Posterization occurs when you take a picture and try to
stretch the existing colours to fill a wider colour space.
This stretching occurs when you increase the Brightness or
Contrast of a frame to make it match it's neighbours more closely.
You could try smoothing the offending frame with a Lowpass filter but then you
would loose some sharpness. The best solution is to take the
original photographs with accurate exposure settings, i.e. to take maximum
advantage of the available colour range.
The green background in this small fragment of the Columbine
Stack should not have the 'colour steps' in it. In this case the
steps arize because the background looks different between frames.
There are two solutions offered by CombineZ5. First the steps can be
smoothed out by using 'Interpolated Output' on the Stack menu. This
avoids abrupt changes from one Frame to the next by mixing the colours from the
two frames together when the Depthmap values lies between them.
As you can see there is a definite improvement.
The second aproach is to make the colour and brightness of the
Frames involved similar, to do this use the 'Local' version of 'Balance Colour
and Brightness' whis on the Stack menu.
Of the two methods this is the more satisfactory, combining them both gives even
better results. A drawback of this function is that it can take a
long time to execute.
Another situation that lreads to colour steps is illustrated
below
Notice the double edge to this petal. This problem is due to CZ
thinking the petals out of focus image on another frame is detail.
You can take a threefold strategy hear: first select less false detail by
increasing the Detail parameter; second second make the transition from
one Frame to the next smoother by Lowpass Filtering the Depthmap; third to
take advantage of the smoothe transition you must us Interpolated
Output. You can modify the Do Stack macro to do all of these
things. Here is the end result.
