In-Field Calibrations for Optimal Machine Vision Image Accuracy

Flat Field Correction (FFC) processing can be used to minimize or even remove artifacts to improve the image uniformity. The purpose of flat field correction is to ensure image uniformity regardless of exposure.

There are two components to FFC:

Local FFC – calibration done at the camera manufacturer to compensate for sensor imperfections
Global FFC – in-field calibrations to address issues in the image acquisition set-up process, such as non-uniformity of lighting source(s) and optics used in setup.

Local FFC

Local flat field correction can be done as a general offset for the whole image, or on a per pixel basis for better accuracy. For example in the Adimec QUARTZ series, we apply several corrections including the pixel based FFC while maintaining 4 Megapixels at 180 fps. Because this is done inside the camera, 12 bits rather than 10 bits are used for image processing for better accuracy.

Global FFC

Some machine vision cameras contain algorithms for in-field FFC through storage of multiple calibration setups so the camera can switch instantly during operation between different lighting-optics, optical filters and other setups.

We recently upgraded the QUARTZ series to allow for the storage of even more flat field correction sets (40 sets for 4 Megapixels). This feature is especially beneficial when the lenses or lighting is changed within measurements.

Figure 1. Image from a CMOS camera without Flat field correction

Figure 2. Image from a CMOS camera with Flat field correction

Other developments to the QUARTZ series are:

Improved frame-to-frame stability by a factor of 2.5 to correct for image sensor variations.
More Flat Field Correction sets to support True Accurate Imaging®
Reduced power consumption by about 2.5W for stable camera operation.
More efficient implementation of the dual CoaXPress interface
Support for higher resolution image sensors (e.g. 8 MP and greater)
More flexibility for customization options

As image sensors are becoming more power-hungry because of increased resolution, datarates, and therefore more complex blemish corrections, Adimec will continue to improve its camera platforms to deliver to the customer the high performance cameras they have come to expect from Adimec.

At the Vision International Trade Fair for Machine Vision in Stuttgart, Germany November 6-8, 2012, we will exhibit the upgraded QUARTZ series. In Booth number 1G68, we will demonstrate the Q-12A65, which is a 12 Megapixel camera with 66 fps over Camera Link using the latest CMOSIS CMV12000 sensor.

Advantages of in camera image processing: How camera technology makes a better picture