Beware Imager vs Stream Resolution

Author: Ethan Ace, Published on Sep 10, 2015

Typically, a camera's sensor resolution and stream resolution are the same. So a camera with a 3MP imager supports a 3MP stream max.

However, sometimes the actual stream resolution supported is significantly less than the imager resolution. Worse, some manufacturers try to obscure this to make their cameras look higher resolution, causing confusion and disappointment for users.

Panoramic cameras are the most common example of this problem. In this note, we explain the differences and the risks involved.

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Comments (10)

Thank you Ethan for pointing this topic!

Question: are there panoramic cameras with, for example, 5MP sensor (quite typicall now), but with only 2MP stream (panoramic or de-warped soft PTZ)?

The Axis M3007 comes to mind. It uses a 5MP sensor, but aside from the fisheye overview stream (5MP) it outputs much lower resolutions. For example, the dual panorama and PTZ view areas are both 1920x1440 max resolution, about 2.7MP. There are other examples but that one I know off the top of my head.

The main argument for this is that these streams are removing unnecessary regions from the image (like the black around the spherical view) or looking at only a portion of it, and that's why they are lower resolution. But it is still often deceptive and can be difficult to calculate.

There are other examples...

Same deal noted here after the test of Panasonic panoramic, yes?

  • This size of the camera's sensor is 12 MP.
  • The fisheye lens forms an image circle of 9 MP.
  • The images in the test are 5 MP.

Camera from your example is fair - it is still delivering sensor pixel-2-pixel. And other streams really do not need full resolution.

Any ideas about cameras where original imager(s) is/are completely obscured? Scallop maybe?

I have a mix of the geovision FE and Vivotek FE cameras, and have verified the above statement. I battled this on install but gave up on it...so I have to wonder if these 5mp FE cams are only putting out 3mp, if you buy the 3mp fe, will the image be scaled again or will it be 3mp.

Heres a snapshot of Geovision software stating the actual size of 1920*1920, the camera is a vivotek being ran on the geovision platform.

Some manufacturers crop the camera's image to a square aspect ratio to eliminate the wasted black space seen above. For example, a 5MP camera (2592x1920) may be cropped to 1920x1920.

1920x1920 = 3.7MP

And even that number is deceiving, the effective pixels are actually more like 2.9MP.

Ethan, do any of these new panoramics have lens options that might change the image circle, and therefore the amount of wasted pixels? I think I have a Mobotix that does, but it's old.

Off-topic, but I have to ask, what is all the debris and downed signage in the middle of the street? Was there an accident or a wind storm?

The intersection where we were shooting is pretty infamous here. The road to the right leads to what was supposed to be a shopping center but it was never built. There are parking lots and much of the site is paved, but no buildings. The debris is the road closed sign which was already on the ground when we got there, and broken sandbags which were holding it. Fun fact: this was the only site I was ever asked to leave by the police. The site is private property but we were on the sidewalk which is public. He asked me to go anyway.

The site is private property but we were on the sidewalk which is public. He asked me to go anyway.

The trunk being open gives the impression you were ready to high tail it out of there if necessary. ;)

I think this may be one of the worst offenders, the Dahua "12MP" fisheye.

Not only is it marketed as 12MP, the spec sheet lists the resolution as 4000x3000. Effective pixels.

The other ones don't seem to actually state a bogus stream resolution as well.

I don't know how many it does use, but it's not possible to have a fisheye with a resolution as high as the sensor unless the sensor is round, or you are including dark pixels, right?

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