It is composed of several areas. There is a section for controlling which histograms are shown in the drawing area, as well as how the histogram is computed. The main editing area contains a large graphical representation of the LUT for interactive editing with the mouse. To the right of the main editing area is a another LUT graph showing a backup LUT copy. Below this is an area for applying a mathematical function to the LUT. Finally, there are textfields that can be used to enter LUT values directly. The panel features a button at the bottom of the panel which will apply the lookup table to the image plane, changing the image data permanently.
There are two histograms of interest: the original image data histogram, with no LUT applied, and the new histogram, with the LUT applied. Using the ``Showing'' option menu, it is possible to choose which of these histograms is drawn in the main editing area. This option does not apply to the LUT Editing panel with the ``postage stamp'' LUTs.
Using the ``Compute From'' option menu, the user may select a mask from under which to compute the raw or (pre-LUT) histogram. Possible selections include ``All Data'' for a histogram of the entire image plane, ``Viewed Data'' for a histogram of the area currently showing in the main image window, or a specific graphic plane for a histogram of the imagery underneath that graphic plane. The histograms shown in the LUT graphs are intended as an aid in setting function end points, and visualizing data distribution.
The black line represents the values in the lookup table, with the left side of the graph representing an input value of 0, and the right side of the graph an input value of 255. The height of the white line above the bottom of the graph corresponds to the output value. At the bottom the output value is 0, while at the top the output value is 255.
The first is to click and drag the left mouse button in the graph area to trace out a section of the LUT. When the left button is released the modified LUT will be applied to the imagery in the main image window. This technique is called direct tracing. While the mouse is moved through the graph, the current position of the cursor is shown in the title bar for the lookup table.
The second method, piecewise interpolation, is performed by pressing the middle button at one point, and dragging out a straight line to a second point.
The third technique allows the user to drag the entire LUT to the left or the right. This is done by pressing the right mouse button in the graph area, and dragging the whole graph left or right before releasing the mouse button. This can also be accomplished in single step increments using the ``left arrow'' and ``right arrow'' buttons while the editing area has input focus.
On motif systems, the drawing area can usually be given input focus by clicking the mouse in it. Alternately, the tab key can be used to traverse the tab groups until the drawing area is selected. Unfortunately, the drawing area will not be highlighted in any special way when it is selected so the user may have to experiment with the arrow keys until it is clear that the drawing area has input focus.
Currently there is no provision for moving the whole LUT up or down.
The markers along the left side of the graph determine the minimum and maximum output grey level values, while the markers along the bottom of the graph determine the range of input data values within which the function is applied. The markers can be moved by clicking on them and dragging them. The values can also be entered directly with textfields.
If the function name ends with ``w/Tail'', this means for regions outside of the minimum and maximum grey level values (i.e. horizontal markers), the tails will be set to the end point values. If the function names ends with ``Piece'', this means that only the LUT values between the minimum and maximum grey level values will be affected. All other parts of the LUT will remain unchanged.