Sensor Output – Monochrome Vs RAW Bayer

Updated: Dec 22, 2020

We are looking for cameras for our application, we come across 3 types of camera modules

1. Monochrome camera modules

2. RAW Bayer camera modules

3. Color camera modules

Color camera modules is a derivation from the RAW Bayer imaging sensors. In case of color cameras, the camera module has an additional image signal processor on-board that integrates with the sensor and converts the RAW Bayer data from the sensor to viewable color data. We shall discuss on the Image Signal Processor in the further blocks.


The scope of this article is to introduce you to 2 types of sensors

1. Monochrome sensor

2. RAW Bayer sensor

Monochrome Sensor


As we know, the sensor is made up of pixel. Each pixel has a corresponding microlens on top of it that focuses the photos onto the active region for more efficiency. When the exposure begins, each pixels gets exposed to photons which are converted to electrical charge and quantified and then stored as numerical value.


In case of monochrome, all wavelength of light is allowed into each pixel. The effective numerical value stored essentially is a measure of the quantity of light. It does not have the necessary architecture to distinguish and measure color information.


Thus, monochrome sensor only provides us with luminescence data.


RAW Bayer Sensor


The underlying architecture of RAW Bayer sensor is same as that of the monochrome sensor. However, it does have an additional Color Filter Array integrated as a part of the microlens. The most successful color filter array is the Bayer Pattern. Bayer Pattern uses alternating rows of red-green and green-blue filter as shown in the below image.



The color filter array enables us to capture the color information in the scene as the red filter allows only red wavelength to pass, green filter allows only green wavelength to pass and blue filter allows only blue wavelength to pass. Thus, we have information red, green and blue in the scene which can be interpolated to get color image.


RAW Bayer vs Monochrome

 

→ Monochrome sensor does not give us color information of the scene.

→ However, since it does not filter out any wavelength, the amount of light entering

the pixel is more. Thus, monochrome sensors have more sensitivity.

→ Moreover, monochrome sensors do not require any additional interpolation or

processing. Thus, monochrome cameras are relatively easier to develop.

 

→ RAW Bayer sensors bring color information of the scene. Thus, we have the

complete image at hand. We can always get monochrome data out of color data but

vice-versa is not possible.

→ However, RAW Bayer sensors needs additional processors and circuitry to be

able to proper color data. Thus, developing a color camera is more complex that

monochrome camera.

→ Owing the color filter array, the sensitivity of the color camera is lower than

monochrome camera as each pixel accepts 1/3 of light.

 

As you can see, both monochrome and RAW Bayer sensors have their own benefits and challenges. Based on the application and use-case of the camera, we shall be able to select the right sensor.


We at Regami shall be glad to address any queries you have.


Cheers

Sarvesh Rajagopal

sarvesh@regami.solutions