The Color > Curves effect

Each pixel on the screen is defined by its components:
* The so-called RGBA generates the color of a pixel with four components: red, green, blue and alpha. In this system, the values of the four components vary between 0 and 255.
* The HSLO system generates the color of a pixel using four other components: hue, saturation, luminosity, opacity. In this system, the values of saturation and luminosity may vary between 0 and 255, the hue may have a value between 0 and 359 (thus the previously used concepts of angle and color wheel).

Inversely, any pixel on the screen may be broken down in each of the two coordinate systems. Modifying the color of a pixel therefore means you modify the values of its components.

The Curves effect enables precise management of these modifications: the Mode popup menu offers a choice between the two systems described above.

Let's go, for example, into the RGBA system and take a look at our image. Next to the name of each component we find a miniature profile, comparable to those we encountered when studying the drawing tools and acceleration of an effect.

Click on the Red miniature profile to call up the edit profile window.

The options proposed are traditional: flip the curve along the "X" or "Y" axes, use pre-defined curves, save the settings, modify interpolation of the points…

Now we just have to study the meaning of the curve:
* The horizontal axis represents all luminosity values that may be contained in a pixel on the screen (values between 0 and 255)
* The vertical axis (also known as LUT : Look Up Table) represents all luminosity values of the pixels once the Curve effect has been applied.

Let's take the curves below as examples:

* In the first example: the luminosity of every pixel is divided by two after application of the effect (for example, a luminosity value of 50 changes to 25 after application of the effect).

* In the second example, the luminosity of every pixel remains unchanged.

* In the last example, any pixel with a luminosity value between approximately 64 and 192 will turn black, the others remain unchanged.

We have just studied the luminosity curve in detail. Now it's up to you to work with the other curves and use them to the advantage of your projects.