Noise reduction with G'Mic
G'Mic will help you to reduce noise on your photos with great results.
Have you ever noticed a disturb in your photos? That is noise, and can be reduced with Gimp and the great G'mic plugin
(exists also as standalone). In digital photography, noise
is generated by the electric current passing through the sensor. In a
low-light scene, the camera tries to balance the low light, increasing
sensitivity (ISO). This process generate noise that appear like a grain.
The preview that you can see in the display of your camera is too small to give you an idea of the loss of quality, when you view the photo in your computer you can have a bad surprise.
Canon 550D - High ISO noise - Crop 50%
If you need to solve this problem, you can try a Gimp plugin that is pretty good in noise reduction, its name is G'Mic.
Click here to go to G'mic download page.
The installation is a traditional windows install shield, simply double-click the executable and follow on screen instructions, but remember:
Close Gimp before proceed installation.
After installation, run Gimp normally then open Filters - G'Mic. I suggest you to try all the effects, some are really good.
On the left you can see a real-time preview of the effect you choose, in the center there is a list of all available filters, on the right you can see various customizable parameters.
In this tutorial I will write about only three effects, that you can find in the Presets section of G'mic:
- Anisotropic Smoothing;
- Thin Brush Smoothing.
Anisotropic Smoothing is the best solution for pure noise reduction, it can be found under Enhancement and will give you the lower loss of details, and last but not least is really easy to setup. Let's see a screenshot:
As you can see there are many parameters, but I suggest you to edit only the two highlighted (sharpness and anisotropy).
Generally you should have really good results with default values, if you need more sharpness, change the value from 0.70 to 0.90.
PhotoComix Smooting works quite well, the result is very clean but it produces smooth images.
Generally I change only a couple of parameters:
- Amplitude: Is the "size of the brush", generally I set a value from 20 to 80.
- Shapness: Modify the shapness of the effect, if you set a too high value, you will invalidate the noise reduction. Generally I set a value from 15 to 30.
After I used the PhotoComix Smoothing, I apply an Unsharp Mask, for counter the loss of sharpness.
Thin Brush Smooting is more sharpen than PhotoComix, but generates some bad "brush strokes", especially in the blur of the out of focus areas. The only parameter that I edit is the Sharpness, and generally I set a value from 0.5 to 0.9.
Below you can see a comparison between the two filters, that will let you analyze in detail the differences between PhotoComiX and Thin Brush Smoothing of G'Mic. This is a 100% Crop. I think that PhotoComiX is better, even if there is a loss of sharpness.
There are a couple of things to know before try to reduce noise with G'Mic:
- The processing times are long, even 15-20 minutes with 18-megapixel images (the computer is still usable).
- Don't modify Interations, results are better but the processing time become really long.
- Your photo will lose sharpness, but I think that a smooth photo is better than a noisy one. You can Apply Unsharp Mask, or even duplicate the layer and merge it with 50% of opacity.
- G'Mic doesn't does miracles: If you set insane ISO, or if you have a really noisy HDR photo, the noise will be too much, and will be impossible remove it.
Each sample of this page is really zoomed, this is the original picture with the noise reduction applied.