How to Reduce Noise From a Photo

In this tutorial you can learn how to reduce noise from a photo with the help of several photos of the same subject.

What is noise?

Noise is a problem in digital (but also in film) photography as it consists in artifacts as reduces image's quality. Noisy images have lots of pixels with color "errors". Pixels affected by noise are different in color from the subject they are representing. This color shift may be moderated (In this case the color is similar to the others in that particular part of the image, but stronger or weaker) or more extreme (In this case we have color noise: lots of pixels are blue, red and green regardless of that part's color).

What increases noise?

Digital cameras has a sensor with different light sensitivity capacity. This capacity is measured in ISO. More ISO means more sensitivity and more light. Increasing ISO, photos presents more artifacts, noise. The best way to reduce noise in a photo is to shoot with the lower ISO possible. In cameras with manual mode you can set shutter speed, aperture and ISO. Choose the right shutter speed and aperture for the need of your shot and then set the ISO to the lower possible reaching the right exposure.

How to reduce noise?

The are several ways to reduce noise in post production:

• Using a single shot edited with a software like Lightroom (increasing luminance and color in "noise reduction" section in Develop tab)
• Using multiple shots combined and edited with photoshop (in this article we will use this type of treatment)

The method

This is the second method mentioned in the previous paragraph. The method consists of taking several shots of the same subject in the same position, with the same composition and then combining them in a single shot reducing noise.

The first thing to do is to mount the tripod and the set the camera on it. The tripod is required as we are going to shoot multiple photos of the same subject in the same position in the image. We also need a remote with multi-shots and interval capabilities. You can set the camera in the mode you prefer: manual but also auto (or others). If your camera allows to use mirror lock up, set it (but remember, if you set the mirror lock up you have to set the intervalometer with double number of the shots you decide to shoot because every two shots, one is for locking up the mirror and the second for the shutter release).

Now you have to shoot x photos of the same subject, x identical photos. You can shoot many images as you want. The best x number is between 10 and 15, but you can also shoot only 3 photos.

IMPORTANT: the subject must not move or should move coherently with the background.

I took 15 photos on the tripod using the mirror lock up, the remote with 3 second delay between the mirror lock up and the shutter release to make the shot even sharper. I have used the max ISO possible on my camera (Canon 6D), 102400 ISO (which is the H2). I have used the max ISO only to demonstrate the benefits from this noise reduction process (in real world you should use the lower ISO possible).

The result is an image very noisy, as expected (remember the shot was taken at 104200 ISO). The photo published above is one the the 15 taken in the process and it's unedited.

The real post production process has to be done in photoshop, but I am used to open images first in lightroom and then, from there, open them in photoshop. But remember lightroom applies a noise reduction by default. You have to remove that setting: go to the Develop tab and than down to the Noise Reduction section, set luminance and color to 0 (second image above). Apply this setting to all images (select the edited one and then the others with the shift button, click synth, select noise reduction if not selected, click synchronise).

Now you have to open all images in photoshop, as layers. Select all images, right click, click edit in, click Open as Layers in Photoshop.

Select all layers (click the first layer, shift + click the last layer)[Image 1], click Edit (in the top menu), click Auto-Align Layers [Image 2], click ok [Image 3]. Because of miss alignment in shooting process you have to crop some transparent pixels in the image border, use the crop tool for that.

With all layers selected right click on layers and then click Convert to Smart Object [Image 1]. Now you will see only a layer (not a layer, a smart object) in the layer list [Image 2].

In the previous step the photos were stacked one on the other. Now you have to choose the stack mode, the way the final image is composed from the stacked ones. Click Stack (in the top menu), Smart Object, Stack Mode, click Median.

The left image is the original one (the noisy one) and the right one is the edited one.

Image 2: 50% (1:2)

Image 3: 100% (1:1)

Image 4: 200% (2:1)

I have taken for this purpose other images with lower ISO (51200, 25600, 12800, 6400, 3200, 1600, 800, 400, 200, 100). I have compared the edited image (shot with 102400 ISO and then stacked with other 14 images) with the images shot with lower ISO.

The edited image could be compared with the 12800 ISO original image (ignoring some color noise) [Image 1]. Reducing color noise in the edited image (in lightroom), the edited one is better than the 12800 ISO original image [Image 2] (reducing color noise in the 12800 ISO original image, it loses contrast and some color details, so I have decided to apply color noise reduction only to the edited one and not to the 12800 ISO original one).

Left image: Edited version (102400 ISO)

Right image: Original version (12800 ISO)

We can conclude that this process can produce images with the same quality (in term of noise) of photos with 3 stops ISO less then the 15 images (combined in one). I think this is an incredible outcome, especially considering this is a process completely done by software.

This is the same process described in this article.