This chapter described many ways you can lighten, darken, and change the contrast in images. Following are key concepts:
You can lighten images with Curves, Levels, the Clone tool with Screen blending mode, the Dodge tool, and with the Screen blending mode used on layers. You can darken images with Curves, Levels, the Clone tool with Multiply blending mode, the Burn tool, and with the Multiply blending mode used on layers.
Generally, increasing contrast means making lighter areas lighter and darker areas darker. An image with more contrast usually seems to have more detail and pop off the page. You can increase contrast by steepening part of a Curve, dragging the Input Levels sliders inward, using the Dodge and Burn tools, and using the Soft Light blending mode.
Decreasing contrast in an image usually makes it appear to have less detail and appear more subtle. You can decrease contrast by making part of a Curve less steep, dragging the Output Levels sliders inward, and lowering the opacity of various kinds of layers.