Megapixel or Speed Dome?




Suppose you had installed an analog speed dome camera with 35X optical zoom, viewing the entire area of a parking lot when it is at its maximum aperture (3.6 mm - 68°). If you want to see some detail, just position the camera and zoom, taking the lens aperture from 3.6 mm to 126 mm.


At the the same situation, if you had installed a megapixel camera, with a lens covering the same 68° angle,  you would also could see the entire parking area and if you wanted to see some detail, it would be suffice to perform a digital zoom in the image, viewing the detail without losing recording the total area.


This is one of the most used selling arguments  to convince a customer to buy a megapixel camera instead of a speed dome, since the latter when zooms in to catch some detail, fails to show (and record) the rest of the scene .


However, analog speed dome cameras always display and record in D1 resolution (720 x 480), regardless of the lens aperture - the level of optical zoom.


In the example at left, visualized area with optical zoom at maximum is 35 times smaller, but resolution is maintained.


For a fixed lens camera, how many megapixels would be needed in order to have same field of view and resolution as a speed dome camera in its maximum optical zoom?


This camera must have to present an image with a resolution of 720 x 480 pixels at a digital zoom of 35 times.


Multiplying horizontal and vertical resolution of the smallest area to be displayed (720 x 480) at the level of the needed digital zoom (35 X), we have:


Horizontal resolution: 720 x 35 = 25200 pixels


Vertical resolution: 480 x 35 = 16800 pixels


Total resolution: 25200 x 16800 = 423.36 megapixels!


So it would be needed a 423 Megapixel camera to take up same resolution of a speed dome camera in its 35 times optical zoom. Which is still impractical.


Just to make a comparison, the 29 Megapixel camera commented in the article "29 Megapixel IP Camera with 0.1 Lux minimum illumination?", which has a resolution of 6576 x 4384 pixels, can only go up to 9X Digital Zoom when displaying an image with a 720 x 480 pixels resolution. Above this level of zoom, its resolution would be worse than in an analog camera.


Moreover, another advantage of a speed dome camera is that it can cover around 360°, while a megapixel camera, although always capture the whole scene, would be limited to the opening angle of the chosen lens.




Weighing advantages and disadvantages of each solution, the best would be to use one or more fixed megapixel cameras in the areas to be observed - with a resolution enough to notice any suspicious movement - in conjunction with an analog speed dome camera, which would be used to obtain further details of the scene.


Note: This comparison was made with an analog speed dome camera. If a megapixel speed dome was used, situation would be worse for the fixed megapixel camera.


For example, a 2 megapixel speed dome camera at a 20 X optical zoom provides a total zoom of 120 X in D1 resolution...




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