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### Selecting a LUT function to apply

When displaying images on the screen, the Disc Advanced Viewer uses a Look-Up Table (LUT) function to map image pixel values to display values.

Note: Changing the LUT function does not affect the Window/Level values.

Types of LUT functions

The following table describes the four LUT functions that you can apply.

LUT function | Meaning
Linear | Image pixel values are mapped to their corresponding display values in a linear fashion.
Gamma | A non-linear LUT function. See Optimizing image presentation with non-linear LUT functions.
H&D | A non-linear LUT function. See Optimizing image presentation with non-linear LUT functions.
Sigmoid | A non-linear LUT function. See Optimizing image presentation with non-linear LUT functions.
External | Image pixel values are mapped to their display values using a Value of Interest (VOI) LUT provided by the image device. The External LUT function is stored in the DICOM header. A VOI LUT is associated with a particular view of the image and is used to outline certain properties of the image. Typically, it is used to enhance the contrast of a specific tissue type on the image. For example, for a CT image, the VOI LUT can specify a range of Hounsfield Units (HU) for bone density, so that only image values for bone tissues are displayed. Note: You can apply the External LUT only if a Source Window/Level is selected, and it is an external LUT. In addition, the External LUT is applied to the selected images only. For details on Source Window/Level, see Source Window/Level.

Steps for this task

To select a LUT function:

| 1. | Click the image to which you want to apply the LUT function.

| 2. | Click the W/L icon on the main toolbar.

The Window/Level panel is displayed.

For other ways to display the Window/Level panel, see step 1 of Specifying the Window/Level scope.

| 3. | Click the Type box, and then select the LUT function you want to apply. For details on LUT functions, see Types of LUT functions.

Two outcomes are possible:

| • | If the External LUT function is selected, it is applied to the selected images.

| • | If another LUT function is selected, it is applied within the Window/Level scope of your choice. You can also select another scope. See Specifying the Window/Level scope.

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