What's the difference between HD and Megapixel Cameras?

By John Honovich, Published Jan 29, 2009, 07:00pm EST

While 2009 was the year of megapixel surveillance cameras, it was also the year where confusion between HD and megapixel cameras began. Historically, everyone who sold cameras with 1 million pixels or more called them megapixel cameras. However, in the last 6 months, a number of manufacturers have begun touting their new megapixel cameras as HD.

Indeed, Axis emphasizes HD, rather than megapixel in its marketing, causing many to ask what is the difference and which is better?

HD vs. Megapixel

HD is a type of megapixel camera.  All HD cameras are megapixel but not all megapixel cameras are HD.

While standard definition cameras (e.g., analog cameras and 4CIF IP cameras) have no more than 400,000 pixels, all megapixel cameras (including HD) have 1,000,000 or more pixels.

HD's Key Features Compared to Typical Megapixel

The key features of HD for video surveillance is:

  • Maximum HD resolution is 2.1MP, maximum megapixel resolution is 20MP or more with 5MP cameras are common from numerous vendors
  • HD video format is 1280 x 720 or 1920 x 1080 (megapixel cameras can offer many more formats)
  • HD aspect ratio is 16:9 (compared to 5:4 or 4:3 in other surveillance cameras)
  • HD frame rate is 30/25 (where megapixel cameras are often 3 - 15 frames)
  • HDTV has quality compliance standards (where megapixel simply specifies the number of pixels)
Which is Better?
 
This is not a clear cut case - it will depend on applications. Some applications really need more than 2.1MP (the maximum for HDTV today) and do not need high frame rates (those should choose non-HD megapixel cameras). Other applications will care more about high frame rate and maximum image quality (where HD cameras will be best).
 

For most surveillance applications, the 16:9 aspect ratio of HD cameras will be more efficient to the 5:4 aspect of traditional megapixel cameras. 

In surveillance, you generally need to view far wider than you need to see high. The reason is that people and vehicles are only so tall but they can be anywhere across a wide area.

However, this does not mean you have to use a HDTV camera. For instance, if you use a 3MP camera (2048 x 1536), crop the bottom and top and have the same effective aspect ratio and resolution of a 1080p HDTV camera. Additionally, this camera may be also be less expensive than a 1080p HDTV camera.

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Frame Rate

Most applications are fine with 12 frames or less, which is quite typical for 3MP cameras. While a lot of attention will be drawn to 'full frame rate', the reality is surveillance applications have traditionally used far fewer frames per second and been successful at doing.

On the other hand, there will be certain applications (like casinos or money counting) where milliseconds count. A 12 frame per second camera provides an image every 83 milliseconds; A 30 frame per second camera every 33 milliseconds. An HDTV camera cuts out 50 ms. Only in circumstances where very fast tiny movements are key will HDTV make a difference.

Video Quality - Comparing Axis to Cisco

The aspect that concerns me the most about HDTV marketing is the implicit claims to HD TV quality. For instance, I saw the Axis HD camera at Intersec and the image quality was beautiful. By contrast, I saw the Cisco 1080p HD camera at ASIS and it looked like a webcam. Of course, it's just trade shows but it's reasonable to assume that not all companies who market HD cameras are going to produce the same quality.

Cost

So far the 1080p HD cameras are being priced at a significant premium to traditional 3MP cameras. Axis MSRP is $1495. Cisco's HD camera is $1400. Contrast this to an Arecont 3MP H.264 which sells on the Internet for less than $900 and probably MSRPs at no greater than $1100. Is a 30% premium worth it?

Marketing of HD Cameras Here to Stay

Given Axis' market power and the general appeal of HDTV, the branding of HD surveillance cameras is almost certainly hear to stay.  Though it will certainly cause confusion, everyone is going to have adapt to this new emphasis, either through matching HD products or enhanced education of tradeoffs/alternatives.

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