Wednesday, April 8, 2009

Quadruple the resolution?

Just received an email from a global IP camera player reminding me that they've released their 1.25 megapixel IP security camera. What confused me was this statement "...the user can see an image at four times the resolution of standard IP network cameras."

Assuming that a typical NTSC IP camera is about 0.33MP (704x480=338,000) then indeed 1.25MP is four times this number. But four times the resolution? I thought they doubled the width and doubled the height. That's double the resolution (in both directions). In some people's apparent eagerness to put a bullet in the head of not only analog cameras but also NTSC IP cameras, let's not forget the basics.

I used to think that resolution was related to my ability to resolve two very close parallel lines. Evidently image quality is being taught to be nothing more than a function of the number of pixels. I guess cameras in PDAs and cell phones are helping to propagate this myth. Maybe there's an emerging market segment that doesn't know, or possibly simply doesn't care.

As Jack Gin of Extreme once put it, and I'm adapting it to suit my purpose - would you rather have 333,000 bright pixels or 5 million dim ones. Same light, less surface area. And please don't brainwash me with the AGC nonsense - you're adding more noise, driving up my bit rate and storage costs and my video analytics won't work any more because of all those nasty nasty ants crawling all over my screen. At least let's hope people use decent visible lighting, and if that's proving unacceptable consider IR - it works wonders.

2 comments:

John Honovich said...

Hi Dr. Bob,

I agree with you. The statement you choose is actually one of the least extreme claims. I have seen manufacturers claim 80x the resolution (assuming 5 Megapixel cameras and maximum CIF for analog). This is doubly misleading.

In my analysis, like yours, I always use the horizontal percentage increase as a metric. For instance, a 5MP camera is 4x the resolution of analog (because 5MP cameras generally have 2592 horizontal resolution).

It makes me happy to see Bosch uncovering misleading marketing ;)

Great post!

John

Matt said...

Just a few commments on this issue.

Resolution is indeed the number of pixels you have in your image. At least that is how resolution is calculated in the IP world. The old analog world was all about TVL.

The comment made about 5 million dim pixels vs. 333,000 bright ones may have worked back when IP Megapixel was first developed, but through the years severe advancments have been made, and the low light performance of multi-megapixel technology is very good, if not great (this is assuming you are buying cameras from a reputable company who tailors to industrial and Enterprise security. It is true, however, that with naturally smaller pixels and many more of them in the scene, additional noise can in fact be present in the scene that may not be present under the same conditions from a lower resolution camera.

The other consideration that must be made here is what detail you getting at your 'object of interest'. I would rather see a slightly darker, but clear image of someones face or a license plate, than a nice bright blob that cannot be recognized in any way.