Correcting Tone and Exposure - Beginning Photo Retouching and Restoration Using GIMP - page 38

Chapter 3

Correcting Tone and Exposure

In This Chapter
Common Tonal Problems •

• The Brightness-Contrast Dialog

• Tonal Corrections Using Levels

• Tonal Correction Using Curves

• Tonal Corrections Using Layer Blend Modes

Common Tonal Problems
Many old photographs have various tonal problems—low contrast, loss of detail from fading, darkening with
age, etc. Even many of the pictures you currently shoot with your digital camera could probably benefit from
tonal corrections. Sometimes, one or two adjustments are all that is needed to revive a dull photograph.
Other problems will require a greater degree of correction.
Many, if not most, of the images you work with will require some degree of tonal adjustment. Tonal
problems generally fall under one of the following descriptions:

• The image is overexposed/too bright.

• The image is underexposed/too dark.

• The image has low contrast/dull and flat.

Some images have local or mixed tonal issues. For example, an image might be properly exposed in one
area and underexposed in another.

Using the Histogram to Assess Tonality
A histogram (Figure 3-1 ) is a graphical representation of the pixel brightness values in an image, ranging
from 0 (pure black) to 255 (pure white). Factors such as image tonality and exposure determine the shape of
the histogram. Tonal correction tools such as Levels and Curves display a histogram in the window. You can
also access the histogram window by itself (Image Menu ➤ Colors ➤ Info ➤ Histogram).