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We all know where digital noise in image files comes from, don’t we? Accumulative noise increases with long digital exposures under low-light conditions and at high ISO, a typical night photography scenario. Noise is also more obvious in areas of underexposure and is spread across the frequency spectrum. Noise varies with color and brightness and it is different for every digital camera or scanner, but blue-channel noise is usually higher than in other channels and shadow noise is typically higher than brighter areas.
Like film grain, digital noise has many internal causes: Dark noise is produced by heat from the camera’s sensor during capture, and is collected along with the data from light passing through the lens. Random noise is created by fluctuations within the camera’s circuitry or even from electromagnetic waves outside (more later) the camera. Signal noise is caused by fluctuations in the distribution of how light strikes an image sensor. Amplified noise is caused by high ISO speeds and is the digital equivalent of “pushing” film to achieve greater light sensitivity.
There are also several sources of external noise, including “pixel death” rate that is more pronounced at higher altitudes such as where I live. Then there’s the Taos Hum perhaps? Now before you think you’re reading the script from a rejected episode of “The X Files” think about this:
Sunspots are an intensely magnetic area on the Sun’s visible face that is slightly cooler than the surrounding photosphere. It may be because the magnetic field interferes with the outflow of solar heat in that region, and therefore appears a bit darker or not. Ask Stephen Hawking, not me. Sunspots tend to be associated with violent solar outbursts of all kinds and the number of spots varies according to the Sun’s 11-year cycle. Bottom line, scientists analyze hot pixels to measure the effects of solar particles and cosmic rays on digital images. Based on this, one could extrapolate that sunspots indirectly cause hot pixels due to the solar particles and cosmic rays they generate.
Here’s a few tip you can take to reduce noise before making a digital photograph:
1) Photographers should avoid placing external battery packs too close to their digital cameras. Some of these packs contain transformers that raise voltage levels for faster flash recycling, while emitting electromagnetic interference at the same time. This can result in severe degradation of digital image quality, with heavy banding effects. In such cases, the best workaround is to carry the battery pack on a belt or a photo vest while connecting it to the flash unit via cable.
2) Photographers should also avoid taking pictures close to other strong sources of electromagnetic energy. I have been told that it’s quite common to see banding in digital images shot from the observation deck at the Empire State Building in NYC due to the presence of the strong antennas at the top of the building. Similar situations can occur in sports photography when the photographer is standing too close to a TV camera crew that is using a microwave dish to transmit the video feed back to their base station.
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