Window Leveling
Window leveling offers the opportunity of changing density relationships — brightness and contrast — within images to obtain the most useful information. Window leveling in Dragonfly behaves in a manner closest to medical imaging by interactively adjusting the window (contrast), which is the range of minimum and maximum values, and the level (brightness), which is the position of the selected range in the intensity space. Additional controls let you adjust the gamma, which determines how tones are displayed by defining the relationship between input values and the resulting image luminance.
The Window Leveling panel, shown below, offers precise control for selecting the threshold values and window position, as well as the applied gamma correction.
Window Leveling panel
You should also note that window leveling is applied simultaneously to all 2D views of the selected dataset in the current scene and can be adjusted separately for the 3D view.
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Icon |
Description |
|---|---|---|
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Histogram |
- - |
The histogram at the top of the panel shows how values are distributed within a dataset. The darkest parts of the image will appear on the left side of the graph, the mid-tones will appear in the middle, and the brightest parts (highlights) on the right side. If required, you can select the Log Y option to plot the Y-axis in log scale. |
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Threshold values |
- - |
The two numbers under the histogram are the minimum and maximum threshold values. These two values define the display range, or window. |
| Window Level |
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Lets you adjust window leveling of the selected dataset. |
| Area |
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Allows you to apply leveling computed within a selected area on a 2D image to the whole image in the 2D views of the selected scene. |
| Reset |
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Resets the original window leveling values. |
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Local gamma |
- - |
The gamma curve, which is shown on the Window Leveling histogram, determines how tones are displayed in a view by defining the relationship between input values and the resulting image luminance.
As shown in the following illustration, adjusting gamma will affect the perceived brightness of an image by making dark regions lighter. You should note that the local gamma typically rises from 1.0 to about 2.0.
You should also note that while gamma affects the brightness of a display, it is not identical to brightness. This is because gamma adjustments are not linear, like brightness levels are. Instead, the gamma setting applies a function to the input levels to produce the final output level. This means that the extreme dark and light points are not as affected as the mid-tones, which are enhanced more because of the non-linear function. Gamma can be adjusted for each view in a scene with the slider or by changing the current value.
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Adjusting Window Leveling
You can adjust window leveling with the interactive Window Level text annotations, the Window Level tool, or in the Window Leveling panel.
How to Adjust Window Leveling
- Select the required image data in the Data Properties and Settings panel.
- Do the following to adjust window leveling with the interactive text annotation:
- Drag the annotation left and right to change the threshold values (window width value).
- Drag the annotation up and down to change the center value.
- Do the following to adjust window leveling with the Window Level tool:
- Click the Window Level
button on the Window Leveling panel.
Click inside the required view and then drag up or down to change the window center value; drag left or right to change the window width value.
- Open the Window Leveling panel and then make your adjustments as follows:
Drag the Range sliders to change the threshold values. Drag the area between the sliders to change the window center value.
You can also enter threshold values in the Edit boxes below the histogram.
- Click the Window Level
- Do the following to adjust window leveling in the Window Leveling panel:
- Open the Window Leveling panel.
- Drag the left or right side of the window superimposed on the histogram to change the threshold values.
- Enter threshold values in the Min and Max edit boxes below the histogram.
- Drag the window to change the center value.
- Adjust the gamma with the slider or by changing the current value.
- Do the following to apply leveling computed automatically within a selected area on a 2D image:
- Click the Area
button in the Window Leveling panel. - Click and drag to define a rectangular area on a 2D image of the selected dataset.
- Release the mouse button to apply the leveling values computed for the selected area.
- De-select the Area button.
- Click the Area
- Click the Reset
button to reset leveling to the original values, if required.
Configured Actions for Window Leveling
A number of configured actions and keyboard shortcuts are available for window leveling. The default settings for these actions are listed in the following table.
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Action* |
Key |
Mouse |
|---|---|---|
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Adjust window leveling in Window Leveling mode |
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Left mouse |
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Adjust window leveling in Window Leveling Infinite mode |
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Left mouse |
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Define an area to compute window leveling |
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Left mouse |
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Adjust leveling in any mode |
Left Ctrl |
Right mouse |
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Switch to Window Leveling Area mode |
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Switch to Window Leveling mode |
Space Bar |
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Define an area to compute window leveling from any mode |
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Adjust window leveling gamma in any mode |
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