SUPPORT > SIDE SCAN IMAGERY > GAIN & CONTRAST SETTINGS

When operating your sonar, the adjustments you will make to the gain and contrast controls in the software are critical in achieving good side scan imagery.

This section examines the function and purpose of these controls...

Gain

The software gain control is similar to the volume control on a home hi-fi system, or the brightness control on a television. The gain control sets how the incoming scan-lines of data (from the sonar hardware) map onto the sonar display's colour palette.

• Increasing the gain value will make all areas of the display image appear brighter, while decreasing it will make the whole image appear darker.
• For general operation, a gain value of 30% (-28dB) is recommended.

Contrast

The function of the contrast control is slightly more complex to understand than that of the gain control. The contrast value sets the colour palette range that the incoming signal will be stretched or shrunk to fit.

• A lower contrast value means that the image will transition from dark to bright colours more quickly than a higher contrast value.
• For general operation, a contrast value of 30% (38dB) is recommended, but can be reduced to 25% to enhance shadows and submerged targets.

The best way to understand the operation of the Gain and Contrast controls is to experiment with these values while scanning the sonar over a known area of seabed.

Generally, having set the operational range of the sonar, you should then set the gain to a level where the background noise is just visible. This should ensure that quiet signals are visible at the extremities of the display, whilst the central mid-water areas and seabed profile have good definition.

Then, when scanning, adjust the contrast to give the desired sharpness of targets - lowering the contrast will make echoes appear brighter, while keeping shadows dark.