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Curves tool, Gimp tutorial

Curves are essential for exposure and contrast correction with Gimp.

Italian Web master: Bad English, but good tutorials.

The correction of the curves is one of the things less intuitive (but more important) as concerns the improvement of a photo with Gimp.
We have discussed previously about contrast adjustment and exposure correction using levels.
Gimp curves tool allow us to better accommodate all of these parameters with a single step. The tool is powerful, but must be used with a minimum of knowledge for optimal results.

I personally do not use curves to do everything. It's right to say that the curves allow the maximum control, but i use that only for light, if i need to modify the colors, i prefer to use the color balance.
You can find the curves tool from Colors - Curves, open it and try to familiarize yourself a bit.
Once you open the curves of the image, you will notice a line that cuts diagonally across a histogram of our photography.

curves tool

As you can see I added some red words, in order to clarify what is the specific use of the various parts of the line.
Bottom left you'll find the shadows, the lights at the top right, and at the center you can find the mid tones.
Any adjustment can be done by a simple "click and move" in the specific part of the curve that you want to edit.
There is another important thing to say, if you click any zone of the source image with the curves tool selected, you can see exactly where that zone is placed (a line will appear in the histogram).

The following example is a typical Contrast Enhancement Curve, in this case I've also cut off a little bit at the start and at the end, this is not necessary if you have already adjust the histogram:

Contrast enhancement
Continues after the advertising...

Curves are even the best solution if you need to lighten the shadows of an image: if you need this kind of result you must proceed by setting a curve like the following one:

lighten dark areas

Obviously you can also darken light zones and reduce contrast if you setup a curve like the following one:

reduce contrast curve

Remember that it is nearly impossible to get the same results of the photos in this page using only contrast or levels, so I suggest you to practice with the curves paying a lot of attention, in fact the results are great.

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