Photo Editing Guide Part 3 - The Enhance Options
Brightness Levels Histogram
A Brightness Levels Histogram is basically a plot of the brightness levels of all the pixels in the image, from the darkest on the left to the
lightest on the right. The more pixels that are a given brightness, the higher the chart value. It’s a great way to see the distribution of bright-
ness levels of your picture, at a glance, and to see the effect of these controls on the brightness distribution.
As you adjust any of the brightness controls, the histogram changes, showing you the original levels (the darker red area in the above case)
and then overlaid this a lighter semi-transparent adjusted levels (the lighter pink in the above example). So this means as you adjust the
controls you get instant feedback of how your brightness levels distribution is affected.
In the following examples, each photo is shown with the results of the enhance operation, and under each is the histogram of the brightness
levels with an explanation. Of course, you do not need to use or even see the Brightness Levels Dialog (described below on the last page of
this tutorial) and the histogram - you can just adjust the controls until the picture looks right to your eyes. But it’s educational to understand
and see a visual graph of the changes.
The brightness control adjusts the overall brightness of the image, but unlike the brightness control in most photo editors that brighten all
values equally, this puts greater emphasis on the darker shades in your picture.
The green line represents how the brightness levels are adjusted. In the initial image (left example) there is no adjustment - it’s a straight line.
In the center image where the brightness value is increased you can see that the left end (darker shades) are lifted, but the brighter shades
(right end of the line) are hardly changed - the line is very close to the original. In the case of the darker right-hand image, the green line
curves downwards indicating that all the shades have been made darker.
Increased contrast means making the lighter shades lighter and the darker shades darker. Reduced contrast is the opposite. At extreme low
contrast, almost all the image is mid-tone gray.