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The Effects of Over-Exposure in A Digital Image

An over exposed digital image is similar to the effect seen with any photograph. The picture will appear washed out and detail is lost. Once lost it cannot be recovered. The reason has to do with the digital process. Digital imaging established a digital value between 0 and 255 (00 to FF Hexadecimal) for each pixel based on the intensity of the light received by the camera. No value greater than 255 can be processed; should a greater value be encountered the camera adjusts it "255" and stores it in memory at that value. (Likewise any value less than 0 is assigned a zero.) This is due to the fact that each value is represented by an 8 Bit value and only 255 unique values exist in an 8 bit format. No overflow is permitted. Anything over that is called saturation or over-exposure.

Three pictures are shown here. The first image is a picture of the moon, properly rendered, with a normal exposure setting. (While it may appear to be too dark at first glance, note the bright features on the top left. A pixel weight scan proves these are at 95% of saturation.) The second image is over-exposed. While it may appear brighter, notice how the detail of the moon is lost. Depending on the degree of over-exposure the disk of the moon itself could be lost, but for illustration purposes I have kept it this level. A scan across this bright area shows over half of it is fully saturated with a value of 255. There is no detail remaining to recover. Many believe that the image could be darkened and the detail restored. The third image is just that, an attempt to recover the original image from the over-exposed version. Clearly the detail was lost. This is why attempts to process light in the sky UFO pictures usually fail to bring out detail. The fix for this is to adjust your camera settings when you take the picture. Either shorten the shutter time or adjust the aperture of the camera to allow less light to enter the camera.

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© April 2024 - J Brown