Goal.

Reduce ghosting by a global contrast reduction as shown here:



Remark that the whole image is affected.

Global Deghosting in PSM.

After composing the anaglyph in StereoPhoto Maker (SPM) choose the Ghost reduced anaglyph type to open the Anaglyph Ghost dialog pop up window.

It is an implementation of the method mentioned in the introduction.
So we know what to expect.

The top half does the actual deghosting in Lab color space.
The bottom half is used to restore some of the lost contrast and brightness in RGB color space.

First we reduce the contrast ( here minus 26 ) in an attempt to make the ghosting disappear.

Most of the times it is not possible to remove it completely and also the visibility is reduced.
For these two reasons a contrast reduction almost always has to be followed by a brightness adjustment before a new attempt can be done.

A brightness of plus 30 shifts the histogram figure back to right so that the light colors are in their initial positions ( remember we want to affect dark colors only).

If the first attempt to remove the ghosting was unsuccessfull you can try again now.
If you are happy with the deghosting result you can try to restore some of the lost contrast in RGB colorspace.

With some luck some or almost all (like here, plus 26) lost contrast can be recovered.

Mostly some brightness adjustment is also required.

A brightness reduction (minus 11) is all I needed to make this anaglyph to my taste.

Restriction to remember (lets hope they evaporate soon):

• input is a stereo pair (anaglyphs not accepted yet: use IA).
  
  
• only halfcolor anaglyphs are created ( modified anaglyphs not possible yet: use IA).

Global Deghosting in IA.

Open the anaglyph in Image Analyze (IA) and click the white button to invoke the Color Mapper.

Method nr 1.

Select the Luminance color plane (= Lab) and adjust Black and White points to remove the ghosting.

If satisfied push OK.
If you want to recover some of the lost contrast and brightness push Apply instead of OK and continue with step 2 of method nr 3 .

Method nr 2.

Select the Luminance color plane (= Lab) and adjust Gamma to remove the ghosting.

If satisfied push OK.
If you want to recover some of the lost contrast and brightness push Apply instead of OK and continue with step 2 of method nr 3 .

Method nr 3 step 1.

Select the Luminance color plane (= Lab) and adjust Contrast and Brightness to remove the ghosting.

If satisfied push OK.
If you want to recover some of the lost contrast and brightness push Apply instead of OK and continue with step 2

Method nr 3 step 2.

Select the All plane (= RGB) and adjust Contrast and Brightness to restore some of the contrast and brightness.

If satisfied push OK.
.

Method nr 4.

Select the Luminance color plane (= Lab) and use the Define curve option to remove the ghosting.

If satisfied push OK.
If you want to recover some of the lost contrast and brightness push Apply instead of OK and continue with step 2 of method nr 3 .

This method is difficult to master and not suited to be repeated. Works best with only a few tones.

Summary.

If your stereo pair is not too bad, this methods will remove most of the ghosting.
Much depends on the tone dynamics: if there are only a few tones to represent dark you can expect strong contrasts while if there are many tones the contrast will be richer but not stronger.
For this reason a good digital camera or scanner makes a big difference when making anaglyphs.

Some references to convince you (if needed):

• dynamic range in scanners,
• dynamic range in digital cameras,
• the future ...now.