Using GIMP: Correcting and Touching Up Your Images - GIMP 2.6 for Photographers: Image Editing with Open Source Software - page 116

2.5.7 Using the Gaussian Blur Filter
to Remove the Moiré Efect

Next, you'll want to remove the moiré effect from the image. For this action,
you will use a filter called Gaussian Blur ( Filters > Blur > Gaussian Blur ) .

Figure 2.44
The Gaussian Blur window.

After selecting the Gaussian Blur filter, use the dialog to set the amount of
blur desired. A higher value will produce more blur.
The filter can also be used to blur the background of an image. If you
paste a sharply drawn object in the foreground, it will seem even clearer in
contrast to the blurred background because the image gains more depth.
However, since in this case you are concerned only with correcting the
moiré effect, the image should retain most of its contour sharpness.
In the Gaussian Blur dialog, select the RLE option. (RLE stands for run-
length encoding, an algorithm for lossless data compression. Repeating
values are replaced by specifying a value and a counter.)
Enter a value between 3 pixels and 5 pixels in each of the two Blur Radius
fields. In this example, I entered 5. You can select non-integer values by typing
them in the fields. Remember to use the comma instead of the decimal point.
The Gaussian Blur dialog provides a preview with an image section so
that you can see the effect of your settings. Click on the image with your left
mouse button to view the original image. Let go to see the filtered image.
In the bottom-right corner of the preview pane, you see a double arrow.

• NOTE
As a rule, most filters should be used
after you've finished with all other
image editing work. Remember to
save a copy of the image before
using a filter. However, the Gaussian
Blur filter is an exception if you are
using it to remove the moiré effect.