HDR, or high dynamic range, photography has become so popular that the technique has become an almost universal feature in smartphone camera apps. While I’ve already discussed what HDR photography is, I will sum it up before I share it’s noise reduction qualities. HDR is the process of capturing multiple photos of the same exact image, but in varying exposures, then combined in software. Doing this allows the photographer to capture details in all ranges of light across the scene — shadows aren’t black, highlights aren’t washed out. Our eyes can see more than many cameras can capture, but HDR helps correct this.
There’s another benefit to HDR photos that many people don’t realize: noise reduction. Exposure is controlled by three aspects of a camera, one of which is responsible for how much noise or grain is visible in the photo. The aperture is the lens opening and affects how much light can enter the camera. The shutter speed is how long the image sensor or film is exposed to light — slower shutter speeds mean the sensor or film is exposed to light longer, capturing more light. Then there’s the ISO setting. The ISO is a digital representation of film speed, which is also how sensitive it is to light. It’s not a fixed value. The ISO can be adjusted to a wide range of sensitivities to accommodate the lighting conditions of any scene. The catch is that the higher the ISO is set, the more noise is produced.
How does HDR help with noise reduction? Simple! The noise produced in photos is random. When combining multiple images of the same scene, some of the noise can be canceled out. The more images captured, the less noise is visible in the end product — much like image stacking. Though keep in mind, some settings in processing your HDR photo can add more noise to the image than was originally there if you aren’t careful. Increasing the brightness in shadows too high can make noise more visible and over-saturating the image can introduce more color noise than was there originally.