The Level tool provides features similar to the Histogram tool but can
also change the intensity range of the active layer or selection in every
channel. This tool is used to make an image lighter or darker, to change
contrast or to correct a predominant color cast.
5.6.1. Activating the Tool
You can get to this tools in several ways:
In the image menu through
→ → .
In the image menu through
By clicking on the tool icon
in the toolbox if this tool has been installed there. For this, go
to Tools Dialog.
Figure 13.140. Level tool options
You can save the color settings of your image by clicking the
button opens a menu:
Figure 13.141. Preset Menu
which lets you Import Settings from File or
Export Settings to File,
and gives you access to the Manage Save Settings dialog:
Figure 13.142. Manage saved Settings Dialog
You can select the specific channel which will be modified by the
Value makes changes to the value of
all RGB channels in the image: the image becomes darker or
Red, Green and
Blue work on a particular color
channel: the image gets more or less color. Remember that
adding or removing a color result in removing or adding
the complementary color
Alpha works on semi-transparent layers
or selections: here, dark means more transparency, and
white is fully opaque. Your image must have an Alpha
Channel, otherwise this option is disabled.
Initialize channel cancels changes to
the selected channel.
The main area is a graphic representation of the active layer or
selection dark (Shadows), mid and light (Highlight)tones content
(the Histogram). They are on abscissa from level 0 (black) to
level 255 (white). Pixel number for a level is
on ordinate axis. The curve surface represents all the pixels of
the image for the selected channel. A well balanced image is an
image with levels (tones) distributed all over the whole range.
An image with a blue predominant color, for example, will produce
a histogram shifted to the left in Green and Red channels,
signified by green and red lacking on highlights.
Level ranges can be modified in three ways:
Three triangles as sliders: one black for dark tones
(Shadows), one grey for midtones (Gamma), one white for light
The black slider determines the black point
: all pixels with this value or less
will be black (no color with a color channel selected /
transparent with the Alpha channel selected).
The white slider determines the white point
: all pixels with this value or
higher, will be white (fully colored with a color channel
selected / fully opaque with the Alpha channel selected).
The gray slider determines the mid point.
Going to the left, to the black, makes the image lighter
(more colored / more opaque) . Going to the right, to the
white, makes the image darker (less colored / more
Two eye-droppers: when you click them, the mouse pointer
becomes an eye-dropper. Then clicking on the image determines
the black or the white point according to the chosen
eye-dropper. Use the left, dark one to determine the
black-point; use the right, white one to determine the white
Three numeric text boxes to enter values directly.
Input Levels are used to lighten highlights (bright tones),
darken shadows (dark tones), change the balance of bright and
dark tones. Move sliders to the left to increase lightness
(increase the chosen color / increase opacity). Move the sliders
to the right to lessen lightness (lessen the chosen color /
Examples for Input Levels
The original image is a gray-scaled image with three stripes:
Shadows (64), Mid Tones (127), Highlights (192). The histogram
shows three peaks, one for each of the three tones.
The Value channel is selected. The black slider (Shadows) has
been moved up to the Shadows peak. The 64 value became 0 and
the Shadows stripe became black (0). The Gamma (mid tones)
slider is automatically moved to the middle of the tone range.
Mid tones are made darker to 84 and Highlights to 171.
The white slider (highlights) has been moved up to the
highlight peak. The 192 value became 255 and the highlight
stripe became white. The Gamma (mid tones) slider is
automatically moved to the middle of the tone range. Mid tones
are made lighter to 169 and Shadows to 84.
Output levels allows manual selection of a constrained output
level range. There are also numeric text boxes with arrow-heads
located here that can be used to interactively change the Output
Output levels force the tone range to fit the new limits you have
Working with Value: values are compressed and look more
alike; so contrast is reduced. Shadows are made lighter:
new details can show up but contrast is less; a compromise
is necessary. Highlights are made darker.
Working with Color channels: if you the use the green
channel for example and set the output levels between 100
and 140, all pixels with some green, even a low value, will
have their green channel value shifted between 100 and 140.
Working with Alpha channel: all Alpha values will be
shifted to the range you have set.
Example for Output Levels
The original image is a RGB gradient from black (0;0;0) to
white (255;255;255). Output Levels has no histogram; here, we
→ → .
Value channel selected. The black slider has been moved to 63
and the white slider to 189. The Histogram shows the
compression of pixels. No pixel is less than 63, and no pixel
is more than 189. In the image, Shadows are lighter and
Highlights are darker: contrast is reduced.
Open: This button allows you to
select a file holding level settings.
Save: Allows you to save any levels
you have set to a file that can be loaded later.
Auto: Performs an automatic setting
of the levels.
Three eyedroppers: These three buttons
respectively represent a white, a gray and a black eye-dropper.
When you click one of these buttons, the mouse pointer takes the
form of the eye-dropper it represents. Then, when clicking the
image, the clicked pixel determines the white point
, the black point or the
mid point according to the eye-dropper you
chose. Works on all channels, even if a particular channel is
Figure 13.143. Example for Levels eye-droppers
Edit these settings as Curves
To make your work easier, this button lets you turn to the
Curves tool with the same
The Preview button makes all changes to the levels dynamically so
that the new level settings can be viewed straight away.
5.6.3. Tool Options dialog
Figure 13.144. “Levels” tool options
Although this tool is not present in Tool box, nevertheless it has a
Tool Option Dialog under the Toolbox. These options are described here:
These two options have the same action as the logarithmic and
Linear buttons in the Levels dialog.
This slider sets the “radius” of the color-picking
area. This area appears as a more or less enlarged square when
you maintain the click on a pixel.
Figure 13.145. A very under-exposed image
Figure 13.146. Setting the white point
Figure 13.147. Setting the balance between Shadows and Highlights