This GIMP (GNU) tutorial explains how to remove grain (noise) from photographs using GIMP’s Selective Blur Filter. To work along, you are welcome to download (Whitely Bay’s St Mary’s Lighthouse), Here. Unzip the file and open the image onto GIMP’s workspace.
Grain (also known as noise), can be a result of several different conditions, including optical (and manual) zoom, and high speed film - and is more noticeable with blue sky, or sea. Removing grain from photographs is not a precise science, individual photographs have different needs and require different filters and settings.
You can quickly Undo a step at any time by pressing Ctrl then Z. Alternatively, click a previous Undo History snapshot - Windows then Dockable Dialogues then click Undo History. In addition, to Zoom in (or Zoom out) of your image; from the top menu choose View then select a Zoom Tool from the subsequent drop-down list.
Launch GIMP & Organise Its Workspace & Palettes
Open your choice of Start Image onto GIMP’s workspace - File then Open - Ctrl then O.
Duplicate Your Image
It’s important to preserve your original image: therefore, Duplicate your image; Ctrl then D - (Image then Duplicate). Now, close the original image, and work on the Duplicated image.
Ensure the Layers and the Undo History Palettes are visible, and then drag them into position over your workspace - (Windows then Dockable Dialogues - then click Layers and Undo History).
Selective Blur Notes
Contrary to the other Blur Filters, the Selective Gaussian Blur Filter doesn't act on all pixels: blur is applied only if the difference between its value and the value of the surrounding pixels is less than a defined Delta value. So, contrasts are preserved because difference is high on contrast limits. It is used to blur a background so that the foreground subject will stand out better. This add a sense of depth to the image with only a single operation.
Free Select Tool
If you prefer, isolate just the grainy area, (for example the sky), with a Selection Marquee using the Free Select Tool. Then apply the Selective Gaussian Blur Filter to just the isolated area.
From the top menu, choose Filters then choose Blur and then choose Selective Gaussian Blur. Now, from the subsequent Selective Gaussian Blur dialogue box, enter the following settings, or experiment, and then click OK.
To remove grain from smaller areas, from the left-side Toolbox, activate the Smudge Tool.
Now, enter the following settings into the Options Box.
Then left-click and being very careful not to overdo it, gently remove (blur) stubborn areas of noise (grain).
Congratulations, you have successfully removed your photograph’s grain (noise), and your work is ready to save.
Wendi E. M. Scarth. Top of Page.