Gimp tutorial: noise reduction with G'MIC

Tutorial for high ISO digital noise reduction with Gimp's plugin G'MIC.

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Gimp doesn't provide a good filter for digital noise reduction, fortunately there is G'MIC. It is a free plugin for Gimp, with over 500 filters. Among them, there are three that are used to remove digital noise from photographs taken with a high ISO values. These three noise reduction filters are called Smooth [Anisotropic], Smooth [Thin brush] and PhotoComix Smoothing and we'll go to describe them in this tutorial, but first let's see what digital noise is. If you are not interested, you can skip the next chapter by clicking here.

Gmic setting

What is digital noise?

In digital photography the noise is given by the electric current passing through the sensor. Normally it isn't possible to notice it, because with a good light condition the camera sensor works well. In low light, however, the camera has to counterbalance the lack of light, increasing ISO sensitivity. This process leads to a strong amplification of the electronic signal recorded by the sensor and this amplification creates an increase in digital noise, which results is an image that looks "grainy", which is very annoying.

Generally, in the small preview shown on the camera's display, the digital noise is not even noticeable, but once the photograph is analyzed on a large screen, such as a computer screen, the noise becomes noticeable and makes a photo that at first glance seemed perfect look worse.
Below you can see two 100% crops of the image I used for this tutorial. This is a set of colored felt-tip pen, and the light source is a feeble light bulb. The first example was taken at 3.200 ISO, the second at 12.800 ISO with a Canon 5D Mark II camera, a full frame with some years on her back. Obviously no noise correction has been applied in the photos. No changes has been made to the file, not even a white balance, which has been set to automatic.

3200 iso
5D Mk II 105mm f/6.3 1/30 sec. ISO-3200
12800 iso
5D Mk II 105mm f/6.3 1/125 sec. ISO-12800
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Install G'MIC

Unfortunately it is impossible to remove digital noise with Gimp alone. Fortunately it is possible to increase the features of Gimp installing a "Plugin". G'MIC is one of these plugins, a program that expands the functionality offered by Gimp. You can download G'MIC directly from their website at the address http://gmic.eu/download.shtml.

We recommend to download the installer if you use Windows, taking care to choose the correct one for the version of Gimp you have installed. To find out which version of Gimp you are using, open the Help → About Gimp menu. Then remember to close Gimp before installing G'MIC. Once you have downloaded the installer, simply open it and install it in the absolutely traditional way, by pressing a couple of times the button Next.
After the installation of G'MIC open Gimp, then go on the menu Filters and verify that G'MIC-Qt... has appeared inside the menu.

Gmic Setting

If the button is grayed out, you just have to open a photograph to activate it. The loading may be a bit slow the first time, in that case you need a little of patience. You'll notice that this plugin has a huge list of effects, there are over 500 filters available, and it includes a number of funny or interesting functions to explore. In this tutorial we are going to see only noise reduction, but we suggest you to take a look at the various effects available.

The interface of G'MIC is quite simple:

Gmic interface
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As we said, the G'MIC filters we're going to explain are three:

You can search them in theyr groups, but the fastest way to find them is to use the search bar. You can also click on them with the Right mouse button → Add fave to find them always in the first section, named Faves. Let's see in detail their functionality and the differences that distinguish them in noise reduction. For those who want to make a more in-depth testing, next you can download our test files, that are available in full resolution.

Remember that you should always use your photos to perform a tests, because ours have been compressed.

The test

For each filter there will be three images: the first is the ideal photograph, taken at 100 ISO. The second is the photo at 3,200ISO with the corresponding noise reduction applied. The third is the photo at 12,800ISO with the reduction applied. Since the crop is rather small, there will also be links to download the images in high resolution, obviously with noise reduction applied. It's not easy to compare them because of the distance, so after the explanations we'll put them next to each other for a better comparison.

Sample file at 100 ISOExample file at 3200 ISOSample file at 12,800 ISO

Noise reduction with G'MIC's Smooth [Anisotropic] filter

The first noise reduction tool for G'MIC that we are going to describe is the filter Repair → Smooth [Anisotropic].
With the standard parameters you can already get some excellent results, but increasing the Amplitude to 100 and reducing the Anisotropy to 0.2 gives even better results. On the 12,800ISO photograph it was necessary to raise the value of Amplitude to 400. If you mess up the various parameters while trying different settings, you can go back to the initial conditions by clicking on the upper right arrow.

anisotropic settings

If you want you can see the photos in original resolution with the Smooth [Anisotropic] filter applied with the default parameters: here you find the file at 3,200 ISO and here the file at 12,800 ISO. Below you can see a detail, at 100% zoom, with our suggested parameters applied.

