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#### Understanding Look-Up Tables and Window/Level values

Adjusting the image contrast and brightness enables you to review a particular pathology. You can also adjust the contrast and brightness of US images, to compensate for poor gain settings when the images were captured.

The image contrast and brightness are determined by the following factors:

| • | The Look-Up Table (LUT) function, which is used to display the image on the window

| • | The Window/Level values of the image

You can specify the extent to which Window/Level values and LUT function are applied. See Specifying the Window/Level scope.

How Look-Up Tables are used

An image is composed of a large number of pixels, each corresponding to a point in the image. When displaying images on the screen, the Disc Advanced Viewer uses a Look-Up Table (LUT) function to map the image pixel values to the display values. For grayscale images, the display value is the relative brightness. As a result, the pixels are displayed on the screen with different brightness and contrast.

You can adjust the image contrast and brightness by applying different LUTs. See Selecting a LUT function to apply.

Note: The pixel values for CT and CR/DR/DX images are converted to pixel intensity values. See Understanding the intensity unit.

Understanding Window/Level

Window and Level are image processing parameters that define how captured image intensities are displayed on the screen.

The display values of displayed images lie in a particular range. This range determines the brightness of the pixels:

| • | All pixels with a value below this range are black

| • | All those with a value above this range are white

| • | All pixels within this smaller range are shades of grey

The range of 0-255 is the range within which the human eyes can detect noticeable luminance changes. A smaller range can be used to display certain features in an image more clearly. For example, if this “sub” range was from 100 to 150, then all pixels with values less than 100 would appear black, while all those with values greater than 150 would appear white. Pixels between 100 and 150 would appear grey.

Window and Level relate directly to this “sub” range of pixel values:

| • | Window is the total width of the sub-range (50 in the above example). Window controls the contrast of an image.

| • | Level is the average (middle) value of the sub-range (125 in the above example). Level controls the brightness of an image.

You can adjust the image contrast and brightness, by adjusting the Window/Level. See Adjusting the Window/Level values.

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