Understanding IR-Cut Filters: How Can They Empower Day/Night Embedded Vision Applications?

day night cameras

This article talks about IR Cut Filters and how they impact camera solutions focusing on day/night camera applications.

Camera detector technologies such as CMOS, and CCD are excellent at capturing accurate color pictures in daylight. The problem is that the camera sensors can detect near-infrared light, which the human eye cannot. This is necessary for night vision recording, but it distorts the colors of recorded images during the day. An IR-cut filter is a solution.

IR-cut filters are used in day-night cameras. They function by filtering out undesired infrared radiation, preventing it from altering daylight image colors and making them appear more realistic. When the camera is in night mode, the IR-cut filter is turned off, allowing the camera’s light sensitivity to drop to very low lux levels.

What is an Infrared-cut Filter?

To create realistic color images, color CCD or CMOS cameras use infrared (IR) cut-off filters. IR filters can efficiently block visible light, allowing only the red portion of the light spectrum to pass through.

Infrared filters can transfer around 700nm to 900nm within certain visible light spectrum’s “near infrared” band, which ranges from 700nm to 2500nm. When employing such filters, you could change a tree’s green foliage to white or darken the sky above, just like you would if you were using an old film, to create unique photographs.

This can be accomplished using either absorption or reflection optical techniques. A unique type of optical glass is used to create absorption filters because it can absorb near-infrared light. Infrared light is efficiently reflected using reflection-type filters, which are short-pass interference filters. Typically, CMOS cameras employ reflecting IR filters, while CCD cameras utilize adsorbing filters.

Working of IR-cut Filters

The multi-layer coatings on the filter’s surface are primarily responsible for the filter’s effect.

Filters are pieces of glass that are connected to the front of a lens and by which all incoming light must pass through. The use of optical glass which is completely clear and colorless is followed by the bonding of a coating with unique chemicals to this filter to block UV and IR light rays outside of the specified range of the lens’s front. This filter is not appropriate for wide-angle lenses since the transmission factor is dependent on the light incidence angle due to the dense over-layer. With ordinary and telephoto lenses, it is suitable for astrophotography. Other filters are colored or provide unique effects, including light “starbursts.” Yet, the infrared filter is the most important type of filter for IR photography.

Infrared filters come in two varieties: those that pass visible light while passing IR light and those that pass visible light while passing both types of light. Digital video and still cameras with CCD or CMOS sensors frequently employ IR-blocking filters to stop stray IR light from penetrating the sensor’s sensitive near-infrared region.

Devices with powerful incandescent bulbs can utilize an IR-cut filter to stop accidental heating.

Considerations while employing IR-cut filters

When it comes to creating a high-quality day/night cameras that can be expected to give the best-captured photographs with little color distortion, accuracy and control are of essential importance. The adoption of an IR-cut filter can enhance both with the sharpest changes between the transmitting and reflecting bands.

Coating selection

The usage of coating and the superiority of the substrate make IR-cut filters distinguish themselves from others. According to the studies, the best solution is an anti-reflective hot mirror coating on a high-quality borosilicate substrate. Coating to the back surface significantly increases light transmission.

Substrate selection

When used as a substrate, borosilicate has great chemical resistance to alkaline and acidic solutions and does not deteriorate normally. The optical component it is utilized in can withstand drastic temperature changes while still preserving structural integrity because of its low thermal expansion. In comparison to other materials that are prone to cracking or breaking in harsh environmental conditions, borosilicate actually does stand out.

The benefits of IR cut-filter:

Color distortion

IR-cut filters are useful for day-and-night cameras. IR light, in general, causes color distortion throughout the day. They perform by blocking unnecessary IR light to keep it from affecting the colors of daytime images, making them appear much more realistic. The filter moves away from the way in order for the IR light may reach the picture sensor when the light level drops below a specific threshold. Additionally, in order to maximize the effectiveness of the IR light, the camera switches to black-and-white mode. The IR-cut filter turns off while the camera is in night mode, allowing the camera’s light sensitivity to drop to extremely low lux levels.

Realistic colors

Realistic colors in white light may be produced with an IR-cut filter on a color camera. Once compared to the spectrum captured by a CCD camera, the color range of the human eye is generally somewhat constrained. The near-IR region of the spectrum is where the difference in sensitivity is still the most obvious. If an IR-cut filter is not used, a significant amount of infrared light will come through, producing unexpected hues.

Color correction in lenses

Developing imaging optics that cover both the visible and near-IR spectrums is frequently difficult. Because of this, many lenses in the visible and infrared spectrums have different depths of focus. In these situations, the IR-cut filter filters out a substantial percentage of the received light, enabling lens color correction.

IR-cut filter-dependent embedded vision applications

The article concludes with a discussion of a few embedded vision applications that apply an IR-cut filter:

Smart Security Cameras

Most surveillance cameras are meant for day/night camera operations and comes with infrared lighting. The IR-cut filter is installed in front of cameras equipped with a night vision sensor. The IR illumination light is invisible to the human eye; however, the camera sensor could see it accurately. If the image quality is good in monochrome mode, the IR radiation has a significant impact on the image during the day. Additionally, smart security cameras with night vision have an IR cut filter to block light and produce an accurate image.

Automatic Number Plate Recognition (ANPR)

Based on a photo taken by an ANPR camera, an ANPR system should be able to recognize a vehicle’s license plate number with accuracy. These solutions demand day/night camera solutions. Combinations of procedures such as real image capture, character location and identification on the plate, and optical character recognition can be used to accomplish the task. A color camera with an IR-cut filter may capture sharp images at night. As a result, it aids in identifying the specific symbol image, the number of characters, and the text brightness level on the license plate.

Summing Up

When transitioning from day to night mode, IR-corrected optics avoid any out-of-focus photographs. These lenses always focus the incoming light onto the same pixel and automatically correct the changing refraction of various wavelengths. Standard lenses provide comparable daytime image quality to IR-corrected lenses. The advantages of an IR filter can influence your decision to employ one in any centralized way.

I feel this post provides a better understanding of how an IR-cut filter performs. If you have any questions or are interested in including embedded cameras in your products,

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