You can adjust your camera’s ISO sensitivity in low-light shots to reduce the exposure time and lessen the risk of camera shake. When using a flash or in bright settings, keep the ISO setting to its lowest possible value.
At higher ISO settings, the camera sensor amplifies the signal and ends up ‘inventing’ pixels which would ordinarily not be visible. This creates ‘noise’, as the signal-to-noise ratio deteriorates, which equates to graininess in analogue photography. The problem isn’t really visible at low ISO values (100-200), in small prints or daylight photography, but noise becomes a major issue, especially in compact cameras and low-end dSLRs in low light shots at anything above ISO 400.
Below is an example of noise at a very high ISO value (3200) taken with a Canon 5D mk II.
Although this camera’s high ISO capability is very good, you can see that image quality has suffered. Textures are ‘mottled’ and surfaces break down into coloured dots.
In compact cameras and the JPG setting on dSLRs, there are very few choices to fix this problem. All too often, your camera will over-compensate with noise reduction algorithms and introduce other problems by over-sharpening. You have a bit more latitude if you shoot in RAW.
There are also professional-grade (and expensive) applications available, such as Noise Ninja, which tackle this specific issue. Other applications, including the ones shipped with your camera, also include noise-reduction tools.
Below is a quick and nasty tool I learnt if you use Photoshop.
1. Click on the Channels tab next to the Layers tab
2. Click on the second channel (red)
3. Go to Filters > Noise > Despeckle
4. Press ctrl/cmd + F to repeat this process once
5. Click on the next channel (green) and press ctrl/cmd + F twice
6. Click on the final channel (blue) and ctrl/cmd + F four times (blue is the prevalent colour in most shots and needs more work)
7. Click on the composite RBG channel to restore your colours and continue editing
This method considerably softens your image, which will therefore require more sharpening afterwards.
Below is the despeckled image.
The image is softer but the noise has been considerably reduced.
