Correcting Tone and Exposure - Beginning Photo Retouching and Restoration Using GIMP - page 42

Figure 3-5. Most of the data is spread throughout the histogram
Tonal problems could be due to improper lighting or exposure settings, or in the case of old
photographs, chemical changes in the print itself over time. Old photographs will often have mixed tonal
issues, such as uneven fading, which can make correction more complex and challenging.
Using the Color Picker Tool to Track Tonality
As mentioned in the Introduction, software to calibrate your monitor can be very helpful to display an image
as accurately as possible. However, it's a good idea to take measurements for an accurate readout of what
pixel values you are seeing. What you see on your monitor may differ some from reality.
The Color Picker tool is used to sample areas to determine color values and tonal values. In the
grayscale image in Figure 3-6 , several areas have been sampled to determine the gray value (percentages)
in various areas. A grayscale image (as displayed on a monitor) is made up of equal amounts of red, green,
and blue light (you'll learn more about color models in Chapter 4). Using the eyedropper to sample pixels
will display the brightness value from 0 to 255, and also the RGB values. You can sample a single pixel, or an
average of a radius of pixels you set the parameters for.