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Enhancing Photo Images with GIMP

 Video of how to enhance photos using GIMP

Introduction to Photo Enhancement

Even the best photographers cannot always take the perfect shot directly with their camera. Sometimes lighting conditions are far from ideal (-for example, high contrast) or there are objects in the way such as signposts that detract from the composition. In these cases, the solution is to use a graphics package, such as GIMP to perform some image manipulation to enhance the final solution.

Note: you can view a demonstration of how to enhance photos with GIMP in our Video Section

Adjusting Levels in GIMP

One of the most common challenges for photographers is contrast and lighting. Unless you are shooting in a controlled environment, such as a studio, it is sometimes not possible to find an exposure to cope optimally with both highlights and shadows; for example, strong sunshine tends both to bleach out highlights and create strong shadows. In these conditions, the only way around this is to use post-processing tools to manipulate the image(s) after the fact.

If the difference between highlight and shadow is not too great, the image can be manipulated fairly easily using GIMPs "Levels dialogue using:

Colors → Levels

GIMP Levels Option

A dialogue box will open up showing a graph with three small triangular sliders underneath, which can be moved up and down. These represent:

  • On the left hand side, is the slider for shadows: make sure this is moved up to the the start of the first peak in the graph (-as shown)

  • In the middle, is the slider for midtones: move this up or down until the preview shows the ideal amount of detail (-normally around halfway between the two other sliders)

  • On the right hand side, is the slider for highlights: make sure this is moved down to the the end of the last peak in the graph (-as shown)

GIMP Levels Dialogue

Once the preview looks optimal, with no highlights blown out or deep shadow where detail is lost, click "OK" to apply the settings to the photo in the main window.

Note: if the difference between highlight and shadow is extreme, probably the best way to deal with this is to use Layer Masks to blend multiple images together

Correcting Dust Spots in GIMP

It sometimes happens that, especially when shooting outdoors, dust can get onto your lens or even (-if you are changing lenses in a windy environment) onto your CMOS sensor. Whilst the correct solution is to clean off the offending particle, most of us don't realise the problem until we come to examine the images at home.

Like, Adobe Photoshop, GIMP gives us the equivalent of the former's spot healing brush to remove a spot caused by dust on the lens or sensor. Simply select the"Healing Tool" from the palette window on the left hand side:

GIMP Levels Dialogue

Use the "Scale" slider to adjust the brush so it is just large enough to cover the spot, then CTRL+left-click on an area of the photo close to the spot and which looks similar to the way the spot area should really look. GIMP will highlight the selected area in a circle with a cross-hair in the middle:

GIMP Levels Dialogue

Having set the source for the healing tool, simply left-click over the spot; the spot will be blended into the photo using the image set from the source area:

GIMP Levels Dialogue

Sharpening Images in GIMP

Sometimes the lighting, sloppy focusing or a poor lens can lead to a very soft image. Whilst this cannot be corrected totally if way off, it is possible to lift a slightly soft image using the GIMP "Unsharp Mask" facility. Once again, this device will be very familiar to Adobe Photoshop users both in features and in use. It can be selected from:

Filters → Enhance → Unsharp Mask...

GIMP Levels Dialogue

A dialogue box will display, showing a preview window and three sliders. First, use the scrollbars to adjust the preview window to view the area of detail you wish to sharpen (-something with vertical and horizontal lines is best - like the inscription in the photo below). Once you are previewing a representative sample, adjust the sliders below until the preview looks sharp, but not over-contrasty (-tip: don't try to overdo the effect: be subtle!):

GIMP Levels Dialogue

Once you are happy with the preview, click "OK" to apply the effect to the whole photo.

Note: any effect applied can be reversed using the CTRL+Z key combination (-or the "Edit → Undo" menu option)

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