Making Color and Tonal Adjustments

Making Color and Tonal

Adjustments

Basic steps for correcting images

Photoshop and ImageReady give you a range of commands and features for adjusting the tonal quality and color balance of images. For simple image correction, use one of the quick adjustment commands. (See “Making quick overall adjustments to an image” on page 150.) For more precise and flexible adjustments, use the following color-correction workflow.

1. Calibrate your monitor.

In preparation for adjusting images, characterize and calibrate your monitor to a colordisplay standard suited to your working needs. Otherwise, the image on your monitor may look very different from the same image when printed or when viewed on another monitor. (See “Creating an ICC monitor profile” on page 117.)

2. Check the scan quality and tonal range.

Before making adjustments, look at the image’s histogram to evaluate whether the image has sufficient detail to produce high-quality output. The greater the range of values in the histogram, the greater the detail. Poor scans and photographs without much detail can be difficult if not impossible to correct. Too many color corrections can also result in a loss of pixel values and too little detail.

The histogram also displays the overall distribution of shadows, midtones, and highlights to help you determine which tonal corrections are needed. (See “Checking scan quality and tonal range (Photoshop)” on page 131.)

3. Adjust the tonal range.

Begin tonal corrections by adjusting the values of the extreme highlight and shadow pixels in the image, setting an overall tonal range that allows for the sharpest detail possible throughout the image. This process is known as setting the highlights and shadows or setting the white and black points.

Setting the highlights and shadows typically redistributes the midtone pixels appropriately. When pixel values are concentrated at either end of the tonal range, however, you may need to adjust your midtones manually. It is not usually necessary to adjust midtones in images that already have a concentrated amount of midtone detail.

There are several different ways to set an image’s tonal range:

•You can drag sliders along the histogram in the Levels dialog box. (See “Using Levels to set highlights, shadows, and midtones” on page 137.)

•(Photoshop) You can adjust the shape of the graph in the Curves dialog box. This method lets you adjust any point along a 0–255 tonal scale and provides the greatest

control over an image’s tonal quality. For more information, see “Using the Curves dialog box (Photoshop)” on page 139.

•(Photoshop) You can assign target values to the highlight and shadow pixels using either the Levels or Curves dialog box.This can be a useful method for images intended for printing on a press. For more information, see “Using target values to set highlights and shadows (Photoshop)” on page 141.

4. Adjust the color balance.

After correcting the tonal range, you can adjust the image’s color balance to remove unwanted color casts or to correct oversaturated or undersaturated colors. Examine your image with reference to the color wheel to determine which color adjustments you need to make. (See “About the color wheel” on page 146.) You can choose from the following color adjustment methods:

•(Photoshop) The Auto Color command automatically corrects the color balance in an image. For more information, see “Using the Auto Color command (Photoshop)” on page 151.

•(Photoshop) The Color Balance command changes the overall mixture of colors in an image. For more information, see “Using the Color Balance command (Photoshop)” on page 146.

•The Hue/Saturation command adjusts the hue, saturation, and lightness values of the entire image or of individual color components. (See “Using the Hue/Saturation command” on page 147.)

•(Photoshop) The Replace Color command replaces specified colors in an image with new color values. See “Using the Replace Color command (Photoshop)” on page 149.

•(Photoshop) The Selective Color command is a high-end color-correction method that adjusts the amount of process colors in individual color components. For more information, see “Using the Selective Color command (Photoshop)” on page 149.

•The Levels dialog box lets you adjust color balance by setting the pixel distribution for individual color channels. In Photoshop, you can also use the Curves dialog box to make these adjustments. For more information, see “Using Levels to adjust color (Photoshop)” on page 139 and “Using the Curves dialog box (Photoshop)” on page 139.

•(Photoshop) The technique of blending colors from different channels can also produce color adjustments. For more information, see “Mixing color channels (Photoshop)” on page 271.

(Photoshop) To best preserve the original detail in your image as you make color adjustments, convert the image to 16 bits per channel. (See “Converting between bit

depths” on page 93.) When you finish making color adjustments, convert it back to an 8-bit-per-channel image.

5. Make other special color adjustments.

Once you have corrected the overall color balance of your image, you can make optional adjustments to enhance colors or produce special effects. (See “Applying special color effects to images” on page 152.)