Documentation

Levels

The Levels adjustment can be used to alter the color range (or "exposure") of an image, including gamma adjustments, on a channel-by-channel basis. Most adjustments performed using levels consist of changing a pictures input and output white point, black point, and grey point. The white point of an image is the brightest color that appears in the image, while the black point is the darkest color that will appear in an image. The grey point represents the average color of the entire image. Each of these color points of an image may be adjusted using Levels.

Levels

Original Image

Interface

As you can see in the dialog above, the Levels adjustment is split in half, the left side represents Input (your original image) and the right side represents output (your image after levels adjustment). On the left side there are two color swatches, each with a numeric representation. These indicate the input white and black points. These colors may be adjusted using the numeric inputs, the slider, or by double-clicking on the color swatches.

The white point on this side is the color that should be adjusted to become the white point selected on the right side. When the adjustment is performed, colors in the image as bright or brighter than this color will adjust to be equal to the output white point (in the above screenshot, the output white point has been left at its default value, white). The same process occurs for the grey and black points.

In the dialog above, the output grey point has been adjusted to be slightly brighter (shown by the brown swatch). While this does not affect the whites and blacks of the image, it causes the overall color of the image to be brightened.

Example

Lighter Curves

The original image


Lighter Curves

The output grey point of the Levels is adjusted to brighten the image


Lighter Apple

The resulting image

With Level's default settings, the output histogram will be equal to the input histogram. Every adjustment that is performed on the image will cause the output histogram to be updated to represent the changes that will result in the output image. Causing the output histogram to be spread thinner results in an image with higher contrast. Compressing the histogram to a single peak, on the other hand, will result in an image with very low contrast. The histogram for the image above has been stretched very thin, as evident from the high contrast.

Up to this point, all adjustments have been performed on a all channels, red, green and blue. By using the R, G, B checkboxes (pictured below), individual channels may be adjusted separately (as well as two at a time).

Example

Lighter Curves

The original image


Lighter Curves

The gamma has been adjusted for the green and blue channels at the same time, causing the level of cyan in the image to drop overall, which accentuates the red of the image


Lighter Apple

The resulting image