Why IR CUT AHD Camera?
Different to human eyes, camera sensors can detect “near infrared” light-(wave near to un-visual light that just outside the range of the human eye can see). With such feature, the color reproduction is drastically affected. The plants in this view reflect more infrared than green light so they appear pink in daylight. An infrared-cut filter built in a IR CUT AHD Camera which only allows visible light to pass through, reflecting unwanted infrared. The image below shows the different.
IR Cut AHD camera with IR CUT or Without IR Cut performance :
Infrared cut-off filters, sometimes called IR filters or heat-absorbing filters, are designed to reflect or block mid-infrared wavelengths while passing visible light. They are often used in devices with bright incandescent light bulbs (such as slide and overhead projectors) to prevent unwanted heating. There are also filters which are used in solid state (CCD or CMOS) video cameras to block IR due to the high sensitivity of many camera sensors to near-infrared light. These filters typically have a blue hue to them as they also sometimes block some of the light from the longer red wavelengths.
In infrared photography, the film or image sensor used is sensitive to infrared light. The part of the spectrum used is referred to as near-infrared to distinguish it from far-infrared, which is the domain of thermal imaging. Wavelengthsused for photography range from about 700 nm to about 900 nm. Film is usually sensitive to visible light too, so an infrared-passing filter is used; this lets infrared (IR) light pass through to the camera, but blocks all or most of the visible light spectrum (the filter thus looks black or deep red). (“Infrared filter” may refer either to this type of filter or to one that blocks infrared but passes other wavelengths.)
When these filters are used together with infrared-sensitive film or sensors, “in-camera effects” can be obtained; false-color or black-and-white images with a dreamlike or sometimes lurid appearance known as the “Wood Effect,” an effect mainly caused by foliage (such as tree leaves and grass) strongly reflecting in the same way visible light is reflected from snow. There is a small contribution from chlorophyll fluorescence, but this is marginal and is not the real cause of the brightness seen in infrared photographs. The effect is named after the infrared photography pioneer Robert W. Wood, and not after the material wood, which does not strongly reflect infrared.
The other attributes of infrared photographs include very dark skies and penetration of atmospheric haze, caused by reduced Rayleigh scattering and Mie scattering, respectively, compared to visible light. The dark skies, in turn, result in less infrared light in shadows and dark reflections of those skies from water, and clouds will stand out strongly. These wavelengths also penetrate a few millimeters into skin and give a milky look to portraits, although eyes often look black.
Camera sensor get picture without filler
Photo source: https://en.wikipedia.org/wiki/File:Tree_example_IR.jpg
Camera sensor get picture with filler
Picture source: https://en.wikipedia.org/wiki/File:Tree_example_VIS.jpg
Read more about IR photography: