Digital Photo Noise - Photo Noise Reduction
Many people have unreasonable expectations of digital photography. They may feel that digital photos should be
perfect in terms of colour and detail. In fact, numerous problems can crop up - some of them are an inherent part
of the digital domain, while others can be caused by improper settings of the digital camera.
Noise on a digital photo is determined to be any part of a digital image that was not existing in the original
scene. It is likely to show as specks in the photograph, pale areas of white, or blotchy patches where there should
be an uniform gradation of shade.
Conventional photographs also possess imperfections but these have become an acceptable part of that medium. For
instance, grain on the actual film emulsion is a pattern of noise which is often used for artistic effect. However,
when it comes to digital photography, peoples expectations are much higher in respect of noise. Although it is true
that digital camera images should be much cleaner than film, other factors such as electronic noise come into
Electronic noise in digital photography comes about during the process of converting light into digital numbers.
The individual photo-sites that make up an image sensor function by converting photons into electrons and this
conversion can produce unwanted artifacts due to the haphazard way that photons arrive at the photo-sites.
Amplification of the electrical signal from each photo-site can also generate it's own form of noise. Because
the electrical charge is so tiny it must be amplified to a usable level. The noise produced during amplification
can be regarded of as static and is comparable to that found on radio broadcasts, although in this instance the
static produces visual artifacts instead of audible noise.
Photo Noise Reduction
Noise becomes most evident when photographs are taken using extended exposure times or high ISO settings.
However, there are a number of things that you can do to reduce this noise to a minimum. In conventional
photography, ISO settings are a function of film speed. Using a high speed film, it is possible to capture images
at very short exposure times which is ideal for photographs taken where there is fast movement such as an athletics
event. However, high ISO settings in digital cameras produce more noise than low ISO settings.
Another source of noise can be long exposure times which are most often used to take pictures in low light
conditions such as low light interiors. As a rule of thumb, try keeping ISO settings low and exposure times short
which in turn should minimise noise as you take photographs.
Removing Photographic Noise
There are a number of software packages which have been specifically designed to remove noise from digital
photographs. The software works by applying camera profiles to reduce noise on photographs taken by specific
digital camera models. However, because of the seemingly random nature of noise artifacts, these profiles will
never exactly match the noise produced by your specific camera.
One technique that you can carry out yourself is to produce your own noise profile for your camera. To do this,
take your first photograph as normal and then take another photo immediately after the first and with the same
camera settings. This second picture must be completely black so the camera shutter should be closed, the
viewfinder covered and ideally, the camera placed in a bag, so that no light enters the camera body.
As this second photograph will almost exactly match the noise of the first photograph, you can then use it as a
noise profile in photo editing software such as Photoshop to remove the noise from the first photograph. For best
results, this technique should be used on uncompressed files such as RAW or TiFF . However, it will also work with
JPEG files if that is the format the image has been saved in.