Edit
an Image Using Levels
Easy PhotoShop Tutorials
Here's your LEVELS screen,
that is going to pop up when you click Image >> Adjustments >>
Levels
You can also use Ctrl and L on your keyboard for a
shortcut.
What you will see is a bar graph of the colors in your picture.
You can move the arrows with your mouse to lighten or darken your photo, but we're not going to do that. We're going to click the button to the far right with the eyedropper on it.
Your mouse arrow then turns into an eyedropper, and what we want to do, is click the eyedropper on the part of your photo that is suppose to be white. Continue the tutorial on How to Use Photoshop Levels