Is there really a difference between high-definition (HD) cameras and megapixel devices? We asked two technically-oriented people active in the CCTV camera industry to give us their opinion of the HD vs megapixel debate – if indeed there really is a debate.
Reditron’s MJ Oosthuizen commented that HD cameras are just a different form of megapixel cameras. Below, his response on some of the differences between traditional HD and megapixel cameras.
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.
Picture aspect ratios
Similar to the image size, the aspect ratio of HD cameras is 16:9 whereas other megapixel 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 four 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?
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.
There is a wide range of megapixel cameras available today with selectable resolution and frame rates that are ideal for general surveillance applications. These options provide system designers with a high degree of flexibility and confidence in their designs. Sub streams for viewing across multiple stations allows flexible designs, while the highest resolution for reviewing can be utilised through a distributed storage architecture.
For video, there are three main fluctuating factors that contribute to bandwidth hogging of an IP camera – frame rate, resolution and compression. Any one of these factors can be throttled back to reduce the network bandwidth. For example, if you reduce the frame rate, you can increase the resolution, and vice versa.
Frames per second (FPS) describes the number of full video frames displayed or recorded within one second. Since each type of business varies, it is important to determine what requirements are needed to sustain certain defined performance parameters, such as frame rate.
Cable selection and bandwidth go hand-in-hand. Considerations when selecting the cable media include number of cameras, type of camera, location of the cameras (environment), distance to the server rooms, type of termination equipment, and whether power will be running through the cable (UTP).
Whether you prefer megapixel cameras or its subset HD based on your specific needs, the wide range of high resolution cameras today provides a powerful palette of imaging tools for industry professionals. It is crystal clear that better systems are a direct result of the superior imaging possible with these high-resolution camera technologies.
Miro comments
Alex Bantjes, Miro’s brand manager for Vivotek, also weighed in on the HD/megapixel debate. Bantjes says, “High definition and megapixel are often mistakenly thought to be the same and the terms are used interchangeably. Although both terms are closely related, there is in fact a distinct difference.”
High definition, or HD, is actually a result of the analogue broadcasting/CCTV camera industry. HD simply refers to a set of standards that are used to describe the image quality of a camera as displayed on a monitor. These standards include image size, aspect ratio, frame rate and scan type. For example, the description 720P refers to the horizontal resolution of the image (16:9) and the letter P indicates progressive scan.
An image stream is defined as megapixel once the image exceeds a million pixels. The term refers to any camera with a resolution of 1280x1024 (1.3 megapixel) or higher. It should also be noted that the term 720P is not in fact the same as one megapixel, since 720P (1280x720) actually has an image of nine hundred thousand pixels or 0,9 megapixels.
Modern surveillance systems are not exclusively used to display images on monitors or television screens, output streams are required in any number of aspect ratios, image resolutions, frame rates etc. Megapixel technology is much more flexible than HD in that each output stream can be defined to optimise video for slow transmission (such as the Internet) or smaller screens (table to cellphone).
The latest advanced technologies such as adaptive streaming, where the frame rate is lowered when there is no motion in the image and then sped up to capture details of moving objects, will by definition not be available in an HD stream but only in megapixel.
In short, megapixel based system design allows for more flexible surveillance systems that can be viewed on many different types of devices at varying frame rates and resolutions. HD on the other hand is often too restrictive to meet the requirements of today’s surveillance systems.
Definitions
High-definition
* Conforms better to multimedia systems, but resolution and image format choices are more limited.
* 16:9 image format.
* Two resolutions: HD (720p) and full HD (1080p), measured by pixels of vertical resolution.
* Maximum resolution: 2.1 megapixel.
* Progressive scanning: all lines in each frame are drawn in sequence.
* Frame rate: 25/30.
Megapixel
* One million or more pixels of resolution.
* Flexible image formats: 4:3, 5:4, etc.
* Flexible resolutions: 1 to 10 megapixels (or more).
* Maximum resolution: 20 megapixels.
* Frame rate: 3-15 frames per second – can run up to 30fps on lower MP rated cameras.
MJ Oosthuizen, Reditron
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