Introduction to Curves

Why is the Curves tool so important?

Curves are simply another way to manipulate the histogram, however they allow more control over an image than levels alone does. If one were to stretch an image using just the Grey-Point slider in levels, the final result would look flat and devoid of much contrast. On the Contrary an image processed correctly with Curves can be contrasty and much more brilliant overall.

As with Levels there are a few Basic Rules. With a basic understanding of the Curves tool it becomes an easy to use , powerful asset for image processing.

Throughout this Tutorial i will give you the rules to using curves, and a few example curve shapes to work with.

Clipping is again Rule Number 1

Even thought we are not working with sliders in curves as we were in levels, an image can still be clipped. Clipping is easy to see with the curves tool, and thus it is easy to avoid. Simply Remember that you can not to Flat-Line the curve. This means that the top or bottom of the curve may not make contact with the edge of the curve window. Directing your attention left, i have demonstrated how you can clip the histogram using curves.

The Example on the Left has a clipped white point, while the example on the right has a clipped black point.

General Curve Shapes:

The Example Curves on the left demonstrate two ways to use curves to stretch an image.

Curve Shape Number 1 on the left is a good way to increase the brightness of the shadows without increasing the brightness of the highlights drastically. This shape is good because it will not bloat the stars, and will not brighten the cores of galaxies or nebulae too much.

The Galaxy image on top shows the result of an iteration of curve shape number 1.

Curve Shape Number 2 on the right is a good way to increase the brightness of both the shadows and highlights while achieving good contrast in the shadows.  The Galaxy image on bottom is associated with Curve Shape Number 2.

Experiment with Different curve shapes in your processing routine to see what works best for you

Curves For Contrast

The Standard for increasing contrast is the S - Curve. It works just like it sounds. Bend the Curve into an S Shape and contrast will be added to an image.

The “stronger” the S Shape the more contrast will be added. The Curve Shape on the left will add more contrast than the shape on the right.

User Defined Clicks

Understanding how to use the Photoshop tool “Curves” is just as important as understanding levels, because it is simply another method of histogram manipulation. However, Curves gives you more control of the histogram over levels. This Tutorial will teach you how to use “Curves”