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Archives: Removing digital noise from images
What is digital noise?
Digital noise can be described as the unwanted effect of your camera’s sensor when it records colours on your image incorrectly. It is the digital equivalent of film grain in analogue photography. In those golden days, the different photographic films would be designed to react to light at a different speed and you would choose your film’s ISO (originally ASA Value) value depending on your needs.
- 100ISO – Studio photography under Powerful lighting
- 200ISO – Outdoor in bright sunlight
- 400ISO – Outdoor on cloudy or overcast days
- 800ISO – Outdoor when Raining or indoors
- 1600ISO – Sports and Track.
As the speed of the film increased, so did the grain. But, even at 1600ISO people were that used to seeing a little grain, that it was just ignored. Some people even liked the look of the grain on their images.
On a digital camera, we use the same notation with sensor speed. However, there is a general desire, and it’s not shared by everyone, to make absolutely crystal clear pin-sharp images. Noise has become the public enemy no.1.
What Causes Noise?
Let’s take a look at the main causes of noise.
- Salt And Pepper Noise (impulse noise), is noise spikes that can be caused by errors from the Analogue to Digital convertor. These days as cameras have improved it’s less and less apparent.
- Shot Noise is the dominant noise which effects images. If you think that when a colour is being recorded at one point on the image sensor, an average of the intensity of that light is calculated at that point on the sensor for the duration of the exposure is calculated by the camera’s processor. But, the shorter the exposure, the fewer values the camera has available to make the average calculation from. The values themselves are not just affected by the light, but as an electronic device, a camera’s power will be fluctuating fractionally as it’s operating. these fluctuations affect the data coming from the sensor. So it becomes less accurate with the faster shutter speeds.
It’s also said that another cause of digital noise can come from the image sensor getting warm and producing errors on the image. But, as someone who takes very long night time exposures, I personally haven’t encountered the problem.
How can you reduce Noise when shooting.
As I mentioned above salt and pepper noise has become less and less apparent as cameras have become more developed. But, for more general shot noise, the best option appears to be, ‘always buy the newest camera’. The more modern processor, the faster it will work and thus the more accurate the average calculation for each sensor location will become. Indeed, camera manufacturers are tirelessly working on faster and less noisy sensors. If you are looking into becoming a wedding photographer, shooting in dark churches and venues, or a music photographer, then the more professional camera, with the newest processor is going to be a less noisy advantage. But, if you are not, or don’t want to upgrade your camera, then you must remember the golden rule of always shoot with the lowest ISO that you can and that can also be helped by shooting as wide open in your lens as possible, f/2.8 or even on a f/1.8 or f/1.4 prime lens if you have them (or rent a higher grade camera).
How to deal with noise on your images.
And so we come to the inevitable final part, you don’t want to change your camera for the one time you have to shoot a concert (rent one instead), and your lenses are as fast as there going to be. What can you do about the noise on your images?
For many photographers, Adobe products have become an essential part of their workflow, other solutions exist for sorting and processing images, and many carry noise removal options. Unfortunately, I don’t use Adobe products, instead, I use Corel Aftershot Pro for organising and Paintshop pro for editing my images.
The following images were shot at 6400ISO on a Canon 70D at f/2.8 and 1/200th seconds.
With Aftershot pro, you have the Perfectly clear Noise removal option, it works quite well and for mild noise does a good job. But for a few more options we look at what Corel Paintshop pro can do.
With Corel’s Paintshop Pro, you have a ‘One-Step Noise Removal Tool’, one simple click on from the menu and all the hard work is done for you. It’s not a bad result if you don’t want to over-edit the images. You can see the effect of noise removal in the slight blurring of the image, often therefore further processing will be needed to sharpen the image again.
If you like to be more hands-on then the Digital Noise Removal Tool will allow you to alter the prominence of either small pixels, medium size pixels or large pixels, this allows you to have more control over which areas you adjust and can be used to reduce the amount of blurring that occurs as part of the noise removal process.
The digital raw removal tool in Paintshop pro is essentially a cut-down version of the Topaz labs Detail Plugin. Topaz gives you a whole host of bells and whistles, as well as many presets. You can spend a lot of time adjusting the noise and can adjust large medium and small pixels as well as adjusting the highlight and shadow areas separately.
But the issue with all these solutions is that they are a fix-all solution. That is to say, they don’t know or even care what camera the image came from and rely on the skill of the user to judge when each slider is set in the right place or are just an algorithm to cover all noise in one go. But, there is another option.
Don’t forget about the software that comes with your camera.
You may, like many of us do, think that you know your cameras better than anyone else. Well, I’m sorry but the camera manufacturer has to be considered the number one expert when it comes to your camera. They built the camera, they built the sensor, so nobody is going to understand the noise from the sensor better than the people who made it. And they even provide you with in-camera noise reduction software as well as applications for your computer.
The in-camera software provides processing which helps produce jpegs straight out of the camera. Do you remember that your camera can make jpegs? Well, your camera will have noise reduction settings, which if you shoot in Jpeg will be transferred to the final image, making them cleaner straight out the camera. However, when the RAW files are exported to your computer, they contain the sensor data and data about the camera settings. Third-party programs such as lightroom, after shot Photoshop or PaintShop Pro, ignore this information completely. They just don’t know what to do with the camera’s noise reduction setting and as there are so many different cameras, a fix-all noise solution rather than a camera-specific solution is going to be employed.
If you are shooting in a low light High ISO situation your best option would be to import and initially process the images using the software that came with the camera. That software is going to be specifically designed for your sensor and is not a fix-all algorithm. The last 2 pictures of this article show the difference between the image processed through the Camera’s own software (top) and the raw file (bottom). Certainly even at 6400ISO my trusty Canon 70D can still make a reasonable image when processed the right way.