Bair Art Edition's Tutorial on:
Adjusting Color & Exposure
In Adobe Photoshop


Solving Exposure Problems: Using Curves


The Curves tool is a powerful way to redefine the tonal values of an image, but is not available in Photoshop Elements. The Curves tool can be found under the menu Image/ Adjustments/ Curves.

We will be using this same tool, but, of course, applying it as an adjustment layer. Adjustment layers are always preferred (learn more about ajustment layers).


Either go under Layer/ New Adjustment Layer/ Curves



Or on the layers palette (accessable in Window/ Layers) click on the half white & Black circle and choose "Curves"



A Graph will show up with a diagonal line through it. To the bottom and left of the graph is a gray-scale going from white to black. This scale can be reversed so it goes from black to white by clicking on the reverse arrows on the bottom scale. This change does not change your adjustments in curves, it only changes the orientation of the graph.



In the above image you see the curves tool. If your background grid has less of a grid to it than mine does, then you can option-click (atl-click for PC users) on the grid, and it will have more lines.

You can see that I have put an anchor point in the very middle, at the mid=point value of 128. in the lower left-hand corner there are two boxes which define that anchor point. Righ now, it tells us that we are affecting the value of 128 (Input), and that we want that value to be changed to 128 (Output). Obviously that means there is no change, but we'll see the effects in a minute when we do make a change.



Correcting Exposure

We will be lightening up this image:



Once you have brought up the curves tool, select somewhere in the middle of the line, and pull the line up or down. In this case we pulled the line up:



As you can see, the beauty of curves is that is is non-linear. Instead it makes, . . . well a curve of course. The point where I have made my anchor has been changed from the lower value of 107, to the brighter value of 149. This considerably lightens the image at this value, and that is where the farthest bend of the curve exists. From that point, the adjustment curves back towards the pure black and white values (located in the two corners). Thus the adjustmnet steadily losses it's effect as it gets closer to the highlights and shadows, and you don't lose either of them!

Before
After


You'll notice that not only has the exposure been affected, but you've had a change in color as well. If you don't like the fact that the color shifted, select the curves adjustment layer, and in the layers palette change the blending mode to Luminosity. This means it will keep color casts the same, and only change the tonal values.

Now, you may notice that the Curves tool can be broken down into channels of Red, Green, and Blue, we'll discuss that application further in Correcting Color Balance Using Curves.


Here are the other sections of this module: