Make no mistake: there is random "grain" or visual static in every digital image, but it is more evident if you use high ISO (or gain) settings or a long exposure, because in the shooting conditions where these settings are necessary, there is a poorer ratio of image information to noise. Turning up the ISO amplifies both the information and the noise, making the noise more apparent. In the same way, recovering shadow detail in post-production seems to introduce noise, but actually it is just making visible the noise that has always been present in the image – the shadows are areas where by definition less light has reached the sensor and there is consequently less image data in proportion to noise.
So is it possible to minimise or even reduce noise in images and video shot in low light? Here's a quick guide to noise reduction technologies and options, particularly those available in-camera in Canon cameras.
"There are essentially two categories of noise," says Mike Burnhill, Senior Product Specialist at Canon Europe. "First, there's the category of noise which is created at the pre-capture stage by inherent electromagnetic phenomena – things like photon shot noise or crosstalk. At Canon, we're always trying to reduce this type of noise by redesigning sensors to help improve the signal-to-noise ratio.
"Then there's the category of noise that's generated at the digital image processing stage, which can be broken down into chrominance noise and luminance noise." These two types of noise can be tackled with noise reduction, which can be applied either in-camera or using software. Noise reduction capabilities in current Canon EOS and Cinema EOS cameras are more sophisticated than they've ever been. And the processing horsepower that you get with a computer and software such as Canon's free Digital Photo Professional (DPP) enables further noise reduction results.