Resolution vs Compression Tested

By: John Honovich, Published on Nov 24, 2014

They are not the same thing.

Unfortunately, too many industry people conflate them.

Worse, resolution and compression can silently undermine each other.

The Impact

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

Compression Defaults

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.

Why

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?
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Comments (20)

...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.

Higher than what? Than other cameras I have? Other cameras I could buy?

Lower than what?

Roger, as explained in the examples throughout the test report.

his assumption.

 

we dont think about YOU and your property incessantly.

 

...... and you'll be fine  ;)

John, this report is very beneficial to better understand the relationship between resolution and compression settings and the impact upon a users perceived impression of picture quality and standards. However, the image samples generally relate to static targets. If you have a moving target and considerable scene change would there not be an increased risk of more compression artefacts at higher resolution with higher compression? Which would you expect to look better and have sharper stills, a 6 IPS recording at 720p resolution at 2Mbps CBR or a 6 IPS recording at 1080p resolution at 2Mbps CBR assuming it was a Hikvision or Dahua camera at the highest quality setting?

"Which would you expect to look better and have sharper stills, a 6 IPS recording at 720p resolution at 2Mbps CBR or a 6 IPS recording at 1080p resolution at 2Mbps CBR assuming it was a Hikvision or Dahua camera at the highest quality setting?"

If you are using CBR, you can not control the quality settings, by definition. The camera will do that automatically (i.e, as it hits / exceeds the bandwidth ceiling, it will increase the compression level to maintain the bit rate requirement).

As for 720p vs 1080p, I would expect the 1080p to deliver more details than the 720p, even if it had moderately more compression than the 720p in your 2Mb/s fixed bitrate scenario (i.e., the increased pixels would more than offset the moderately higher compression).

Your scenario would need an even, well lit scene to be true John. In low lit areas, a typical Dahua or HikVision camera will well surpass the 2Mbps mark natively and would then become heavily compressed. From the article above, it seems like the 720p would suffer far less than the 1080p.

So I think the real question become where is the trade off from higher res/higher comp to lower res/lower comp a net zero vs a bias one way or the other. I would assume this is a very subjective test and also model/firmware specific.

We'll run a test of 720p vs 1080p in low light this morning.

Please don't speculate. If you think something should be tested, either ask us to test it or submit your own test results.

Btw, we tested 7 models and the patterns were clear across the models, so your assumption that this is 'very subjective' and 'model/firmware specific' will need more evidence to back it up.

John,

We both have speculated here to a degree. My usage of Dahua and Hik cams have shown me that, generally speaking, it is hard to keep them anywhere near 2Mbps in darker scenes, IR or not. It's not to say it isn't possible to turn down sharpness and change other settings to keep the bitrate as low as you can, but under 2Mbps is a stretch. So, as per your testing has shown above, if you have a lower compressed 720p image vs a higher compressed 1080p image, the 720p may win out. However, you suggested the 1080p camera would provide more detail in your reply to Andrew above, which seems to cut against your own findings. So you can see the source of my confusion.

As far as the subjective comment, I was referring to the judgement we all have to make about which image looks better. We can measure many things, such as resolution, compression, etc., but I don't know of a quantitative factor for image quality. I think we would all most likely agree on our picks of favored images, but that just means we are being equally subjective.

"So, as per your testing has shown above, if you have a lower compressed 720p image vs a higher compressed 1080p image, the 720p may win out."

Please stop speculating. We are literally testing this right now. We'll post the results when finished.

"In low lit areas, a typical Dahua or HikVision camera will well surpass the 2Mbps mark natively"

As a point of reference, the typical Dahua or Hikvision camera has integrated IR. More than 60% of both Dahua and Hikvision models have integrated IR, verified by the 400+ models we track in the IP Camera Finder.

So we will test a Dahua and Hikvision IR camera here.

Looking forward to the results of the tests. Ideally would appreciate tests being also performed with good lighting conditions and with high scene change. System designers are always asking me what bit rate they should set a camera at relative to resolution and recording frame rate to achieve high quality play back without compression artefacts. It would be great to establish some guidelines to follow for popular cameras such as Dahua and Hikvision.

