Default chroma option and range are wrong at smartblur filter

[nicol]

Summary of the bug: Default chroma option and range are wrong at smartblur filter.
How to reproduce:

% ffmpeg -h filter=smartblur
chroma_radius <float> ..FV.... set chroma radius (from -0.9 to 5) (default -0.9)
cr <float> ..FV.... set chroma radius (from -0.9 to 5) (default -0.9)
chroma_strength <float> ..FV.... set chroma strength (from -2 to 1) (default -2)
cs <float> ..FV.... set chroma strength (from -2 to 1) (default -2)
chroma_threshold <int> ..FV.... set chroma threshold (from -31 to 30) (default -31)
ct <int> ..FV.... set chroma threshold (from -31 to 30) (default -31)

https://ffmpeg.org/ffmpeg-filters.html#smartblur-1
chroma_radius, cr

    Set the chroma radius. The option value must be a float number in the range [0.1,5.0] that specifies the variance of the gaussian filter used to blur the image (slower if larger). Default value is 1.0. 

chroma_strength, cs

    Set the chroma strength. The option value must be a float number in the range [-1.0,1.0] that configures the blurring. A value included in [0.0,1.0] will blur the image whereas a value included in [-1.0,0.0] will sharpen the image. Default value is 1.0. 

chroma_threshold, ct

    Set the chroma threshold used as a coefficient to determine whether a pixel should be blurred or not. The option value must be an integer in the range [-30,30]. A value of 0 will filter all the image, a value included in [0,30] will filter flat areas and a value included in [-30,0] will filter edges. Default value is 0. 
ffmpeg version N-82785-g6b95da9
built on ... zeranoe

Patches should be submitted to the ffmpeg-devel mailing list and not this bug tracker.

[Carl Eugen Hoyos]

I tried to improve the documentation.
The smaller values are to ensure that chroma defaults to luma unless specified otherwise.