slow shutter speeds: when the shutter is kept open for a long time more noise will be introduced to the photo. A slow shutter speed translates to the CCD integrating more light per pixel. The effect can be easily understood as the CCD “accumulating” light in each pixel and measuring the total light over the shutter period of time. However at the same time the CCD is also “accumulating” noise. For that reason in slow shutter speed photos some pixels will appear as noise because for these pixels the amount of noise integrated is significantly close to or higher than the actual light measured.

high sensitivity modes: high sensitivity in digital photography is implemented by mechanisms that result in amplification. The CCD amplifies the measurements it takes. However there is no way to just amplify the actual photo light that falls on the CCD pixels instead the noise and the actual light are both amplified. The result is that the CCD becomes sensitive not only to light but also to its own noise. When too much amplification is applied some pixels will appear as noise.

While it is impossible to completely prevent digital noise there are a few options that allow you to significantly decrease it. When taking photos in low light scenarios such as night photos there are two main parameters to play with: sensitivity and shutter speed. Raising sensitivity creates more internal noise in the CCD while slowing down the shutter allows for more noise to integrate on the CCD. The amount of noise generated by both parameters is different. It is recommended that you set your camera to manual mode and play with a few different sensitivity/shutter speed pairs to find out the one that generates the least noise.