Resolution vs Compression TestedBy John Honovich, Published Nov 24, 2014, 12:00am EST
They are not the same thing.
Unfortunately, too many industry people conflate them.
Worse, resolution and compression can silently undermine each other.
Compare the two images below. The resolution (aka pixel count) is exactly the same but the compression levels (and bandwidth) are much different:
Because of the compression difference, even though everything else is the same, the visual quality is much different.
Resolution vs Compression
Resolution, in surveillance, means the number of pixels (1MP, 2MP, 5MP, etc.) See: IPVM's Resolution Tutorial
Compression, in surveillance, means how much the pixels / video is compressed. There is a scale from minimum to maximum. In H.264, it is called quantization, ranging from 0 (least) to 51 (most). See: IPVM's Video Quality / Compression Tutorial.
All IP cameras compress video, typically in the middle of that scale. IPVM testing shows 28 is average though manufacturers vary somewhat. Moreover, manufacturers generally do not reveal the actual quantization level, displaying their own scale. To learn more, see: IP Camera Manufacturer Compression Comparison
Making Lower Resolution Look Like Higher Resolution
In this test, we took a series of 720p IP cameras, decreased the compression levels to see how far we had to go to make it 'look' like a 1080p camera with default compression levels. We then compared bandwidth consumption of each camera.
Making Higher Resolution Looks Like Lower Resolution
Also, in this test, we took a series of 5MP and 1080p cameras, increased their compression levels to see how far we had to go to make it 'look' like lower resolution cameras (1080p / 720p respectively) with default compression levels.
Our goal is to understand and show you:
- How much compression can impact visual quality?
- What benefits are there to reducing compression levels?
- What benefits are there to increasing compression levels?
- Can you get better quality or bandwidth consumption from such changes?
- Arecont 16 - 36
- If you are going to make adjustments on your camera's compression levels, understand what the model will allow or not, because manufacturers often limit this. Check using a video analysis tool or our results above.
- If you choose to do so, try a higher resolution camera with higher compression settings to save bandwidth with minimized quality reduction.
- Avoid taking a lower resolution camera and trying to decrease its compression level. Consider buying a higher resolution camera which may be better able to deliver that quality at comparative lower network / storage cost than decreasing compression levels.
Though H.264 allows compression / quantization levels of 0 to 51, most manufacturers restrict how little or much the user can compress.
We tested 7 manufacturers using a video analysis tool, with their low and high compression settings to determine what those constraints were:
Notice, only one allowed the full range.
Also interesting, Avigilon was the most restrictive, allowing the narrowest range of compression levels, especially blocking high compression levels.
Takeaway: How much you can improve quality (by decreasing compression) or decrease bandwidth (by increasing compression) will be impacted by what your choice of camera allows. Check that.
Lesson 2 - Higher Resolution Cameras Can Look Like Lower Resolution Ones and Save Bandwdith
This might be a 'hack' worth considering. If you take a higher resolution camera (say 1080p), increase its compression level (say to ~40), it will look similar to a 720p camera at default compression levels, like so:
The big benefit we found was that the 1080p / high compression video was, on average, 50 to 75% lower bandwidth than the 720p / default compression one.
We found this to be the case even in wide scenes with relatively low PPF, like so:
Again, bandwidth for the 1080p / high compression cameras was 50 to 75% less than the 720p / default compression one.
Testing a 5MP / high camera vs a 1080p default camera, the same pattern existed.
Lesson 3 - Higher Res / Higher Compression Tips
If you consider going the route of getting a higher resolution camera and setting it to a higher compression to get the effective quality of a lower resolution camera at a lower bit rate, make sure the higher resolution camera still has the same feature sets as the lower resolution ones.
In particular, verify that it has the low light, WDR and frame rates you require as some higher resolution cameras have comparative deficiencies there.
Lesson 4 - Lower Res / Lower Compression Bad Idea
Many people like the idea of lowering the compression level of a camera to get better quality. Our testing shows this is a bad idea, because of bandwidth spikes and difficulty in increasing quality.
In a high PPF / narrow FoV, our testing was able to get a 720p / low compression camera to 'look' like a 1080p default compression camera, like so:
However, to get there, the bandwidth consumption of the 720p / low compression was 200% to 400% greater than the 1080p / default compression cameras. As such, the penalty in trying to make it look better, both in network and storage costs, are significant.
It gets worse.
In a moderate PPF / wide FoV, our testing was unable to get a 720p / low compression camera to 'look' like a 1080p default compression camera, like so:
Despite being as aggressive with lowering compression on the 720p camera, it was still clearly visually inferior to the 1080p one.
And, even though video quality was still inferior, bandwidth ranged from 25% to 100% greater for the 720p / low compression camera compared to the 1080p / default one.
Keep in mind:
1 report cite this report:
Back to Top