bayer Output
Linear Scanning
Scans a scene with RGB linear sensors
Gets full light information
Slow, only works for static subjecs
Alternative Color Filtering Technologies
Bayer-like filters with different colors
RGBC
CYGM
Same problems as Bayer filter
Multi-shot approach
Take three shots, each with different color filter
Gets full light information
Only works for static subjects, since a moving scene would change between filter switches
Alternative Color Filtering Technologies in DevelopmentFoveon sensor
Uses vertically stacked RGB sensors
Collects all light at each location
Three-sensor
Commonly known as “3CCD”
Prism splits light, 3 sensors to record R,G,B
Color Temperature
Light sources can be approximated as “black bodies” of a certain temperature
Daylight: similar to 5000K black body (even light across the spectrum)Incandescent light: lower temperature (more red light, less blue)Shade/daylight: higher temperature (more blue light, less red)
Human vision system makes corrections for different light sourcesCameras aren’t so good at this
<- What we see
What cameras see ->(interpreting all wavelengths equally)
White Balancing
Auto-white balanceWhite balance presetColor temperatureCustom white balanceRAW adjustment
Last resort: color balance the JPEG