Selection tools allow you to select portions of an image and to perform a variety of operations. When using Photoshop or PhotoStyler, you have a high degree of control in editing, retouching, or manipulating images. A rectangular tool allows you to select rectangular areas and a lasso tool allows you to select objects with irregular shapes. Another tool allows you to select a color from a portion of an image by clicking on it; you can clone it and replicate it elsewhere. By using these tools, you can add an aircraft formation to the image of an aircraft carrier. Then, using a blending tool, you can blend the two images smoothly. Other tools allow you to stretch or rotate images. Some programs have a magic wand tool that allows you to click inside an irregular-shaped object, and it isolates this object automatically (fig. 3-15).

FILTERS

The filter features provided in image-editing software control the image brightness and contrast as well as sharpen or soften selected portions of the image. Some programs provide a "mosaic" filter so you can convert a portion of the image into large-size pixel areas. You have probably seen this effect used for

Fiure 3-13.-Photoshop and PhotoStyler tools.

television interviews where people do not want their identity revealed.

COLOR CORRECTION

Imageediting programs also offer color correction and calibration features. These color correction features allow you to modify an image to get the best possible quality to a color printer or other output device (fig 3-16). These color corrections are accomplished by using a gamma curve.

The gamma curve represents the pixel values in the original image on the horizontal axis. The corresponding values of the displayed image are represented on the vertical axis. Separate red, green, and blue lines may be displayed so you can modify each color independently. By increasing the slope, you can raise the contrast level; this forces most of the pixels toward the light and dark ends of the spectrum. By raising or lowering the entire line, you can adjust the brightness.