If you want to make sure the right color pills are in a blister pack, the right color wires are where they should be or that food, plastic parts or other items are properly sorted and classified by color, you need a machine vision system with a color camera. But what type of camera best suits your application? There is a wide range of machine vision cameras available with Bayer color filters that give you high-quality images for basic color applications. But for many applications, Bayer cameras may not be enough. Instead, you may need the color fidelity and spatial precision offered by three sensor prism-based cameras.
To understand if your application requires a three sensor prism-based camera, this blog explains some of the differences between a standard Bayer camera and a high-performance 3CCD or 3CMOS color camera.
Bayer cameras rely on a predefined pattern of color filters which overlay the pixels on the camera’s imager. Calculating the RGB color for any specific pixel requires a process of interpolation which looks at surrounding pixels to estimate the values for the two colors not captured by that pixel’s filter. Unfortunately, this results in an averaging of color values, making it difficult to distinguish subtle shading differences. At the same time, the considerable overlap in spectral response between red, green and blue filters creates even greater uncertainty for some color families, leading to an overall muddiness of the color image.
3-sensor color cameras, however, utilize high-quality prisms with dichroic filter coatings to split incoming light into three separate imagers based on spectral wavelengths. The three precisely aligned sensors provide a separate red, green and blue intensity value for each pixel in the image with no interpolation required. The result: a more precise set of values enabling subtle color differences to be more easily detected and measured.
Furthermore, the hard dichroic coatings on the prism have steep spectral response curves; they minimize color crosstalk to produce more vivid color across the full spectral range. As an added benefit, the dichroic prism filters have higher light transmittance than Bayer filters, giving 3-sensor cameras a sensitivity that is typically greater than comparable Bayer cameras. Another key difference is the level of spatial precision. In Bayer cameras the level of spatial precision is much lower since the Bayer camera averages three by three sections of the imager to create the final image.
Need help selecting the right color camera for your application?
Download our Tech Guide: Color Imaging, and walk through the steps of selecting the right color imaging camera for your application.
The process of Bayer color cameras essentially reduces a cameras spatial resolution by a factor of three or more. This results in a lack of sharpness that makes it impossible to see or measure small details in an image. For example, when using a 1.4-megapixel Bayer camera with a field of view set to capture a complete box or package, small printing or barcodes become unreadable due to interpolation. When you use a a 1.4-megapixel three-sensor camera for the same setup, not only are the colors more accurately preserved, so is the level of detail, providing much greater flexibility for applications needing color inspection as well as barcode verification, OCR or accurate edge location and measurement.
You could consider opting for a Bayer camera with significantly more resolution to try to solve this problem. However, higher resolution typically means higher costs, a slower frame rate, slower image processing, and more expensive optics – and it still wouldn’t solve the color averaging and crosstalk issues. With a 3-sensor prism camera, resolution can be kept at a minimum to preserve frame rate and reduce image processing overhead.
The right choice for your vision system depends on on how demanding are the color requirements of the intended application. The more critical the color requirements, the more important it is to weigh the differences between a Bayer camera and a 3-sensor prism camera.
Need help selecting the right color imaging camera for your application? Read our Tech Guide: Color Imaging, and walk through several steps to select the right color imaging camera for your application.