Resolution is important in video surveillance. This article series discusses security camera image resolution – what it is, why it’s trending upwards and how to choose the best IP camera resolution
Resolution is important in video surveillance. The resolution of an IP camera determines how well video can be captured and seen. This article series discusses security camera image resolution – what it is, why it’s trending upwards and how to choose the best IP camera resolution.
Due to the importance of camera resolution, a basic understanding is warranted.
According to Theia, resolution can be understood from the following points: it can be expressed as the number of pixel rows or columns on the sensor used to record an image (for example 1,600 x 1,200); it can be expressed as the total number of pixels (1,600 x 1,200, for example, equals a total of 1,920,000 pixels or 2-megapixel); it can be the level of detail with which an image can be reproduced or recorded; and it can be specified in pixels per foot or meter at the object.
Common IP camera resolutions
So what are some of the common, mainstream security camera resolutions in the market? Right now,
2MP IP cameras are still mostly used due to their price and performance.
“In terms of volume, the 2MP solutions still dominate the market. However we do see a breakeven between 2 and 5MP designs expected in 2022,” said Hartmut Sprave, CTO of MOBOTIX. “Also with regard to the often used cloud solutions, the 2MP resolutions are the more cost-effective solution. In addition, they are still absolutely sufficient for many applications. Especially in the low light area, the lower resolutions are currently even better due to larger pixel-sizes collecting more light.”
“The shift has been to move from older 4:3 aspect ratios, such as those found in 4MP and 5MP cameras, to 16:9 versions of 4MP and 6MP. Many 4K cameras started out at 12MP in a 4:3 aspect ratio, and they have moved to 8MP in a 16:9 aspect ratio,” said Aaron Saks, Senior Technical Marketing and Training Manager at Hanwha Techwin. “That being said, 2MP full HD is still popular and in high demand due to the nature of surveillance being 24x7 and the desire to reduce bandwidth and storage."
Yet, demand for
higher resolution is increasing as users require more details and more areas of coverage.
“Although the 2MP has been the de facto standard for the industry, it is now trending towards 4MP and 5MP. This is driven by improved compression algorithms and the desire for security footage that provides a greater level of detail. PTZ cameras typically have long optical zoom capability, thereby requiring less resolution to get the necessary pixels on target,” said Kambiz Asrar Haghighi, Director of Product Management for Video Security & Access Control at Motorola Solutions.
Choosing the right resolution, then, still depends on the user’s own requirements. “2MP cameras were once a mainstream of the market. In today’s world, 2MP, 4MP, 5MP and 4K are the most common resolutions used. But their applications will depend on the use. A 2MP camera might be most appropriate for a hallway whereas a 4MP/5MP might be required to cover an area with a wider field of view such as a cafeteria or a parking lot,” said Tim Loth, Sales Engineer Team Lead at i-PRO Americas.
We’ll further explore high-resolution IP cameras and their uses in a second article.
The importance of lens in resolution
The image sensor and lens of a camera are closely tied to resolution. This is particularly so for the lens. It’s important to note that the higher the resolution, the more a high-quality lens is needed to accommodate that resolution.
“The lens must be matched to the image sensor. If you were to use a lens from a few years ago on a 4K camera, the quality and grain of the lens would limit the detail that the camera would be able to output. There are many factors that go into making a high-quality lens, including the number and design of the lens elements, their material (glass vs. plastic), and more. Many lenses are now rated to 4K resolution,” Saks said.
And there have been improvements made to lenses and sensors to make the camera perform better. “In the industry, examples of recent innovations include: RGB-IR sensors that do not require cut filters for IR operation, and square sensors instead of 4:3 or 16:9 that enables better vertical field of view (VFOV) for the intercom and fisheye applications,” Haghighi said.
“There are permanent improvements in the field of image sensors, which then consequently require improvements in the lenses, because the performance of the lens must correspond to the performance of the image sensor in order to guarantee the best image quality offered,” Sprave said. “A characteristic feature for the quality of a lens is, for example, the lens edge blur/shading. The MTF (modular transfer function) is also extremely important – we are talking about delivering constant optical resolution across the full lens glass surface. It describes the optimal matching of resolution and contrast to each other. At MOBOTIX, no camera leaves production without the edge blur and MTF being checked and found to be optimally adjusted.”
Lens selection
Given the importance of lenses in IP camera resolution, selecting one is critical. One way is to calculate the Nyquist frequency.
“The Nyquist frequency is considered the quality standard for a well resolved image. The Nyquist frequency, and related Line Pair per Millimeter (LP/MM) specification, provide the resolution properties of a lens and can be used to help select the correct lens for your camera. LP/MM determines the smallest width of a pair of adjacent pixels that can be resolved by the lens,” said Jeff Gohman, Co-Founder, President and Chief Optical Designer at Theia. “To calculate the Nyquist frequency first find the size of the camera sensor’s pixels. An example sensor is the Sony IMX226, a 12 megapixel sensor which has a 1.85µm pixel. Next you convert the pixel size from µm to mm (= .00185mm), multiply that by 2 to get line pairs (= .0037mm) then take the inverse (1/.0037), which equals 270 line pairs/mm. Now check the resolution of the lens to see if it is rated at 270 lp/mm or better.
He further mentions the importance of using a lens calculator, whereby the user enters the resolution and sensor size plus other details about the camera, and the calculator indicates the right lens for the application. Lens calculators can be found on asmag.com’s
camera calculator page.
The type of lens is also important. It’s essential that users consider their own use cases and requirements before selecting a lens that fits their camera solution.
“There are fixed lenses and zoom lenses. Fixed lenses are one size and cannot be changed. Zoom lenses have variable sizes, allowing you to adjust the field of view for any application. To get an optimal image for a specific resolution, it’s important to evaluate the required field of view, listen to the customer's needs and then decide on the resolution and type of lens,” Loth said.