Controls on the the Color Adjustments
(Whole Image) window allow you to manipulate the brightness, contrast,
and gamma
of an image, as well as its hue, saturation, and lightness. To access
this window, select Color/Adjust from the
image menu.
The controls consist of a list of possible adjustments at the top, three scrollbars below, and a Preview box that, when checked, allows you to see the effect of each adjustment as you make it. When you select an adjustment on the list, the scrollbars reconfigure to reflect the choice, and are relabeled accordingly.
Note 1: The standard "color model" on a computer is called RGB, for Red-Green-Blue. This is because each color in an image is represented with 3 numbers, one for the intensity of each of these "component" colors. Black is 0-0-0, white is 255-255-255, and all others lie somewhere in between. Adjusting the color is equivalent to fiddling with these values.
Note 2: As with all Easel edits, none of these adjustments actually change the image. Instead, they are instructions used to display/print the image, and as such, they can be instantly reversed. See How Easel Works for more info, and don't be afraid to experiment.
Note 3: These adjustments affect all colors in an image the same way. If you want to manipulate different parts of the image differently (e.g. make the shadows darker but leave the highlights untouched) see Adjusting Color by Zone.
When Adjust for All Colors is selected, the three scrollbars are labeled Brightness, Contrast, and Gamma, with the midpoint of each the neutral position. Slide the "thumb" to the right to increase the value, to the left to decrease it. When these scrollbars are moved, the value is changed for each of the "components" so that the ratio between the R-G-B numbers remains constant.
Although it of course depends on the image, I've found
that the most generally useful adjustments are increasing the brightness
10-20% or so, and the contrast 20-40%.
When you select any of the Adjust.. by Color settings, the scrollbars are relabelled to correspond to the color components: Red, Green, and Blue. This allows you to adjust them separately. To be honest, I've never found this particularly useful, but pretty much all image editors include it, so I figured what the heck.
Without getting into detail, Hue-Saturation-Lightness is another 3 component color model, and when you select it, the three scrollbars control hue, saturation, and lightness, respectively. Small tweaks in saturation can enhance the richness of colors in an image, making a blue sky really blue for example. Larger changes make for some weird effects, as do changes in hue. The lightness slider can sometimes do a better job than brightness at lightening up an image. Don't be afraid to experiment, as any changes can be effortlessly undone.