Blooming and Anti-Blooming Correction

Blooming and Anti-Blooming Correction

When the line sensor is saturated from excessive illumination and cannot accumulate more charges, the overloaded pixels transfer some of the excess charge to adjacent pixels − an effect termed blooming. Blooming leads to the corruption of the geometrical assignment of both the signal and the image generated by the line sensor. 

A line scan camera with an anti-blooming sensor can effectively dissipate the surplus charge arising from over-exposure by using a ‘drain gate’. The less exposed neighboring pixels are no longer corrupted. Over-exposures of up to 30-fold can be drained successfully, depending on the pixel frequency and spectral range of the line sensor.

Example: Line Scan Camera without Anti-blooming

Line scan camera signal from a bar code using a midtone incident light and the SK2048U3JR line scan camera without an anti-blooming sensor. 

The following example shows how a standard camera reacts to overexposure.

Anti-Blooming

Standard Line Signal

Line signal with enhanced illumination of the central range.

Anti-Blooming

Zoom into the image

Zoom of the signal depicted in the first image showing the steep signal edge

Anti-Blooming

Blooming begins

Extension of the integration time by a factor of 3.81 produces edges that are no longer vertical and have noticeable shoulders – the blooming of the sensor has begun.

Anti-Blooming

Blooming: severe signal and data corruption

Over-exposure caused by too large an integration time leads to severe signal and data corruption when using line scan cameras without antiblooming.

Anti-Blooming

Extreme Blooming

Extreme over-exposure floods the dark pixels of the sensor, the offset control is disturbed and the line scan camera produces an attenuated signal.