In CMOS image sensors the pixel response on exposure varies – more excessively than in CCD – from pixel to pixel. The image quality is also affected by a lot of external factors such as lighting, optics, temperature, etc. This is especially so for ultra high-resolution (8 MP and greater) image sensors and cameras. These effects can be calibrated to ensure there are no artifacts in the image. Adimec allows for this calibration in the camera to be done easily in the field to ensure compensation for all disturbances, including those due to system configurations or that may change over time, through Active Sensor Control (ASC).
ASC is an automated way to correct for various effects, such as fixed pattern noise (FPN), photo response non-uniformity (PRNU), shading, among others. FPN is seen as a pattern of ‘hot’ or bright and ‘cold’ or dark pixels within images taken under the same illumination conditions. PRNU is the variation of the output signal from pixel to pixel. ASC is about pixel-by-pixel correction and is not just an overall offset and gain adjustment.
Let’s explore this further…
An example of two pixel responses is shown in Figure 1. Assuming they both behave linearly, they show variation in offset (unexposed response) and gain (slope). The ‘black level’ is referred to as the average of the offsets of all pixels. A black level change in Figure 1 would be represented by shifting both graphs the same amount in (up or down) vertical direction.
Figure 1: Two uncorrected pixel responses
This type of offset is easily corrected on the camera before it leaves the factory. ASC goes beyond this and provides compensation to address issues in the image acquisition set-up process, such as non-uniformity of lighting source(s) and optics used in imaging chain.
We recommend you perform this for yourself to see the image quality improvements and what that can do for your system. Here is how.
Once you have implemented the Adimec camera into your system or test set-up, take an image in dark, and run the simple operation through a push of a button to complete the active sensor control operations. This can then be used immediately or written to the memory. The reading of the memory is done during the cameras start-up and requires no additional time.
Figure 2a: no ASC 16x gain Figure 2b: After ASC applied 16x gain
As a note, multiple sets can be calibrated in the field and stored in the non-volatile memory in the camera. This allows for optimized use for multiple lenses, for example, through a shift on the fly between each set during imaging for when other lenses are rotated in front of the camera.
And back to testing…if you want to further improve the image quality (pixel response), you can also run active sensor control on illuminated images. This allows for shading corrections among other things.