Standard video resolutions uncovered: part 2

Megapixel and HDTV resolutions produce higher quality images

What are the benefits of Megapixel and HDTV resolutions? In part 2 of this article, Phil Doyle, Managing Director (UK & Ireland) of Axis Communications continues with an in depth explanation of their key advantages. (Read part 1 of this article on standard video resolutions)

Megapixel resolutions

A network camera that offers megapixel resolution uses a megapixel sensor to deliver an image that contains one million or more pixels. The more pixels a sensor has, the greater the potential it has for capturing finer details and for producing a higher quality image. Megapixel network cameras can be used to allow users to see more details (ideal for identification of people and objects) or to view a larger area of a scene. This benefit is an important consideration in video surveillance applications.

Here are some megapixel formats:

Display format	No. of pixels	Pixels
SXGA	1.3 megapixels	1280x1024
SXGA+(EXGA)	1.4 megapixels	1400x1050
UXGA	1.9 megapixels	1600x1200
WUXGA	2.3 megapixels	1920x1200
QXGA	3.1 megapixels	2048x1536
WQXGA	4.1 megapixels	2560x1600
QSXGA	5.2 megapixels	2560x2048

Megapixel resolution is one area in which network cameras excel over analogue cameras. The maximum resolution a conventional analogue camera can provide after the video signal has been digitized in a digital video recorder or a video encoder is D1, which is 720x480 pixels (NTSC) or 720x576 pixels (PAL). The D1 resolution corresponds to a maximum of

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Illustration of 4:3 and 16:9 aspect ratios

414,720 pixels or 0.4 megapixel. By comparison, a common megapixel format of 1280x1024 pixels gives a 1.3-megapixel resolution. This is more than 3 times the resolution that can be provided by analogue CCTV cameras. Network cameras with 2-megapixel and 3-megapixel resolutions are also available, and even higher resolutions are expected in the future.

Megapixel resolution also provides a greater degree of flexibility in terms of being able to provide images with different aspect ratios. (Aspect ratio is the ratio of the width of an image to its height.) A conventional TV monitor displays an image with an aspect ratio of 4:3. The advantage of a 16:9 aspect ratio is that unimportant details, usually located in the upper and lower part of a conventional-sized image, are not present and therefore, bandwidth and storage requirements can be reduced.

High-definition television (HDTV) resolutions

HDTV provides up to five times higher resolution than standard analogue TV. HDTV also has better colour fidelity and a 16:9 format. Defined by SMPTE (Society of Motion Picture and Television Engineers), the two most important HDTV standards are SMPTE 296M and SMPTE 274M.

Megapixel and HDTV resolutions are ideal for identification of people and objects

SMPTE 296M (HDTV 720P) defines a resolution of 1280x720 pixels with high colour fidelity in a 16:9 format using progressive scanning at 25/30 Hertz (Hz), which corresponds to 25 or 30 frames per second depending on the country, and at 50/60 Hz (50/60 frames per second).
SMPTE 274M (HDTV 1080) defines a resolution of 1920x1080 pixels with high colour fidelity in a 16:9 format using either interlaced or progressive scanning at 25/30 Hz and 50/60Hz.

A camera that complies with the SMPTE standards indicates adherence to HDTV quality and should provide all the benefits of HDTV in resolution, colour fidelity and frame rate.

The HDTV standard is based on square pixels-similar to computer screens, so HDTV video from network video products can be shown on either HDTV screens or standard computer monitors. With progressive scan HDTV video, no conversion or deinterlacing technique needs to be applied when the video is to be processed by a computer or displayed on a computer screen.

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