Using GIMP: Correcting and Touching Up Your Images - GIMP 2.6 for Photographers: Image Editing with Open Source Software - page 140

2.7 Touchup Work 2—Removing
Spots, Dust, and Scratches
Older images or slides often have blemishes, such as creases, dog-ears, spots,
dust, scratches, and missing edges. Also when you scan slides, lint and dust
often end up on the image. Even digital images can have disturbing elements
that need retouching, such as overhead wiring in the picture or dust on the
camera chip. The touchup work involved to fix such images is called constructive
touchup since it involves “reconstructing” image elements. Constructive
touchups also include removing image elements, such as unwanted text.
Formerly, photographers armed themselves with brushes, maskers, and
airbrushes when fixing damaged images. Nowadays, images are scanned
“as is” and the photographer's repair tools are supplied by the image editing
program. But the techniques are similar, the main difference being that the
tools are now in digital form. It seems as if every new version of a digital
editing program introduces new tools for correction and stylization of images.
2.7.1 Why You Need Smooth
Brushes—the Clone Tool
The Clone Tool uses image data and patterns to “draw” not only colors, but also
color structures. These structures are actually pieces of your image that you
previously copied from a defined area in the same image. This tool is capable
of doing more than just working with “normal” opacity. Since you can set the
tool's opacity from opaque to transparent, you can use this glazing technique
to create smooth transitions, using a soft, feathered pointer. The Clone Tool is
considered “the” touchup tool.
The Clone Tool uses the same brush pointers available to the drawing
tools. Choosing Windows > Dockable Dialogs > Brushes , you will find brush
pointers with hard, sharp edges that draw like pens with fixed widths as well
as pointers with soft edges or feathering that draw more like a paint brush,
with rich color in the center that fades as it moves toward the edges. Moreover,
there are brush pointers in the form of patterns that apply color in structures.
For this exercise, you will use the Clone Tool with “soft” pointers. Brushes
with hard edges will create image patterns with sharp edges: this may be
acceptable for a single color, but if you are working with structures, even
similar structures, the image would appear as if it had been strewn with
confetti. A softer brush pointer creates a smooth transition.
Because GIMP doesn't come with a large array of brushes, it provides
a simple way to create new brushes. You should create a certain choice of
additional brush pointers in advance so that you can change a pointer quickly
when you're working. Once you have created a brush, you can save and reuse it.