The N entry box controls the number of contours levels to draw.
Pressing the Draw Contours button will draw contours at the image levels currently listed in the Levels: list.
Pressing the Set Min/Max button will fill in the min and max entry boxes from the minimum and maximum values of the image.
Pressing the Make Levels will fill in the levels list with an evenly spaced list of level values from min to max excluding the min and max values themselves.
The Binning option allows the image data to be binned before the contours are computed. Contours will be computed more quickly for binned images. However, binning will cause the positions of the contours to be less accurate.
The Smooth option causes the image data to be smoothed by a Gaussian kernel with the specified sigma number of pixels before the contours are computed. This technique often is necessary to achieve good results for sparse data (e.g. event files). However, it can affect the accuracy of the contours.
The Quality radio button chooses between one of two contouring methods. The faster option selects contours with up to 4 points per pixel. The quality option selects contours with up to 8 points to pixel.