Color Filter Arrays
There are many types of color filter arrays, with the most common being invented by Dr. Bayer of Eastman Kodak. This color filter array — or the Bayer mosaic as it is more commonly referred to — utilizes a filter pattern that is half green, only a quarter red and a quarter blue. This is based on the fact that the human eye is more sensitive to the green luminance, illustrated in Figure 3.
Figure 3. A Resultant Bayer Mosaic
Sensor Processing Signal Chain
A sensor processing signal chain is generally developed to:
- Correct the pixel information from the CMOS sensor
- Convert the Bayer image to RGB
- Apply any color correction that may be required
Figure 4 shows the essential blocks of such a signal chain
Figure 4. A Sensor Processing Signal Chain
The Bayer to RGB conversion is the key standard function required in a sensor processing signal chain. This is also the most complex if implemented using a multi-tap filter.
Pixel correction and formatting is a function that is highly dependent on the image sesnor used, so this is generally a custom implementation. Color correction, while a simple function to implement in hardware, is complex as far as the determination of the correction factor.
Next let’s look at two implementations of a Bayer to RGB conversion algorithm. The operation of a design that brings together all of these functions to implement a complete image sensor processing chain will then be detailed, and this is verified and implemented in hardware with an Aptina CMOS sensor.
NEXT: Bayer to RGB (Bayer Demosaicing)
Page 2: next page