"System designers are always asking me what bit rate they should set a camera at relative to resolution and recording frame rate to achieve high quality play back without compression artefacts."

They should not set bitrates (i.e. CBR). Use VBR to ensure that you do not get compression artifacts.

We have done many bandwidth tests (each camera tests comes with bandwidth stats at the bottom). The level of bandwidth depends on the camera model and the scene.

The findings of this test is about patterns, not specific bandwidth levels for individual models. The same thing for a test like Testing Bandwidth vs Low Light (e.g., this shows that when lights go down, bandwidth goes up significantly, but the absolute amounts will vary).

John, most of the projects we get involved with for end users and integrators require continuous recording with a guaranteed recording duration. Dahua hardware is typically deployed at VBR with a capped bit rate setting and the highest quality setting (= 6), typically an IP-HDBW3202 camera may be configured at 6 IPS, 720p resolution, VBR capped at 1,920Kbps highest quality setting (= 6) or at 6 IPS, 1080p resolution, VBR capped at 3840Kbps highest quality setting (= 6). This method allows us to guarantee a minimum recording period as we can calculate the worst case storage requirements and our field testing suggests at these settings we hold picture quality and don't get compression artefacts. However, knowing the "sweet spot" per camera model for encoding settings for holding picture quality with complex changing scenes and guaranteeing recording duration and bandwidth usage is very valuable and any further advice is much appreciated. Dahua claim their newer Eco Savy series such as the IPC-HDBW5202 is more efficient with compression and can provide savings with bandwidth and storage. Have you or can you do comparisons between these different series cameras to confirm if their claims are correct or not without sacrificing picture quality?

We did some additional testing with integrated IR cameras this morning, on this topic, and as well as our Bandwidth vs. Low Light test which we've updated and added to our Bandwidth Guide.

In answer to specifics regarding Dahua and Hikvision 720p/1080p in low light:

  • 1080p does not have a major advantage over 720p in low light, even uncapped. See this example below. Details are only very very slightly improved in the 1080p stream. Quantization on both of these streams was ~29 in Hikvision and ~24 in Dahua (for some reason Dahua quality "4" didn't result in Q28 as it normally has in other models, so it was a bit lower than Hikvision).

  • With a 2Mb/s VBR cap, the same is true. Quantization is higher in the 1080p stream than 720p (Q35 vs. Q33 in Hikvision, Q30 vs. Q29 in Dahua), details delivered are still only marginally different.

Ethan,

Thanks for taking time to test this out. That said, I do have a few questions if you don't mind me asking.

1) The uncapped cameras you used were which models?

2) Did you happen to note the bandwidth usage for the uncapped tests?

3) When you said the quantization increased from 29 to 30 for the Dahua cams, was that true for both 720p and 1080p? They both had the same quantization with the 2mbps cap?

Again, great work. It's much appreciated by members such as myself.

Sorry to dig this from the grave, but I was still hoping for a response from Ethan above.

John,

I don't think Benros has enough pixels between his eyes there, I would not be doing my job if I did not tell you :)

Look familar?

Hi John,

do you have a camera with controllable preprocessor (noise reduction step)? so, is it possible to play trade-off between compression and noise reduction, keeping the same visual quality or same bitate and monitoring bitrate or quality change?

my understanding of your results with resolution / compression / bitrate is that low resolution with low compression ratio can't provide better visual quality as it effectively wasting bitrate to encode noise. and hi-res/hi-compression has a side effect of aggressive noise reduction.

or we can turn this inside out - instead of reducing noise algorithmically it is possible to reduce (lab-only, not in real life) noise physically, by providing more light. is it possible to test, how this hi-res/hi-compression vs lo-res/lo-compression will behave if you increase illumination 2 or 4 times?

can you take a try with that?

"do you have a camera with controllable preprocessor (noise reduction step)?"

Do you mean a camera that allows us to adjust the DNR setting? e.g., see: Camera DNR (Digital Noise Reduction) Guide

yes, exactly that. thank you for that link - this is what i was asking for!

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