# Reference Points

The Reference Points tab provides a table control that lets you view and set the exact value of all reference points.

To add or delete a reference point, use the two buttons at the top of the table. To modify a reference point, click on the value to modify and enter the new value.

Note: The Relative input and output values allow you to specify the reference points as a fraction of the range of pixel values in the image (input and output). If the input or output image type changes, the absolute (pixel value) values are adjusted automatically to conform to the relative values that you supply.
Note: The control enforces the requirement that the mapping function be monotonically increasing (each successive reference point must have an X-value greater than or equal to the preceding point).

Parameter | Description
--- | ---
Relative Input | Specifes the input value for a reference point as the fraction (0.0 through 1.0) of the range of pixel values supported by the input image type.
Relative Output | Specifes the output value for a reference point as the fraction (0.0 through 1.0) of the range of pixel values supported by the output image type.
Absolute Input | Specifes the input value for a reference point as a pixel value.
Absolute Output | Specifes the output value for a reference point as a pixel value.