What is 3A? Many freshmen may encounter this question when they first start their study in image processing. I found a blog(GM's blog) illustrate this question to beginners.

Autofocus(AF) algorithms

Camera’s autofocus automatically adjusts the distance between the camera lens and the CCD through the camera’s internal micro-driving motor to ensure that the image plane is projected onto the CCD’s image surface.

• Algorithms and formulas are based on perceptions of the human eyes, which are more sensitive to brightness/luminance compared to chrominance

• Y value in the colorspace of both YUV and YCrCb indicates the luminance

Autoexposure(AE)

General Scheme of AlgorithmPermalink

Auto exposure is to find an optimal exposure time at a given environment, which is typically made in the following steps.

Step 1: A pre-determined exposure value can be calculated as follow
Step 2: Convert the RGB values to Brightness B
Step 3: Derive a single number B*pre* from the brightness picture
Step 4: Calculate the optimum exposure EV*opt*

Autowhitebalance(AWB)(Color Balacing)

Human eyes adapt to varying illumination conditions that image sensor can’t, thus this needs to be computed

There are two ways of balancing

• Pre-computed sets
• Guess with an algorithm