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Industrial Cameras and Vision Systems 
 

A Quick Look At The Difference an IR Filter Makes to Image Colour

 

Have you ever wondered what difference an IR filter makes to the image?

Most modern industrial cameras have IR filters placed between the sensor and the lens mount (IR filters can also be found in some lenses). This is due to the fact that modern CMOS sensors are more sensitive to IR and for most applications IR is not needed. Therefore the filter is used to block unwanted IR from reaching the sensor. In theory this is great but what visible difference does the IR filter actually make to the image? Why is IR unwanted and what happens if the filter is removed?

Below are two images taken with the same camera (DFK 72BUC02) and lens (M0814-MP2) of an identical scene. The image on the left was taken with the IR filter removed from the camera while the image on the right is taken with the IR filter in the camera.

   
 Without IR Filter  With IR Filter

As you can see the colour difference of the shirt between the two images is very noticeable. With the IR filter the correct colour (black) is captured whereas without the filter the shirt appears to be a brown colour. This is caused by the IR hitting the sensor. This is not good if a colour accurate image is needed.
Interestingly the rest of the image seems unaffected by the filter. This is most likely due to IR reflecting properties of the shirt fabric.

I hope this quick experiment has been helpful in showing the difference an IR filter makes and why they are needed in cameras.