The sensor in a digital camera is made up of 1,000’s of photo sensitive cells (pixels). To give you a rough idea how many, look at the megapixel rating for your camera – 18 megapixels roughly translates to 18 million cells!
When we refer to noise in digital photography, we are talking about image quality. Have you ever noticed that some of your images look very speckly, with a random pattern of dots and colour appearing? What you are seeing is the information recorded by the pixels. This is more noticeable in the dark areas of your image, or areas where there is a lot of one colour tone (see the picture shown above, where a small dark area has been enlarged to show the effect of noise and how it changes when the ISO is increased).
This is noise and it is caused by the amplification of the signal in electronic circuitry. If you think back to your first car stereo, we used to crank up the volume and in doing so this led to distortion. The quality of what we were listening to got progressively worse the more we turned up the volume.
It is the same in digital photography. The more we increase the ISO (the sensitivity of the sensor’s response to light), the more the image quality starts to degrade.
As a rule of thumb, it is always best to select the lowest possible ISO setting your camera will allow (50, 100 or 200 – depending on make and model) for the conditions you are shooting under. Remembering the slowest shutter speed you can safely handhold your camera. It is far better to have a sharp noisy image rather than a blurry low noise one – noise can be dealt with in post-production.
As digital technology improves, the cameras being produced today have a far better noise capability at high ISO settings compared to those that were produced just a few years ago. Some high-end professional cameras even record good quality up to 6400 or even 12800 ISO (and beyond) and some can even expand their ISO range to 204800.
Even if you have an image that suffers from noise, software products like Adobe Lightroom and Noise Ninja, allow you to more or less eliminate the noise without degrading the final image in post production.
We cover this topic and also the various ISO settings in our Getting Started course.