Progressive Scan Video


Normal video recording systems rely on fooling the eye by providing a rapid series of still images in turn on the screen, this basic technique is further enhanced by actually shooting and showing two sequential images on the screen at the same time - a technique called interleaving, each alternate horizontal line of pixels showing one of the pair of images. By doing this the motion flicker is reduced and a more convincing smooth flow of motion is obtained.

The drawback is that if the footage contains potential evidence and it becomes necessary to 'grab' a still of the anomaly or freeze the TV picture there may be blurring or distortion of the picture which is in reality two pictures woven together electronically. Some image editing software packages allow the option to 'De-Interleave' the image but this is also a compromise option and results in often not very satisfactory stills being available for analysis and interpretation.

Most camcorders record their images using an interleaved technique - 1st all the odd numbered horizontal lines of pixels are sampled, followed by the even numbered horizontal lines thereby effectively recording two images simultaneously. This has the added disadvantage that only half the vertical resolution of the chip is used for any single image.

Another technique that is borrowed from high end video cameras is the ability to use the whole chip to make a single image scan then repeating the process 25 times per second. This has the advantage of better colour saturation and image definition as there are many more pixels being used for each separate image. The downside is that any movement can appear slightly jerky or a little awkward.

But for those who are using video cameras to attempt to capture some anomalous object and then analyse it afterwards using a computer Progressive Scan allows much better stills to be obtained - sharper and more defined. Such a feature can become a valuable tool to the paranormal investigator.

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