Colour matching is not available during Image To User Coordinates tie down as there is no georeferenced image database to which to radiometrically correct. Likewise, colour matching is not useful during Image To Vector tie down if there is no georeferenced imagery to which to correct. Colour matching is also inappropriate if working with pseudo-coloured images, shown as the mode option menu on the image windows being set to ``PCT''.
The colour matching LUT is computed by calculating an LUT that will match, as closely as possible, the histograms over the sample areas of imagery. The sample area is shown as a red box on each of the overview windows, and it defaults to the whole database. This area can be reselected by dragging out a box with the left mouse button in either or both overview windows.
The colour matching LUT is not actually computed until the ``Match'' button at the bottom of the panel is selected. At this point, a new LUT is computed based on the current sampling windows. The new LUT is applied to the uncorrected imagery and updated in the ``Colour Matching LUTs'' area of the panel.
The panel also contains a ``Background'' value editable field, to set a grey level value that should be excluded from the histogram which is used to compute the colour matching LUTs. Note that 0 and 255 values are already excluded from the histogram.
The ``File'' pulldown of the ``Colour Matching'' panel contains options to load and save the colour matching LUTs. These options may be used to import radiometric matching LUTs developed in EASI/PACE or possibly other software.
See Also: Theory of Mosaicking