When shopping for a security camera, most people look for resolution: either the Megapixel count (5 MP, 12 MP) or the catchy marketing term (4k Ultra HD, 1080p). People tend to think that bigger is always better. A 4k camera must be better than a 1080p camera, right? This is not necessarily the case.
Knowing how resolution affects your video security helps you shop smart. The size of the sensor can be as important as the resolution.
In this blog, we’re going to explain the relationship between resolution and sensor size. But first a little background.
How do digital cameras capture images?
The sensor of a digital camera is the equivalent of film in a film camera.
Light is let onto a sensor through a lens. The sensor receives and encodes the information, producing an image. Video is just a whole bunch of images presented sequentially so fast that our brains interpret it as the equivalent of movement in the real world.
We’re not going to get too deep into the technical details, but you need to know a bit.
Pixels and photosites
Image resolution is measured in pixels. Pixel stands for “picture element,” and means the smallest unit of a picture, that is, a single square of color. How does a camera determine what color a pixel should be?
A camera sensor is a sheet of prepared silicon of millions of photosites. A photosite is a light-sensitive cavity in this sheet of silicon. Each photosite produces a single pixel’s worth of information.
When light hits a photosite, electrons are energized. More light means more energy. A camera measures the changes in energy levels (voltage). The sensor sends this information along, and this information is what is used to produce an image.
In digital photography, an increase in light intensity increases the luminosity of a color, that is, how far on a scale between white and black a color is. An overexposed photosite produces pure white; an underexposed photosite produces pure black.
So that’s how we get shades. But who do we get color?
To produce a color image, manufacturers place a filter over the photosites. The filter blocks out certain wavelengths, allowing the camera to interpret what color light is hitting the sensor.
What does this have to do with resolution?
Resolution is the measure of how many pixels are in an image.
If an image measures 6,000 x 4,000 pixels, that comes to 24,000,000 pixels in total. The prefix Mega- just means million. So a 6,000 x 4,000 pixel image is a 24 Megapixel or 24 MP image.
You increase the number of pixels by increasing the number of photosites on a sensor.
Here’s where you can see how sensor size can be extremely important in determining the quality of an image.
To increase the number of pixels a sensor can produce, you need to either shrink or more tightly pack the photosites on a sensor. This can lead to less information gathered per photosite or energy bleeding from one photosite to its neighbors, causing inaccuracies.
Take that 24 MP image. If one sensor measures 0.5” wide and another sensor measures 0.75” wide, yet they both produce a 24 MP image, the first sensor needs to pack in photosites much more tightly than the second sensor.
In general, a more spacious arrangement of photosites leads to greater accuracy, improved low-light performance, and less noise. So a lower resolution on a larger sensor could improve your video picture quality.
And in the end, your surveillance video is all about accuracy.