Levels

To refine your image to have full contrast and to adjust the image brightness, use the Levels Adjustment tool. It's the best tool for defining black and white points, making the overall image lighter or darker, and doing color correction. To access the Levels dialog, select Layer>New Adjustment Layer>Levels.

As illustrated, the Levels dialog contains a Histogram with slider controls. You'll learn more about the use of the sliders with individual-channel Histograms, color, and eyedroppers in the Advanced Options chapter. For now we'll only address the operational function of:

■ The Black-point slider.

■ The Midpoint slider.

■ The White-point slider.

The black-point slider can be moved to set which pixels set to pure black. All the pixels represented in the Histogram directly above the black-point slider (and those to its left) will be changed to pure black, and all the other pixels in the image will be shifted darker towards the black point making the image darker.

The white-point slider similarly sets the pure-white pixels and makes the image brighter.

Adjusting both the black and white-point sliders stretched the image towards both the black and white ends, resulting in an increase in image contrast.

■Options for auto color

Eyedroppers

Black-point Midtone White-point

■Options for auto color

Eyedroppers

Black-point Midtone White-point

These pixels are These pixels are made pure black shifted darker

The midpoint slider sets the middle-gray pixels. At the same time, it sets all the pixels to the left darker then middle gray and those to the right brighter than middle gray. This may seem counter intuitive since you slide the midpoint slider towards the white slider to make the image darker, but the image preview displays the change to the image as you adjust it.

Pixels darker than middle gray

Pixels lighter than middle gray

Pixels darker than middle gray

Pixels lighter than middle gray

The preview checkbox is key to all the dialogs in Photoshop. Turn it

0 Preview on to see the effect of the current dialog in the image window, and off to see the image before this effect. (Windows toggles this action via alt +P.)

This is great for checking out subtle changes to your image before you save them.

The levels dialog is commonly used with two basic adjustment types: setting black and white points, and changing image brightness.

The Black and White point adjustment is very simple: merely drag the Black and White-point sliders in far enough so the images has some black pixels and some white pixels. This is often the single best adjustment you can make to an image since it ensures good overall contrast.

The Brightness adjustment is similarly very simple: merely drag the midpoint slider to the left or right to alter overall image brightness.

One of the advantages of Levels adjustment is it allows changes to the brightness of midpoint pixels without major changes to shadow (black) or highlight (white) pixels. This is why you should use the Levels dialog to adjust brightness and notthe Brightness/Contrast dialog.

0 0

Post a comment