As the camera resolution (total number of pixels) increases, so does the field of view at constant image resolution (pixels per foot). Table 3 below compares the field of view of different cameras at a distance of 32 feet from the subject at the same image resolution. Because the total available pixels spread across the field of view is greater, the field of view can be increased without decreasing image resolution. Table 2: As field of view increases the pixels per foot decreases so that each picture has the same number of pixels and thus causes the same amount of network loading.Īnother advantage of the higher resolution available from megapixel cameras is the ability to cover a much wider area with the same or better resolution compared to analog cameras. Identification (high detail) 60 200 Detection (general security) 20 70 Because there are no more pixels in one image compared to another, there is no effect on the amount of data transferred over the network and no degradation of network performance by going to either higher image resolution or greater field of view. Each image has the same number of pixels but as the field of view increases, the pixels per foot in the image decreases. In Table 2 below, an image is shown at different levels of resolution from “high detail” for clear identification at 60pix/ft to “motion tracking” for wide field of view at 10pix/ft. There is a balance that must be made between level of detail and project budget. However, higher detail requires higher resolution cameras or more cameras and thus more bandwidth and storage. The more pixels on a target, the higher the resolution will be and the more likely recognition and positive identification will be made. There is not yet an industry standard for the level of sharpness required in every video surveillance application. This is the definition that I will expand upon further in the rest of this white paper. This gives a pixels per foot number that can be related to image quality. Fundamentally it is the horizontal field of view (HFOV) of the camera divided by the horizontal number of pixels. This mapping of the image sensor dimensions onto the object is most intuitive for calculating what level of detail can be seen in the image. These high quality lenses, including those manufactured by Theia Technologies, are rated for megapixel or multi megapixel cameras meaning the image will be sharply in focus at the camera resolution it is rated for.ĭefinition 4: Resolution can be specified in pixels per foot or meter at the object. As the total number of pixels on an image sensor increases, the pixel size gets smaller and requires a higher quality lens to achieve best focus. At the image sensor resolution is expressed as line pairs per millimeter (lpm) commonly used by lens designers and optical engineers. Twice as much resolution in a 1080 HD cameras means twice as much detail or field of view compared to a 720 HD camera.ĭefinition 3: Resolution can be the level of detail with which an image can be reproduced or recorded. Table 1: Number of pixels for different megapixel camera formats. Megapixels Total number of pixels Vertical pixels Horizontal pixels Table 1 below shows examples of typical megapixel camera resolutions. With megapixel cameras, the resolution is generally the total number of pixels, divided by 1,000,000, and rounded off. The number of TV lines in the image can be 320, 480, 570, etc.ĭefinition 2: Resolution can be expressed as the total number of pixels. For analog cameras this is the usual definition. The greater the number of lines, the greater detail or larger field of view can be recorded with the camera. I’ll list only the definitions relevant to the video surveillance industry here.ĭefinition 1: Resolution can be expressed as the number of TV lines or pixels of the image sensor used to record an image. Resolution has many definitions no one definition is correct for all situations. Rectilinear lenses such as those using Theia Technologies’ Linear Optical Technology™ don’t exhibit barrel distortion and thus maintain image resolution out to the edge of the image. Greater than about 90? most lenses start to show curved, barrel distorted images that compress the image at the edges. The shorter the lens focal length, the wider the field of view. The detail in an image is determined by resolution.
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