To create an image from a FITS Bin Table, the user needs to specify a binning factor, binning buffer size, and the binning function.
The Binning (or Block) Factor is defined as the following: A value greater or equal to zero. This value indicates the number of pixel values that will fall into a particular bin.
The Bin Buffer Size is overall size of the image generated. This has no relation to min and max values of the columns used to create the image.
The Bin Function is defined as the following: Average - all pixel values that fall into one pixel bin are averaged. Sum - all pixel values that fall into one pixel bin are summed.
Bin to Fit Frame will calculate a bin block factor as a power of 2 that will allow the entire data space to be displayed in the current frame.
By default, DS9 will bin about the center of the image. To determine the center of the image, DS9 will look for the following keywords in order:TDMIN/TDMAX
If no valid keywords are found, DS9 will define the center as the middle of the possible data space based on the coordinate data type.