October 2 2013
The clone tool in the GIMP image manipulation program is ideal for retouching spots or removing small objects from digital photos.
The GIMP’s clone tool is often used for removing distracting objects from larger background areas such as sky and water. In the example photo the request was to remove the picture on the wall behind the subject.
Sometimes unwanted objects in the field of view are unavoidable, and other times people ask for help rescuing their compositional mistakes. In the example photo is a family snapshot with a distracting picture in the background.
The plain wall background in the example digital photo is one of the easier situations to edit with the clone tool, as the lack of detail makes blending easier. The clone tool copies image data from neighbouring sections of the wall and then blends this into the target area, using a variety of brush simulations.
One of the advantages of the clone tool is the degree of control over pasting, so the copied material is blended with the underlying content, rather than a straight pixel for pixel replacement. Selection tools, such as the magnetic lasso, are for isolating an area for adjustment or moving an object, while the clone tool is about blending an area into its surroundings.
Preserve the original
The first step is to save a version of the photo as an .XCf file; this is the GIMP’s own file format. This preserves the original photo and provides a working copy for editing. Each time you save a photo as a JPEG some of the image detail is lost. During any editing session you should regularly save the file when you complete a processing stage, so repeatedly save it as a JPEG will result in a gradual loss of quality.
Selecting the Source
In the tool dialog box users specify the size of the circular selection, and this is the same for the brush as well. There are a number of ways of doing this:
• Enter a numeric value
• Up and down arrows
• Drag the bottom half of the slider bar for small changes
• Drag the top half of the slider bar for larger changes.
There are other advanced options for the brush shape (Aspect Ratio) and angle of the brush, but for this task the standard round shape is fine.
Then move the cursor to the spot to start copying from and press the Command key and click on the spot ( CTRL – click on a PC) to confirm the source point. This location is only the starting point for the operation. The GIMP applies the clone area using a brush, and the source point moves the same distance and direction as the brush on each stroke. For each new brush stroke the clone tool starts copying from the original point.
Applying the clone
The GIMP’s clone tool simulates a paint brush for applying the copied part of the photo with different sizes, shapes, and textures. The clone tool shares the current brush shape and pattern for applying the copied material. In broad areas use a larger brush or sponge to apply the new content as a light texture when blending is important. Then there are smaller harder edged brushes for working close to neighbouring objects or lines.
Sometimes you need to completely replace an object or section, and other times just making them less obvious is a better option. What you need to avoid is an obvious trace of editing. The GIMP’s selection of brushes include some where the intensity diminishes away from the centre part of the brush, and these are good for large areas.
Another aid to avoiding harsh transitions between the edited area and the existing part of the photo is to set the opacity of the brush to less than 100. This does mean more brush strokes to cover an area, but several light strokes blend in better than one thick and heavy one, to use a painting analogy. Keeping the brush size small is another means of requiring more brush strokes and reducing any obvious transition areas between the old and new parts of the photo.
There is a slight complication in the example photo as the wall in the background is not evenly lit, so the wall gradually darkens further away from the camera. This needs to be considered when positioning the source starting point. As the application brush moves from the lighter to darker areas the source point should moves through a similar area. This may mean moving the source start point during the process.
It does take some practice to get the feel for matching the moving source with the destination when applying the clone brush strokes. A handy feature is the Command – Z keystroke combination (or CTRL-Z) to undo the last brush stroke. It is always prudent to save the working copy even when the process is only partially complete.
Close to the subject’s head there are definite lines it is advisable to zoom in and use a smaller source and brush combination to get in close. Using a brush with a more even distribution helps to cover the parts close to the head without the outer bristles straying onto the head, particularly around the ears.
Wispy hair bits are often a problem because there are so many of them and they are semi transparent, with the background visible through the hairs. Set the brush to low opacity and do the best you can while accepting that some of the subject’s hair may be lost in the process. The aim is removing any obvious barrier or transition between the head and the background.
Another problem is the harsh direct flash has created a shadow outline on the wall this is reduced by carful close cloning using the zoom and small brush approach.
To soften any transitions, the GIMP has a blur tool and brushstrokes with this tool softens the outline and smooths the shading transition on the wall.
Cropping the final version of the photo changed it to a vertical or portrait orientation cutting out more of the background distractions.