[FFmpeg-user] Documentation of chromanr filter

[Michael Koch]

Hello,

The documentation of the new chromanr filter, especially this sentence 
for the "thres" option is hard to understand:

"Sum of absolute difference of U and V pixel components or current pixel 
and neighbour pixels lower than this threshold will be used in averaging."

First of all I think "or" is a typo and should be "of". But even with 
this change the sentence is still hard to understand.
The sum of absolute differences of what? Sum of absolute differences of 
the U and V pixel components? That makes no sense.

This is how I think it might work:
Foreach neighbour pixel
{
   A = absolute difference of U components of current pixel and 
neighbour pixel
   B = absolute difference of V components of current pixel and 
neighbour pixel
   if (A+B < threshold) then
     use this neighbour pixel for averaging
}

If the above is correct, I suggest to change the sentence as follows:

"The algorithm calculates the absolute difference of the U components of 
the current pixel and a neighbour pixel. The same is also calculated for 
the V components. A neighbour pixel is used for averaging, if the sum of 
both absolute differences is lower than the threshold."

Also the meaning of  "stepw" and "steph" options is unclear:
-- Do these options refer to the pixels? If stepw=2 and steph=2 then 
only a quarter of the pixels is analyzed, and the same U and V 
components are used for 4 pixels?
-- Or do they refer to the selection of the neighbour pixels? If stepw=2 
and steph=2 then only a quarter of the neighbour pixels is analyzed?

Michael