Image Noise: Why It Occurs And How to Avoid It
Your digital camera is a remarkable piece of technology, but it’s not perfect. Images it captures will be marred to a greater or lesser degree by noise. Noise is the blotches of colour or random variations in brightness that is most often seen in shadows or across even areas of tone such as sky.
Slightly ironically it’s usually the camera’s fault. Noise is caused by random signal fluctuations in a camera’s electronics corrupting the data used to create an image. The noisier an image, the more that fine detail is reduced and the coarser the image will look.
There are actually two types of digital noise: luminance and chroma. Of the two, luminance noise is arguably preferable. Luminance noise makes an image look gritty, the effect being very reminiscent of film grain (film grain is itself a type of image noise, the higher the ISO of a film the larger the grain and therefore the ‘noisier’ the image).
Chroma noise however causes the blotchiness of colour mentioned above. It’s not particularly pleasant to look at and unfortunately of the two types of noise it’s the hardest to remove successfully.
The likelihood of seeing noise in an image is affected by several factors. Increasing the ISO on your camera will make noise more prominent. If I can I’ll always use a camera’s lowest ISO setting, as this produces images with the least amount of noise.
If I use Auto ISO I prefer to restrict the range the camera chooses, avoiding the highest ISO settings altogether. Photography sometimes involves compromises however. I’d rather have a noisy image caused by the use of a high ISO than one that’s unusable because of camera shake.
If you’re shooting Jpeg you’ll be able to specify whether you want High ISO Noise Reduction (the exact wording varies between brands) applied. This generally does a good job of reducing high ISO noise, though it can sometimes be applied too aggressively by the camera, making images look too ‘plasticky’.
Sometimes the cure can be worse than the disease…Raw shooters will have to wait until postproduction to combat noise. However, this does mean that there is more control over the process. You get to choose how much or how little noise is removed.
Another factor that affects noise is the age and size of the sensor in your camera. Sensor technology constantly moves on. Each new generation of sensor improves on what’s come before. Modern cameras can shoot cleaner images at higher ISOs than cameras from even just few years ago. Unfortunately however, size matters.
Smaller sensors will always suffer from noise more than a larger sensor. I’m happy to use ISO 1600 if necessary on my full-frame camera but wouldn’t dream of going above ISO 400 on my compact camera. Experimentation is a good way to discover how good – or bad – images are at the various available ISO settings on a camera.
A third way that noise will make an appearance is when shooting long exposures. Typically this means one second or more. The longer a sensor is active, the hotter it will get. Heat also corrupts image data. The digital sensors in cameras used by astronomers to create images are often cooled using liquid helium to avoid this problem.
However, that’s a bit of a stretch for everyday use. Fortunately most consumer cameras offer a Long Exposure Noise Reduction facility. The drawback is the camera needs to shoot twice, effectively doubling the length of the original exposure.
Finally, there’s a fourth way to see noise in an image. And this time it’ll be entirely your fault. If you underexpose an image and then lighten it in postproduction you’ll increase the likelihood that noise will become visible. This happens because you’re effectively increasing the ISO.
Underexposing an image by three stops and then lightening it to the correct exposure is the same as trebling the ISO. It’s always better to correctly expose an image or even use a technique such as ‘Exposing to the Right’ described in an earlier blog.
Just over 70% of the earth’s surface is covered by water. It’s no wonder then that water holds a strong fascination as a photographic subject. However, successfully capturing the essence of water can be tricky. It has three forms: liquid, steam and ice. It also […]
No lens design is perfect. To a greater or lesser degree there will always be something that just isn’t quite right. The most common of these failings are chromatic aberration and light fall-off. Sometimes these flaws are minor and generally aren’t discernible. Sometimes however these […]
After many years as a keen amateur photographer, I decided to start a small landscape photography business called Lakescenes which I ran alongside my main job as an IT Manager. As business increased, I found myself working long, but rewarding, hours just to keep up […]
Rob Sheppard is a naturalist, nature photographer and videographer who says his favorite location is the one he is in at any time. He is the author/photographer of over 40 books, as well as a well-known speaker and workshop leader, and a Fellow with the […]
Gary Hart has photographed California’s natural beauty for over 30 years. Gary’s photos and writing have appeared in many publications, most recently Outdoor Photographer and Sierra Heritage magazines. You’ll also find his images in greeting cards, postcards, calendars, and many galleries and private collections throughout the world.
Originally from Poland, based in London UK, Jaroslav has background in Fine Arts, degree in Architecture, and wide array of experience. Being an Architect taught him how to be resourceful and to solve complex problems with simple, yet innovative solutions. Constant passion for graphic & […]
Next time you’re in the countryside at night do yourself a favour: look up. If it’s clear and conditions are right you’ll see a seemingly infinite number of stars twinkling like diamonds on a sheet of black velvet. As a visual pleasure it’s hard to […]
Contrast is usually at its highest when a scene is backlit. In this image there wasn’t much that could be done to lighten the shadows. I exposed so that the highlights weren’t too badly burnt out and didn’t worry too much about the shadows. Contrast […]
Colour can be distracting. Stripped of colour an image is entirely about the subject (unless of course the entire point of the subject is its colour…). This is particularly true of portraiture. Black and white arguably conveys the inner soul of the subject more powerfully […]