| Digital noise in photos taken with digital cameras is | | | | on the CCD pixels instead the noise and the actual light |
| random pixels scattered all over the photo. It is a similar | | | | are both amplified. The result is that the CCD |
| effect as "grain" in film photography and it degrades | | | | becomes sensitive not only to light but also to its own |
| the photo quality. | | | | noise. When too much amplification is applied some |
| Digital noise usually occurs when you take low light | | | | pixels will appear as noise. |
| photos (such as night photos or indoor dark scenes) or | | | | While it is impossible to completely prevent digital noise |
| you use very slow shutter speeds or very high | | | | there are a few options that allow you to significantly |
| sensitivity modes. | | | | decrease it. When taking photos in low light scenarios |
| When taking pictures with a digital camera an | | | | such as night photos there are two main parameters |
| electronic sensor (also known as a CCD) built from | | | | to play with: sensitivity and shutter speed. Raising |
| many tiny pixels is used to measure the light for each | | | | sensitivity creates more internal noise in the CCD while |
| pixel. The result is a matrix of pixels that represent the | | | | slowing down the shutter allows for more noise to |
| photo. | | | | integrate on the CCD. The amount of noise generated |
| As with any other electronic sensor the CCD is not | | | | by both parameters is different. It is recommended |
| perfect and includes some noise (also know as white | | | | that you set your camera to manual mode and play |
| noise to hint on its randomness attribute). In most | | | | with a few different sensitivity/shutter speed pairs to |
| lighting the light is significantly stronger than the noise. | | | | find out the one that generates the least noise. |
| However in extreme scenes where the light is very | | | | Some cameras include a built-in feature called "noise |
| low or when a high amplification is needed noise levels | | | | reduction". Noise reduction is implemented by |
| can become significant and result in pixels in the | | | | sophisticated software that can identify the noise |
| photos that include more noise data than real photo | | | | pixels and remove them. For example the software |
| light data. Those pixels usually appear as random dots | | | | can identify the noise pixels based on their |
| or stains on the photo (for example white dots | | | | randomness and usually extreme intensity gap |
| scattered randomly on the photo). | | | | between them and their neighboring pixels. Removing |
| Understanding digital noise in various scenes:low light | | | | the noise can be implemented by interpolating a |
| (night photos or dark scenes): when the scene is dark | | | | replacement pixel value based on its neighboring pixels. |
| the amount of light measured by each pixel of the | | | | If you do not have a built-in noise reduction feature or it |
| CCD is low. When the light intensity is very low it can | | | | does not work properly you can use a PC based |
| become too close to the level of noise naturally found | | | | software that removes digital noise. Many photo |
| in the CCD. In such cases some pixels can appear as | | | | processing software include a combination of |
| noise because the noise level measured for them is | | | | automatic and manual digital noise removal. Some |
| significantly close or higher than the actual light | | | | software packages can also use a few photos of the |
| intensity.slow shutter speeds: when the shutter is kept | | | | same object to "average" them and thus remove the |
| open for a long time more noise will be introduced to | | | | noise (relying on the fact that digital noise is random |
| the photo. A slow shutter speed translates to the CCD | | | | and the noise pixels will be different in each photo |
| integrating more light per pixel. The effect can be | | | | taken). |
| easily understood as the CCD "accumulating" light in | | | | To conclude digital noise should be understood by any |
| each pixel and measuring the total light over the | | | | amateur or professional photographer. However for |
| shutter period of time. However at the same time the | | | | most photographers digital noise is not a practical |
| CCD is also "accumulating" noise. For that reason in | | | | problem even in low light scenarios usually digital noise |
| slow shutter speed photos some pixels will appear as | | | | is minimal and can be significantly reduced by simply |
| noise because for these pixels the amount of noise | | | | turning on your camera's noise reduction feature. For |
| integrated is significantly close to or higher than the | | | | professional photographers who shoot in more |
| actual light measured.high sensitivity modes: high | | | | extreme conditions digital noise can present a real |
| sensitivity in digital photography is implemented by | | | | problem and can be dealt with using a combination of |
| mechanisms that result in amplification. The CCD | | | | optimizing the camera settings and removing noise |
| amplifies the measurements it takes. However there is | | | | with professional software. |
| no way to just amplify the actual photo light that falls | | | | |