Don’t Let Noise Kill Your Images
Cornwall, October 2011
Copyright: Robin Whalley 2011
One of the complaints that has dogged small and compact cameras in the past is that they are prone to noise and noise can kill images dead. Unfortunately, whilst advances have been made, these cameras by virtue of their smaller sensors can still have problems. So what to do?
The first thing to realise is that not all image noise is the same or has the same negative impact on the final image. Colour noise appears as random colour speckles in the image and can result in images that appear “muddy” and ultimately lose definition and detail. This noise is quite ugly and should be removed whilst trying to do as little damage as possible to the image.
Luminosity noise appears as speckles of light and dark areas on the image and resembles film grain. If you remove all of this noise your images can look a little “plastic” like. If you have too much of this noise in your images you can lose the definition and they don’t appear sharp. But if you have a small amount of this noise it can actual make your images appear more detailed and sharper when printed.
The best approach is not to try to remove the noise from your images but to avoid introducing the noise in the first place. And as smaller sensor lightweight cameras have smaller sensors that are more susceptible to noise, you need to consider some of these strategies:
- Keep ISO’s low. Don’t rely on having your camera ISO set to auto. Yes it will increase the ISO when light is low to avoid slow shutter speeds but it will probably do this much too early.
- Use your camera in Aperture Priority mode where you select the aperture to determine the depth of field and the camera calculates the shutter speed. See next point for why.
- Consider how much depth of field you really need and what is the widest aperture to allow this. With small sensor cameras you will find you can use a much wider aperture to achieve a given depth of field. A wider aperture means more light reaching the sensor which means faster shutter speeds so you can use lower ISO settings.
- Shoot in RAW. You can then take control of the level of noise reduction applied to the final image. With most RAW converters you can even apply different levels of colour and luminance noise reductions to suit your image.
- Use a monopod in low light. This allows you to use slower shutter speeds without the need to increase the ISO.
- Expose the image to the right in the histogram. To use this approach you really need to be shooting RAW format but the technique involves slightly overexposing your images by perhaps 2/3 of a stop.
- Try to avoid long exposures if possible. Over about a second the sensor will warm up and create noise.
Whilst cameras have improved greatly in their handling of noise the above techniques are still valid and will help you create a quality image.