Q:Why IR Filter in Color Cameras necessary?
‧A:
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.
Article ID: 134, Created: July 14, 2009 at 1:42 PM, Modified: July 14, 2009 at 1:42 PM