
click to enlarge
Now you need to find the shadows in your photo. Hold down the Alt key (Option key in Mac) on your keyboard, and pull the black little triangle slider on the Input level graph to the right (towards the gray slider). You will start to see the darkest area of the photo forming up. As soon as the dark area of the picture turns solid black, let go of the Alt key (Option key in Mac) on your keyboard, and release the mouse button. The changes to your photo take effect immediately.
Now hold down the Alt key (Option key in Mac) on your keyboard and pull the white little triangle slider to the left (towards the gray slider). You will start to see the lightest area of the picture forming up. Let go of Alt key (Option key in Mac) and the mouse from the slider.
Adjust the triangle sliders left-right by holding down the Alt key (Option key in Mac) until a satisfactory brightness and contrast is achieved. Click on “OK”. Go ahead and take a look at the History palette. Here you can see the photo as it was before and after the Level changes. You will see quite a difference.