TerraPhoto User Guide

Derive image corrections

Derive image corrections command derives a brightness distribution correction for images. The correction removes systematic effects from raw images caused by sun hot spots. The effect can occur in airborne images where the sun is brightening up a part of each raw image depending on the flight line direction. It shows up, for example, in the final orthophoto mosaic as a striped pattern in small-scale displays.

Before the software is able to derive correct brightness corrections depending on the flight line direction, the raw images must be assigned to groups. The groups are created based on the sun direction. See Assign groups command for detailed information about raw image groups.

Additionally, color points must be available. The brightness distribution correction is actually a grid of correction values derived from color point values. The systematic brightness distribution correction is stored as percentage values for each image in the image list file. The color points are modified and recomputed as well.

To derive image corrections:

1. Select Derive image corrections command from the Tool pulldown menu.

This opens the Derive image corrections dialog:

2. Select settings and click OK.

This starts the derivation of the correction values. Afterwards, the color points are recomputed. A processing window shows the steps that are performed.

When the process has finished, an information dialog is show.

3. Save the color points using Save or Save As commands from the File pulldown menu in order to save the recomputed color points into a file.

4. Save the image list using Save list or Save list As commands in order to save the image list into a file including the systematic brightness correction values.