Day / Night Camera TutorialBy John Honovich, Published Jul 29, 2012, 12:00am EDT
Day / Night cameras are very popular but not often understood. In this tutorial, we explain what makes a 'true' day / night camera, break down the role of a mechanical cut filter, share a 5 minute demonstration video and compare day / night cameras to color only, electrical D/N, dual imager and IR cameras.
Mechanical Cut Filter
The key part of a day/night camera is the mechanical cut filter placed on top of the sensor. As the image below shows, it allows an IR filter to move back and forth.
When you want color images, the IR filter is moved in front of the sensor, blocking out Infrared Light. However, if it is dark out and you need more light, the IR filter is moved away from the sensor so that it can capture Infrared Light. Note: There is naturally infrared light in most environments, even if no IR illuminator is on (see our measuring IR report).
During the day, you want to exclude IR light because color images can degrade from IR exposure, such as the color shift and desaturation seen below:
However, at night, when visible light is poor, allowing IR light helps capture more details for black & white images.
Typically, the default for day/night cameras is to automatically switch from color to black & white mode when visible light is insufficient. Alternatively, you can force the camera to stay just in one of the two modes. This configuration menu (from Bosch) shows those standard options:
However, the terms used for day/night can vary and sometimes be confusing. Take Axis configuration options below. Instead of giving options for "color" and "monochrome" or "black / white" as is normally done, Axis's options are either IR cut filter "On" or "Off". While they are technically correct, it forces the admin to understand how cut filters work and deal with a double negative (i.e. 'cut' 'on'). If you put the IR cut filter "On", IR will be blocked and you will get color only; alternatively, turning the IR cut filter "Off" allows IR light to pass and show black and white.
Example of Color vs B/W Modes
When switching between the two modes, black & white absorbs more light (i.e., infrared light) that is blocked in color mode. This helps produce a better image while reducing the demand for more gain control (which drives visible noise). Our Lowering Light Levels test shows this. For example:
Even though the b/w image has half the amount of light, it is as detailed, if not more than the color image.
Advanced Options and In Action Video
The following video shows day/night cameras in action including 3 advanced options that are worth considering:
- Adjust the sensitivity for switching: Some people prefer to stay longer in color or black and white mode. You can use sensitivity level to accomplish this.
- Set a schedule for day/night: This forces the camera to stay in one mode, regardless of temporary lighting changes which can be beneficial if you expect short bursts of lighting changes. Note it may need to be adjusted every few months to account for differences in lighting from when the schedule was originally set.
- Impact of auto focusing: Cameras with auto focusing may allow an option to re-focus the camera when switching between day and night modes.
Make sure to watch the 5 minute video below:
Vs Color Only Cameras
Color only cameras, typically have a fixed IR cut filter. The upside is that they are typically ~$50 less than equivalent day/night cameras. However, low light performance is generally considerably worse. Indeed, because of the small price premium yet significant performance increase, many high end camera lines only offer day/night models with no color only versions. Anytime you buy a new camera, check whether it is day/night or color only.
Vs Electrical D/N
One confusing option is the 'electrical' Day / Night version. This is fake Day/Night as the IR cut filter remains fixed but the camera tries to compensate with image enhancement. It generally does not come close to the low light performance of a true day/night camera with a mechanical cut filter.
Vs Dual Imager Cameras
A few manufacturers offer models with essentially two cameras built inside - one is color and the other black and white, like so:
Performance is typically higher than a day/night model as both imagers can be optimized to, respectively, day and night operation. However, the performance increase is typically modest yet the cost is much higher as a second imager and lens is needed. Because of that, very few options exist in the marketplace. You can certainly find some (at a premium) and if you are not satisfied with Day/Night, dual imagers should be considered.
Vs Series Offering Color Only and B/W Only Versions
A few manufacturers (most notably Mobotix) offer the same cameras in color only and black & white only versions. The upside is that you optimize quality for day (or night) while minimizing cost compared to dual imager cameras. However, this forces the buyer to lose color or black & white. For instance, while such cameras might provide high quality night time video, no color is ever available even during the day. This is a tough choice for most buyers.
Vs IR Cameras
The next step up are cameras with integrated IR illuminators. Often these are true Day/Night cameras that add in IR LEDs to boost the amount of light available at night. See our D/N vs IR Camera tutorial for more.
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