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Multispectral

Mutispectral cameras acquire images from two or more spectral bands simultaneously.  The standard Bayer RGB color camera is, in this sense, a multispectral camera but is constrained iby the offsets between pixels of the three channels and by the relatively broad bandwidth of it s channels.  This is good for color imaging but generally not as good for data acquisition.  

The multispectral cameras we sell use Philips prisms for channel separation. This provides precise control over the channel bandwidths and premits the sensors to be aligned with each other with subpixel accuracy.  These cameras, made by Quest Innovations, are available in three and five channel models with a variety of spectral arrangements. 

Three-Channel Examples

Spectral Curves Description
rgb-curves.jpg R/G/B - This is a three-channel configuration in which the three bands are selected for color reproduction.  There is far less channel overlap in prism RGB cameras than in Beyer cameras but color reproduction is still quite good - this is the standard configuration for essentially all of the professional television broadcast cameras in the world.

 vnn-curves.jpg

Vis/NIR/NIR - This is a three-channel configuration in which one channel covers the visible band and the other two channels cover parts of the near-infrared band out to the silicon response cutoff.  The colors here just show the coverage of the bands.  As an option, the visible channel can be fitted with a Bayer sensor to provide five bands.

 ndvi-curves.jpg Trim Filters - The spectral band of any or all of the channels may be modified by the addition of trim filters. The example shown here is used in the agriculture industry to compute an index called NDVI used to assess plant health. 

 neut3-curves.jpg

Neutral Split - It is possible to have significant overlap in the bands, as in the case in many material and agricultural sorting and grading applications by using prisms that neutrally split the incoming radiation and fitting all channels with appropriate filters.  In this example, one channel provides a luminance measurement and the other two have specific detection bands.

 

Five-Channel Examples

 
 rgbnn-curves.jpg  R/G/B/NIR/NIR - This five- channel arrangement has identical sensors for separate full-resolution channerls for RGB color and for split-band near-infrared.  Not that the colors in the diagram only indicate the bands, not the color detected.  
 trim5-curves.jpg  Trim Filters - The spectral band of any or all of the five channels may be modified by the addition of trim filters. The example shown here is used in the agriculture industry for mearuring a set of parameters related to the health of plants as they grow in the fields.  The right filter set can show the need for water or fertilizer.
 neut5-curves.jpg  Neutral Split - It is possible to have significant overlap in the bands in a five-channel prism, as in the case in many material and agricultural sorting and grading applications by using prisms that neutrally split the incoming radiation and fitting all channels with appropriate filters.  In this example, one channel provides a luminance measurement and the other four have specific detection bands.

Because of the large variety of configurations possible in these cameras, it is not practical to offer them for sale online.  If you have an imaging requirement you think may be suitable for multispectral analysis, please send us an e-mail at sales@alt-vision.com and we will be happy to provide further information and pricing.

Additioan Technical Data

Philips prism white paper -  PDF here

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