Make Your Photos Better Using GIMP Levels

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How to Use GIMP Levels to Improve a Photo

GIMP offers a range of tools and features you can use to improve your digital photos. The Levels adjustment feature is an easy way to tweak a picture.

The Levels dialog in GIMP may look a little overwhelming, but it is a simple tool to use. It doesn't offer the same flexibility as Curves, but for many images, it is just as effective a tool for making the most of a photo. 

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Open the Levels Dialog

Open an image you think could be improved in GIMP, and go to Colors > Levels to open the Levels dialog. It may look a bit confusing, but making adjustments using Levels is straightforward and simply a case of dragging sliders.

The Input Levels slider is where most of the magic occurs, but the Output Levels slider can also improve the appearance of some photos.

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Adjust the Input Levels

The Input Levels shows the histogram of the image, and below it are three sliders. The one on the left is for black values or shadows, the right one for is white values or highlights, and the slider in between them is to set the mid point between black and white.

If you move the black slider across until it is level with the left edge of the histogram, you can ensure that your image contains pure black tones. Sliding the white slider right until it touches the right edge of the histogram ensure that the image contains pure white pixels. In practice though, keeping the two sliders just outside of the histogram retains detail throughout your photo, while maximizing contrast.

Moving the middle slider left lightens the image's mid-tones and moving it right darkens them.

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Adjust the Output Levels

The Input Levels slider is responsible for most of the work when improving your photos. However, the Output Levels slider can also play a part. Moving the white slider to the left reduces the value of white pixels so that in reality, the final image includes no white pixels. Moving the black slider to the right causes black pixels to become dark gray.

This effectively reduces the contrast of the image, but this can be used to counter blown out highlight areas in a photo—small areas of bright white clouds in a darker sky, for example. Dragging the white slider left make pure whites pale gray, and this can recover small areas of a photo, although if the blown-out areas are large, the image starts to look flat.