Adjustments analyze pixels throughout a picture and map them to different values. If you’re familiar with an adjustment or effect from another application, you’ll be comfortable with adjustment controls in QuarkXPress as well.

• If an image is too light or too dark, you can use the Levels effect to brighten highlights, compress shadows, and adjust midtones individually.
• To lighten or darken a picture, you can make precision tonal adjustments using the Curves effect. Instead of limiting adjustments to shadows, highlights, and midtones, you can adjust any point along a scale of 0% to 100% (for CMYK and grayscale) or 0 to 255 (for RGB). The precise nature of this tool requires more experience and knowledge than using the Levels effect.
• To make simple changes to the tonal range of a picture, you can use the Brightness/Contrast effect to adjust the tonality of every pixel instead of individual channels.
• Use the Color Balance effect to remove unwanted color casts or correct oversaturated or undersaturated colors. This effect changes the overall mixture of colors in a picture for generalized color correction.
• The Hue/Saturation effect is designed to adjust the overall color intensity and light in a washed-out or muted picture, but is generally used as a special effect. The picture’s current hue (color cast), saturation (intensity), and lightness (degree of white light) are expressed as zeros by default.
• To mimic an old printer’s method for correcting specific colors, you can use the Selective Color effect. This increases or decreases the amount of process color in each of the primary colors in a picture. For example, if an apple is too purple, you can take cyan out of the areas that affect red.
• For pictures intended for on-screen display (in Web layouts), you can adjust the white point using the Gamma Correction effect. Adjusting the white point controls the brightness of the picture’s display on screen. To use the Gamma Correction dialog box, adjust the midtones by entering a new value in the Gamma field or by dragging the slider. A higher value produces a darker picture, overall.

• The Desaturate effect converts a color picture to a black-and-white picture while leaving the color mode and lightness value of each pixel unchanged. For example, it assigns equal red, green, and blue values to each pixel in an RGB picture to make the picture appear grayscale.
• The Invert effect inverts the gray values of each channel in a picture. This effect is recommended for 1-bit, grayscale, and RGB pictures. Because CMYK pictures contain a black channel, this effect is not recommended for CMYK pictures. The inversion of the black channel usually results in images that are mostly black or mostly white.
• The Threshold effect converts color pictures to black and white, without using gray. Enter a value in the Threshold field or drag the slider; all pixels lighter than the threshold value are converted to white and darker pixels are converted to black.
• The Posterize effect modifies the tonal levels for each channel in a picture to produce special effects. To use the Posterize dialog box, enter a new value in the Levels field or drag the slider. For example, choosing five tonal levels in an RGB image results in 15 colors (five for each of the three primary colors).
• The Negative effect inverts the brightness and hue of CMYK pictures. Because CMYK pictures contain a black channel, this effect, rather than the Invert effect, is recommended for CMYK pictures. The inversion of the black channel usually results in images that are mostly black or mostly white. If you export the picture in another color mode (File > Save Picture), the Negative effect is not applied.