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What are the differences between HD and megapixel cameras?

Over the last year there has been an explosion in the number of manufacturers offering megapixel cameras, with many reaching over 3-megapixel. However, more recently there have been a number of cameras offering HD quality video footage in addition to their megapixel cameras.

What’s the difference?

Don’t think of megapixel and HD cameras as being two separate entities. HD cameras are just a special from of megapixel cameras which conforms to certain specifications laid out by the Society of Motion Picture and Television engineers (SMPTE). The HD specifications must all be met in order for a camera to be classed as an HD camera.

Image sizes

There are two main resolutions for the HD specification, 720p (1280×720, just less than 1-megapixel) and 1080p (1920×1080, 2.1-megapixel). Conventional megapixel cameras often have a number of megapixel resolutions to choose from. Image quality from HD cameras is therefore not as detailed as some other megapixel cameras.

Picture aspect ratios

Similar to the image size, the aspect ratio of HD cameras is 16:9 whereas other megapixel cameras cameras offer a variety of formats such as 4:3.

Frame Rates

This is the biggest advantage to HD cameras over megapixel cameras. Until recently, megapixel cameras have offered very low frame rates compared to low resolution cameras, sometimes offering as low as 4 frames per second compared to 30 frames per second. This has largely been due to processing power available on IP cameras as well as network restraints.

The HD standard requires footage to be created at 25 or 30 frames per second depending on location, for example the US runs at 30 frames per second while the UK runs at 25.

Progressive scan

Megapixel camera manufacturers have often used interlaced images to create megapixel footage. This essentially uses two frames to create the image. In the first frame, they capture lines 1, 3, 5, 7 etc with the second frame capture lines 2, 4, 6 etc. This can be manufactured cheaply but often causes blurred images when fast-moving objects are in view.

The HD standard requires that frames are progressively scanned. This is more expensive but provides a much clearer and crisper image.

Why does the HD format exist?

The HD format was created to try and standardise the video transmissions of megapixel cameras. With HD televisions also conforming to the standard, video output can be made to any HDTV without cropping or resizing.

The HD format has worked well in forcing camera manufacturers to increase processing power and the potential of their IP cameras but conversely it may also begin to limit the development of megapixel cameras. At present, high end megapixel cameras can be up to around 8-megapixel. If IP camera manufacturers begin to adopt the HD format for their cameras, the format will need to be updated to include higher and higher resolutions otherwise the extra detail possible at present will be lost.

Published on February 12th, 2010 by James Drinkwater

3 Responses to “What are the differences between HD and megapixel cameras?”

  1. Gary says:

    You are correct. The Q1755 is a 1080i camera, however, the P1346 is a 1080p camera. Either one is a very decent product.
    For my money, the cameras from Arecont are far better products. They offer a 5MP, 10MP as well as a 180 degree panoramic, and a 360 degree. This company only operates in the MP arena and are becoming the industry leader in that arena.

  2. James says:

    Hi Mike,
    You are correct that TV broadcasts offer the 1080i standard. However, most IP camera manufacturers do not consider interlaced images to be true HD due to the image "tearing" that can occur whenever there are fast-moving objects in view.
    There are a few 1080i cameras on the market but largely if manufacturers develop HD cameras they use progressive-scan sensors.

  3. Mike says:

    The article says the HD standard requires progressive scan but some of the TV HD broadcasts use 1080i. Is it a camera requirement but not a broadcast requirement?