Resolution: 4K vs 2160p vs 8.3MP

Author: John Honovich, Published on Apr 24, 2015

4K, 2160p and 8.3MP all basically refer to the same 'thing', just different dimensions of it.

While total pixel count has historically been the most common technique (e.g., 1MP, 2MP, 3MP, 5MP, etc.), naming by vertical count (e.g., 720p and 1080p) have become more common in the past few years.

Now, naming by horizontal count / lines (e.g., 2K, 4K, etc.) is a growing trend.

In this note, we contrast the pros and cons of each element and how to best use them in designing surveillance systems.

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Comments (22)

I was always under the belief the "p" was also an indication of Progressive Scanning as opposed to the "i" of Interlaced Scanning? While seeing Interlaced video feeds has moved into a thing of the past so I can understand it not being mentioned does the "p" not still indicate Progressive?

Thanks Zeb. The number next to the P indicates rows / vertical count.

As you allude to the p vs i difference is no longer a material concern since everything is basically progressive now but the origin of the letter 'p' in this context is from progressive.

I've updated the post to note this.

The p is suggestive of the scanning method, progressive, and an i indicates interlaced.

When it's a p, it also refers to the number of horizontal lines to be scanned, or the vertical resolution. When it's an i, it refers to the number of fields, where 2 fields = 1 line. You therefore cut the number in half to get the vertical resolution in lines. Having said that, you are unlikely to run across an i in a camera sensor specification, since they are all pretty much progressive these days.

FWIW, the p I feel is the most descriptive because it implies a 9x16 aspect ratio. If you see 1080p, 720p or 2160p, you also know the horizontal component and therefore also the MP. On the other hand this also limits its use to primarily those aspect ratios.

"FWIW, the p I feel is the most descriptive because it implies a 9x16 aspect ratio."

Counter - 480p. From Wikipedia:

"480p is the shorthand name for a family of video display resolutions. The p stands for progressive scan, i.e. non-interlaced. The 480 denotes a vertical resolution of 480 pixel high vertically scanning lines, usually with a horizontal resolution of 640 pixels and 4:3 aspect ratio"

Yes, you are correct about 480p and other TV formats, though when it comes to sensors they are as about as rare as interlaced ones, because NTSC allows the more common 720x480.

The larger point remains though, since it implies as you indicate, a corresponding horizontal resolution.

Whereas with 7K we have no idea what the vertical is and with 6 MP we can't be sure of either. Though both are of course far better understood than the upcoming Samsung 5 MB specification. ;)

All you need to know is 7k is better than 4k and next year a lot of 8k televisions are being released from what I saw at CES. Some days I miss my Packard Bell Color television with 13 channels and a real "clicker"

Some days I miss my Packard Bell Color television with 13 channels...

I had a 19" Color RCA, cheap though, no Channel 1. ;)

@Greg ... that's funny! When I was a kid, I WAS the clicker!

Yeah, my Channel 1 (or maybe Channel 0) went to the UHF selector. Man, that was a long time ago.

I believe you have incorrectly swapped the terms "columns" and "rows" in the MP paragraph above...confuses the explanation. Helpful article though.

Hey Brian, thanks for catching that. It's been fixed.

In my humble opinion, I believe the terms like 720p, 1080p, 4k, etc. should be used when in line with HD standards, as they span across multiple industries. When outside of that, MP works just fine. It is incumbant upon all of us, though, to remember that when MP is used, then it is absolutely important to know the specific format. For instance, 2mp traditionally has been 1600x1200, but I've also heard it used for 1080p (technically 2.1mp) and we all know that the image clarity between these two resolutions are not the same.

"For instance, 2mp traditionally has been 1600x1200, but I've also heard it used for 1080p (technically 2.1mp) and we all know that the image clarity between these two resolutions are not the same."

What do you mean by image clarity here?

1600 x 1200 is a different aspect ratio than 1920 x 1080 but I am not sure I would say one has better or worse 'image quality' than the other.

Assuming the FoV width is the same, 1080p cameras typically provide clearer images based on my experience....closer to 3mp 4x3 cameras, but without the extra height.

I suspect you might be seeing that because most 1600 x 1200 cameras are older ones, using older sensors, that might not have true WDR, etc.

That might explain the different in image clarity, but that's not directly a result of the pixel count / resolution.

Assuming the FoV width is the same, [1920x]1080p cameras typically provide clearer images [than 1600x1200].

Technically that's true of course, because your horizontal PPF would increase by 20%. 1920/1600.

But how would the FOV width stay the same? Assuming the focal length and sensor's pixel size is constant, your FOV would be wider by 20% and then the PPF would end up being the same, no?

Obviously, this isn't an all-inclusive statement, and I guess I had assumed that everyone would know that. More often than not, I see the FoV determined more by width than height. If using VF lenses and you need a 20ft wide FoV, you'll get more pixels per foot using a 1080p camera than a 1600x1200 camera...that's basic math. That said, there are numerous variations causing this to change, like corridors, where this would not necessarily apply, but that's not as common as the traditional example I used.

The point of my original post wasn't to push an all-encompassing view generically applied to all applications -- we're all beyond that. But to the uneducated end-users, using 2mp as a description for both 1080p and 1600x1200 does cause confusion because despite the difference between only 153,600 pixels (exactly half the pixel count of a VGA image), the effective pixel density (ppsf) will be higher with 1080p cameras compared to 1600x1200 2mp.

Sorry to cause such a ruckus, everyone.

"the effective pixel density (ppsf) will be higher with 1080p cameras compared to 1600x1200 2mp."

But the total area captured / monitored will be less, assuming the same FoV width, because the 1600 x 1200 will have a taller FoV.

I don't think this is a huge issue but I am worried about leaving statements that imply one resolution inherently provides 'clearer images' than another.

That is correct, but again, I've seen many instances...more often than not...where much of the extra height within a 4x3 image is wasted on sky or high ceiling space anyway. If a certain FoV width is required and the 16x9 aspect ratio doesn't capture the necessary FoV height, then I would argue the need to move to a 3mp (or 3.1 depending on the manufacturer) in order to maintain the same pixels per foot, or image clarity.

Just to clarify, is the horse dead enough yet? :-)

We have test results on 16:9 vs 4:3 aspect ratios. See Aspect Ratio 16:9 vs 4:3 Shootout. From those results, I was surprised about how many situations I did see benefits from the 'taller' 4:3 aspect ratio.

The simple answer to wasting it on 'sky or high ceiling space' is to tilt in down and to get more of the near field FoV.

Great article! I stand corrected, though I do still maintain that using the HD standard terms (720p, 1080p, 4k) is preferable when applicable since it encompasses more than just resolution (aspect ratio, frame rate), then MP (3mp, 5mp, 40mp, etc.) when the HD standard doesn't apply.

By the way, I gotta say that I do appreciate your attention to details and not letting the little things go. I did learn something from this exercise, and that's always valuable.

Thanks.

I agree there's value in using HD standard terms. The problem, as we discussed early in the original post, is that lots of manufacturers who use those terms don't meet the standard (e.g., the Avigilon 4K's frame rate). Then you get into how many frames one really needs :)

Typo in the "K" paragraph of the article:

"columns (P) and rows (K)"

Based on the prior paragraph, "p" (480p, 720p, 1080p) refers to rows. Feel free to delete this when corrected.

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