Camera Resolution Overview

Resolution terms may be used to describe the size of the image captured at the camera, transmitted over a wire, displayed on the screen, or recorded on the hard drive. CIF, QCIF, 2CIF, 4CIF, and Megapixel are common terms for resolution.

When comparing megapixel camera specifications you may notice pixel counts slightly different from the above. This is because some cameras will specify the total number of pixels captured by the sensor, and others will specify the ‘effective’ pixels. Some of the total pixels are used to contain technical housekeeping type of data, and are not contributing towards the ‘effective’ details of the image.

Those of you familiar with CCTV know that the resolution of an analog camera is typically listed as “TV lines”. These “lines” refer to the horizontal resolution of the image; therefore a 700 line camera has better resolution than a 420 line camera. NVRs and DVRs that are ‘Full D1’ can record all the detail captured by the highest resolution analog cameras.

One of the most common questions we get is “What resolution camera should I buy?” Of course, it depends. Each camera in your application may require a different resolution. It comes down to how much detail you want, what platform (if any) you already have in place, and how much is your budget. Examples of applications where you can easily justify spending more for higher resolution are recording monetary transactions, desiring facial recognition, or reading license plates.

It is important to consider what platform your camera will be running on as that may limit your resolution options. To summarize CCTV platforms: Analog cameras transmit over coax and can capture up to 700 lines (approximately full D1). HD-SDI cameras capture higher resolution images then encode / decode the data to run over coax. IP or network cameras transmit over CAT5 (just like computers). You can run analog cameras on a CAT5 network, or IP megapixel cameras over coax, but it would require additional hardware and added complexity so it’s not recommended.

It is important to keep in mind that the higher the resolution of the cameras, the more bandwidth and hard drive space you will need to transfer and store it.

It’s useful to know that the human eye is more sensitive to horizontal resolution than vertical resolution. So for example, to the human eye, there is not much perceived difference between 2CIF and 4CIF. The other issue to know about the human eye has to do with frame rate. In CCTV the maximum frame rate available per device is typically 30fps and that is considered ‘real time’. Above 15 fps is going to look pretty good but may not be useful for a conviction in a court of law. Some devices will list different resolutions at different frame rates. So for example, an IP-camera might document its resolution as “3MP at 20fps” or “2MP at 30fps.”

In a CCTV application you will have many cameras with different resolutions but usually only one recording device. So make sure that the recording equipment you choose has at least the resolution capability of your highest resolution camera. Also, make sure it has enough hard drive space to record all of your cameras for a reasonable period of time given your application. Image resolution is most crucial when something happens and you need to playback that video. If you need to zoom in on a piece of video, the quality of that zoomed in image depends on the recorded resolution. So configure each channel of the DVR separately to record at the highest resolution that matches the camera.

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