The increased field of view and/or throughput provided by 25 Megapixel Cameras can only be a real benefit for inspection and metrology applications with uniform images and linear pixel response. Active Sensor Control (ASC) is an automated way in a camera to correct for various deviating pixel conditions in an image sensor, such as fixed pattern noise (FPN), photo response non-uniformity (PRNU), shading, among others. With ultra high-resolution cameras, the impact of these effects can be even greater. For more background information on Active Sensor Control and how to test it in your system, please click the links to the previous blogs.
With optical measurement applications, the accuracy can depend on the reliability of the pixel information. ASC provides the most usable pixels in a VITA 25K image sensor based system. This is not simply just a factory process of mapping a pixel to be defective when it slightly misbehaves and remapping it with its nearest neighbors.
In a 25 Megapixel CMOS machine vision camera, there can be up to 10000 classical defect pixels. When the ASC feature is used in a system, we have seen a reduction of up to 10 times in real defect pixels. The goal is to make sure the metrology information in the image is preserved. Here we provide some system scenarios when this can be most beneficial.
There can be a lot of factors found in a system that influence the image performance. Here are some examples of common issues for when ASC can be of great help:
- Changing temperature: ASC can keep the image useable over a wider temperature range and with a short recalibration time.
- Different camera timing settings used: When you need to change the camera timing in your system, for example 2 ranges of integration times (or more) are used, two sets of calibration data (or more) can be stored in the RAM memory for switching to a different set with just a serial command, from frame to frame.
- Switching between multiple lenses: With multiple lenses, you need a uniform light level for your measurements. Once the desired light is set up, a calibration can be run for each lens. You can then run your measurements with alternating lenses and calibration sets. In machine vision this is known as a global Flat Field Calibration to compensate for lens and lighting effects. ASC has this feature integrated in the algorithm (it is only one small part) to get the best out of every image.
- Changing light/wavelength conditions: When light hits the sensor, it can behave differently for each wavelength. If this affects your image quality, ASC can be completed at the different conditions and then applied to get the best image.
- Better linearity required in brightfield: If the dark behavior of the camera is okay, but in brightfield use there is less linearity than you need for your measuring application, you can add a brightfield calibration through ASC for improved linearity.
More usable pixels enable the system performance enhancements desired from 25 Megapixel cameras. Active Sensor Control provides the most usable pixels, even under demanding system conditions.