Imaging system response linearization and shading correction

Shading correction of image sensors is a very important operation in visual inspection applications. The generation and application of shading correction with and without imaging system response linearization is discussed and demonstrated. The linearization is achieved by subtracting the dark current image and by applying a lookup table operation. The content of the lookup table is obtained by fitting an analytical function to the measured system response. The linearization enables the shading correction to be a linear operation. The quality of the linearization and the shading correction was evaluated using statistical parameters of the processed images. The results showed a substantial decrease in the standard deviation of the gray level distribution of uniform reference images.