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.
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!
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:
- Main Exposure Page - Discusses basic exposure issues in digital images, including histograms.
Using Levels to Correct Exposure - Covers the power of levels as an adjustment layer to correct underexposed and slightly over exposed images. This is my favorite method.
- Using Contrast/Brightness to Fix Exposure Corrections - Having used one of the above methods to correct exposure, the image may become flat and without contrast. This will fix it!
- Using Curves to Add Contrast - A better, more controlled approach to adding contrast. It "pinches" shadows and highlights rather than clipping off information.
- Dodging and Burning - There are many known ways to do this in photoshop, including using the tool of the same name. However, we won't discuss that tool, we'll be using a more powerful method that involves layers. This allows it to be turned up or down and on or off!