Two nights ago was full moon. I looked out the window and there it was, bright and round, and illuminating the edges of the clouds surrounding it. What a nice sight, I thought, and snapped a few shots just as the clouds started to obscure it. When I downloaded the images and viewed them all at full size, I found some bright dots which I initially thought were stars. However, the same dots appeared in all the other images as well ? same colour, same spot. A search with Google revealed that these are hot pixels.
Hot pixels are those that appear as bright dots in the image in long exposure, especially in low light and night shots. The CCD, which captures the image, consists of millions of light sensitive elements. Hot pixels usually occur when the CCD is heated up after prolonged use, resulting in charge leakage in some of the sensors. This makes the particular pixel brighter than the surrounding ones and shows up as white, red or green dots in an otherwise dark background.
Most if not all digital cameras have hot pixels. This anomaly can be removed by remapping the CCD. Remapping simply hides the odd pixels by masking it with the colours of the adjacent pixels. The camera has to be sent back to the manufacturer to be remapped. It can also be reduced by using the noise reduction feature available in most digital cameras. For the moment, I can live with those odd dots which appear only in images taken with slower shutter speeds. These defects are nothing that photo editing software cannot correct.
Apart from hot pixels, the CCD is also plagued with stuck pixels and dead pixels. In stuck pixels, the particular sensor is always on, producing a bright dot irrespective of shutter speed and aperture size. This usually appear as red, green or blue in the image. Dead pixels appear as black dots because the sensor is always off, thus not registering any light. This normally turn up as black dots in images taken in bright condition.
The LCD screens are also afflicted by these defects. This is unavoidable because the elements weaken as they age and start to malfunction. I have no complaints regarding this problem as this Nikon Coolpix 3100 has served me well, having captured over two thousand images and is still doing fine generally. The only gripe I have is that the battery power is exhausted fairly quickly and I usually have to carry a few set of spares every time I go out on a shooting spree.
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