Choosing the correct industrial camera for your new and innovative system from the beginning can eliminate costly redesigns or upgrades in the future. The question is, how do you determine the best camera without being able to test it in the final design? Best is always subject to your needs but what are the exact needs for your company in order to beat the competition? There are hundreds of camera-options for just high-performance industrial cameras, so how do you begin your search?
In this three part blog series, we will suggest a step-by-step approach that will hopefully help in the camera selection process to find the best candidate. So to begin, here are some tips on how to identify the key camera parameters that are most important to you.
The best and most obvious place to start is at the end or in this case with the properties of the required resulting image. You can describe your image-needs in terms of:
These terms can be defined as:
Contrast is the difference in brightness between the light and dark areas. It may be negatively influenced due to reflections in the optics and or between reflections between sensor and optics. For precise measurements these reflections can be detrimental to accuracy. This relates to the dynamic range (ratio of the maximum output signal to the dark level) and linearity (the percentage deviation from the ideal response of an image sensor) of the camera. In some applications it might lead to the requirement to have the coverglass removed from the image sensor in the camera.
Resolution is the sensor resolution in combination with the field of view (FOV) that is being detected. It primarily defines the maximum spatial details that can be captured. The equipment you are building in combination with the measurement algorithm should give you numbers like pixels/object and objects per image.
Sharpness is affected by the combination of image sensor and optics. If both are not well matched, spatial details will be blurred.
Distortion is an ‘error’ in the spatial representation of the 2D scene within the image. The combination of image sensor and optics give rise to this artifact.
Noise can be shot noise at the sensor pixel level. At the image level view, noise is related to capability of the camera to represent a 2D scene with a certain uniformity. Non uniformity due to the camera is caused mainly by offset & gain differences (e.g. noise) between pixels, and by pixel-, row- and/or column defects. Extensive non-uniformity will limit the resolving capabilities of the camera, especially when image sensor resolutions increase (e.g. multi mega pixel field of views). When looking form image to image, it is the stability of the camera that is seen as noise. An unstable behavior will limit the ability to accurately capture subtle intensity variations between images. In other words, a badly designed camera can ruin the images from good image sensors.
After considering this how do you then determine what camera you need? You want all of these to be the best possible right? This would mean a camera with the highest values in many parameters such as those listed below:
- Intra scene Dynamic Range
- Detection Linearity
- Pixel (shot) noise
- Image Uniformity
- Optical Reflections
- Modulation Transfer Function (MTF)
- Resolution within the Field Of View
- Geometrical Distortion
- Camera Stability
- Frame Speed
You can identify the ideal values for all of the above, and then accept that a camera meeting all of those is likely not cost effective. It is therefore a good idea, to prioritize this list for the 5 most important parameters for you to achieve the image details you require. First you can likely narrow down the basics of resolution, and frame speed necessary. Then it can get a little harder. For example, determine whether your measurement is read noise or shot noise limited. You should also consider the system requirements, such as what kind of illumination you have to determine the actual sensitivity required or what optics will be implemented. If you buy a high-performance camera and then an insufficient lens or vice versus, you will not get the desired result. There is also which interface is preferred, especially if the project is an upgrade of an existing system.
Now you are ready to search for products that match your key specifications. All of the usual ways of internet research, trade show attendance, or phone calls to suppliers should give you a good indication of what your options are, but we will discuss this further in our next blog….