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Window/Level

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Window/Level is a similar concept to "brightness and contrast".

Manually Adjusting the Window

There are a number of ways to adjust the window & level of an image:

1.Select the Window/Level Tool, and drag around on the image with the right mouse button.  Dragging up increases the "level" (or window centre), while dragging down decreases it; dragging left reduces the window width and dragging right enlarges it.  Combining both dragging motions will adjust both the window width and level simultaneously.

Dragging up moves the window of selected values to the higher end of the image's dynamic range.

Dragging left reduces the window size, selecting a smaller portion of the image's dynamic range and saturating everything outside of it.

2.Drag around on the image using the middle mouse button.  For convenience, this method is available anytime regardless of the selected tool.

Applying Presets

Some images may come with predefined windows and/or non-linear transforms (typically called "data LUTs") embedded in either the image's own headers or in an associated presentation state (such as those generated in the process of creating a key image).  There are a couple of ways to cycle through all the available presets:

1.Press the F2 key repeatedly (note the changing description in the lower left corner of the text overlay as you cycle through the available windows/LUTs).

2.Select Auto from the drop-down beside the Window/Level button.

In the case where there are multiple LUTs, both linear and data, the "Auto" algorithm cycles first through the data LUTs, then through the linear ones.

Applying User-Defined Presets

In addition to applying preset windows/LUTs included with the study, you can also define modality-specific presets that can be bound to a specific key stroke through the options dialog.  There are a couple of ways in which you can apply these custom presets:

1.Press the key to which the preset is bound, if one exists.

2.Select the desired preset from the drop-down beside the Window/Level button.

3.Select the desired preset from the context menu, under Window/Level Presets.  The previously mentioned "Auto" preset is available here as well.

Technical Notes

If you manually adjust the window/level after applying a LUT transform (or "data LUT") from the image's headers or a presentation state, you will notice that the description in the lower left changes to "Brightness/Contrast" instead of "Window/Level."  This is because the LUT transform is not necessarily linear, and cannot be thought of as window/level.  The best description is brightness and contrast values given as a percentage relative to the output of the LUT transform.
You can window/level colour images and, for consistency, the description in the lower left will still say "Window/Level."  Underneath the hood, the Vetstation performs the window/level operation on each colour channel separately.  We allow this for consistency with the operation of greyscale images because most colour ultrasound images are still predominantly greyscale.  Please be aware, however, that window/levelling a colour image actually reduces the bit-depth of the entire image, as the greyscale portion of any colour image is already 8-bit which almost any display device is fully capable of displaying.  You should therefore take care to use the tool in such a way that you are enhancing the contrast of a specific region of the image.

 

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