Image Sensor Sensitivity and Noise
Click to see the effects of increasing ISO.
Click to see the effect of noise in an image.
In some situations images are not as clear as they otherwise are. They appear grainy with randomly scattered colored pixels that break up smooth areas. This is what's known as noise. It has three basic causes:
- Small photosites on the sensor. There is nothing you can do about this cause, but it also makes the following causes even more severe.
- A long shutter speed that lets light into the camera for a long time, usually in a dim or dark setting, gives noise a chance to build up.
- A high ISO setting let’s you use a faster shutter speed to avoid blur but also amplifies the noise along with the signal.
Many cameras have one or more noise reduction modes that reduce the effects of this noise.
Noise appears in images as random color pixels especially when you use long shutter speeds or high ISO settings.
At slow shutter speeds (left) the exposure, like dripping water, is so slow noise has a chance to build up in the image. At faster speeds, (middle and right), the noise is overwhelmed by how fast the exposure is completed.
To see one kind of noise, leave the lens cap on and take a picture. The long exposure will create noise that you can see when you open the picture in a photo editing program and enlarge it.