Contents - Index - Previous - Next

Chromatic Correction

Operation is similar to that of manual radial correction on all colours at once as described under Manual Correction.

Click on the Chromatic button to permit you to correct chromatic aberration manually. 

The three constants which control distortion correction are modified by  a set of track bars which permit you to change the values positively or negatively around zero by a small amount. You can change each colour component separately. An additional track bar controls 
marked "d" enables changing all of the a, b and c constants for each of red, green or blue colours simultaneously. It is strongly recommended to change the value of the "d" trackbars for each color before attempting to use the a, b or c trackbars.

Hold down the left mouse button and a small frame appears. 

Move this to an area where you can see chromatic aberration along the vertical or horizontal sides of a high contrast feature in the image in Profile mode.During this operation, zooming with the left mouse button is disabled. Release the mouse. The area will be enlarged to fill the whole window. You can return to the full-view image with a right mouse click, and this will reset all visible parameters to the initial values visible when the Chromatic button was clicked.

Examine the colour of the chromatic fringe around the feature, and start by dragging the d button of one of the colour choices in red, green and blue. Watch the feature and if the fringe is reduced, continue dragging until it is minimised. Then, go to the next colour and repeat until all colour fringing has been eliminated. With great care, you may also modifiy the values for a, b, or c for local special correction, but this is normally not recommended.

When you have reached a satisfactory solution, you should save the correction profile to a file whose name describes its function.


Bilinear interpolation is always used when applying the chromatic correction to the whole image regardless of the setting of the interpolation check box, but nearest neighbour interpolation with possible slight jaggedness is always used on the magnified window image for speed of reaction when dragging a slider. If you have a slow machine which does not respond quickly to the drag operation, use the left and right arrow keys on the numeric keypad after clicking once on the slider of interest. This gives single step operation and finer control.