Purpose of IR Filter in Color Cameras
An IR filter – or IR cut filter - is a color filter
blocking the infrared light. There are several good reasons for using an IR-cut
filter. Using a color camera to achieve realistic colors in white light
requires an IR-cut filter. The color spectrum seen by the human eye is quite
limited compared to the spectrum seen by a CCD camera. Especially, in the near
infrared region of the spectrum the difference in sensitivity is significant.
This is important to know since many light sources, including the sun, emit
infrared light. A CCD color camera in daylight without an IR-cut filter will
therefore see a significant amount of infrared light resulting in strange
colors. Another reason for using an IR-cut filter is the limited color
correction for many lenses. It is difficult to design imaging optics covering
both the visible spectrum and the near infrared spectrum at the same time.
Therefore, many lenses have different depth of focus for the visible and the
infrared spectrum. Anyway, the IR-cut filter cuts away a significant amount of
the overall collected light and thereby affects the sensitivity in a negative
way. In general, color cameras are one factor less sensitive compared to
monochrome (depending on the CCD chip). This is primarily due to the IR-cut
filter.
Info courtesy of Jai
Camera Solutions