Operation Manual

Understanding How to Read Histograms
The histogram is a graph that displays relative brightness in an image, from pure black
to pure white. The area under the graph represents all the pixels in the image. From left
to right, the histogram describes the range of dark pixels (shadows), gray pixels (midtones),
and bright pixels (highlights) in the image. The shape of the histogram graph depends
on the tonality of the scene and the exposure.
Pixels increase
Shadows HighlightsMidtones
Brightness increases
A histogram can also be used as a tool to evaluate whether or not there is enough shadow,
midtone, and highlight information in the image. Aperture provides three histograms in
the Adjustments inspector and the Adjustments pane of the Inspector HUD. The histogram
above the adjustment controls indicates the current state of the image. The Levels
histogram included with the Levels adjustment controls provides a way to adjust the
brightness values in the image in relation to the displayed histogram. You use the Levels
controls to adjust the shadow, dark quarter-tone, midtone, light quarter-tone, and highlight
values independently of each other without affecting the other areas of the image. The
Curves histogram included with the Curves adjustment controls provides a way to adjust
the tonal values in the image in relation to the displayed histogram. You use the Curves
controls to adjust the full range of tonal values independently of each other without
affecting the other areas of the image.
For more information about performing Levels adjustment, see Working with the Levels
Controls. For more information about performing Curves adjustment, see Working with
the Curves Controls.
469Chapter 16 An Overview of Image Adjustments