How are the gain and offset settings used? Why should I use default settings in Gain and Offset?

A bulk of digital imaging lies in converting intensities of light (from an image) into values of digital numbers. Each pixel on the CCD reads an intensity of light by converting photons of light into electrons (charge). The charge on each pixel is directly proportional (linear) to the amount of light that hits the pixel. Brighter light will create a higher charge and, conversely, dimmer light will create less charge. Let us define the charges out of the CCD pixels (analog electric current) as the input. The inputs will range from a black value (no light, no charge) to a white value (bright, full charge).

The outputs from our camera (that are displayed in QCapture) are digital numbers representing the values of the electric charge from the inputs. The digital numbers are 8, 10 or 12 bit numbers ranging from a black value (no light, no charge) at digital value 0 to a white value (full light, full charge) at digital value [(2^n) -1] where n is the bit depth. The challenge here is to create a digital output that accurately represents the analog input; this is completed by mapping the full analog input range (from black to white) to the full digital output range (again, black to white).

In our cameras, the input from the CCD (electric charge) is amplified and then added to an offset. This final analog value is converted into a digital number by an Analog to Digital Converter (ADC). Referring to Figure 1, you can see how the default gain and offset map the full analog input range to the full digital range. As shown in the pdf, changing the gain changes the 'width' of the analog input range in the digital scale and changing the offset shifts the analog input range up and down the digital scale.

The default values are optimum because they map the full analog input range to the full digital output range. In this configuration, the camera operates at the highest possible dynamic range and signal to noise ratio.

For more information please refer to the document titled 'Digital Camera Data Processing' in the 'Documents' section of our site.