Sample file at 100 ISOanisotropic 3200 ISOanisotropic 12,800 ISO

Noise reduction with G'MIC's Smooth [Thin brush] filter

The filter Repair → Smooth [Thin brush], in theory, would keep the image sharper, but tends to create a "brushstrokes" efect that I don't like at all. To counter this issue we had to lower the Sharpness, but the lost of detail could be too much. It is necessary to balance, according to your personal taste, two parameters: Amplitude, which we have raised to 100, and Sharpness, which we have lowered to 0.5 for both ISO values.

Smooth Thin brush settings

The results are not bad at all, keep a lower sharpness helps to hide the "brushstroke" effect. This tool for digital noise reduction with G'MIC is really good.
If you prefer to see the photos in original resolution, with the Smooth [Thin brush] filter applied with the default parameters here you find the file at 3,200 ISO and here the file at 12,800 ISO. Below you can see a detail of the result at 100% zoom, with the parameters recommended above applied.

Sample file at 100 ISOSmooth Thin brush 3200 ISOSmooth Thin brush 12,800 ISO

Noise reduction with G'MIC's PhotoComiX Smoothing filter

The most "aggressive" filter can be found on Testing → PhotoComix → PhotoComiX Smoothing. It reduces the image sharpness more than the other two, but is particularly effective for photos with a lot of noise. We recommend to set the value Amplitude to 100 and change the Sharpness according to the noise. We used 0.4 for the photo at 3,200ISO and 0.2 on the photo at 12,800ISO.

PhotoComiX Smoothing settings.

If you want to see the result in high resolution with the filter at the default parameters you can download here the file to 3,200 ISO and here the file at 12,800 ISO. Below you can see a detail of the result at 100% zoom, with the parameters recommended above applied.

Sample file at 100 ISOPhotoComiX Smoothing 3200 ISOPhotoComiX Smoothing 12.800 ISO

Comparison at 3,200ISO

For an easier comparison below you can see, side by side, the three filters with the recommended settings. At 3,200 ISO the result is similar and good with all the three filters: the winners, in my opinion, are Smooth [Anisotropic] for the sharpness and Smooth [Thin brush] for the best noise reduction.

anisotropicSmooth Thin brushPhotoComiX Smoothing

Comparison at 12,800ISO

Also for ISO 12,800 you can see below the results side by side with the recommended settings. In this case the work required for the noise reduction was more complex. I think that Smooth [Thin brush] gives better results, but the loss of details is huge.

anisotropicSmooth Thin brushPhotoComiX Smoothing
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Now you should do your own tests, applying what we have learned about noise reduction from photographs with G'MIC, but first we would like to give you some advice, in general, for all the filters we have seen:

Paying programs

The results that can be achieved with G'MIC are good, but are not comparable to those that can be achieved with paid solutions. With a lot of work it would be possible to achieve a noise reduction at the same level, in fact these programs use very advanced algorithms to divide the image into several zones, and apply different parameters to different parts of the photo. I also think that they apply contrast masks where they find sharp lines and more soft parameters where there are strong blurs or gradients. By dedicating the right amount of time to editing (sometimes a lot) I am sure that it is possible to obtain similar results, if not equal. Having all this automatically applied, with a few clicks, has a cost.
When we started experimenting with astrophotography we decided to buy a license of Topaz Denoise, probably the best professional solution available today. Obviously it is compatible with Gimp, using a plugin called PSPI. Needless to say, the results are better than what we can get with G'MIC, at least if we don't want to spend a lot of time on it. If you want to see the result in high resolution you can click here for the 3,200 ISO file processed with Topaz denoise and here the file at 12,800 ISO, also this processed with Topaz. Below you can see a detail of the result at 100% zoom, with the default parameters applied.

Sample file at 3200 ISO
Original 3200 ISO file
Smooth Anisotropic Filter
Topaz DeNoise 5

Final touches

To try to counteract the loss of detail given by noise reduction. it is possible to increase the sharpness of the photograph, here you can read a tutorial on how to do it.

Of all the other filters available in G'MIC-Qt we'll talk soon in another tutorial, but I suggest you to spend some time exploring all the available effects, because you can find really interesting artistic solutions.

If you liked this tutorial here you can find all the guides we have written about gimp, from the simplest to the most advanced, or you can all the guides we have written about photography in general. If you liked our work, you could consider to support us: by clicking here you can see how.

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