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C = 7/(2+12*sqrt(2)) = 0.3689927438004929
B = 6/(13+7*sqrt(2)) = 0.2620145123990142
first zero crossing = (45+14*sqrt(2))/(19+28*sqrt(2)) = 1.1058229337190195
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C = 7/(2+12*sqrt(2)) = 0.3689927438004929
B = 6/(13+7*sqrt(2)) = 0.2620145123990142
first zero crossing = (45+14*sqrt(2))/(19+28*sqrt(2)) = 1.1058229337190195
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C = 113/(58+216*sqrt(2)) = 0.31089212245300067
B = 12/(19+9*sqrt(2)) = 0.37821575509399866
first zero crossing = (123+36*sqrt(2))/(47+72*sqrt(2)) = 1.1685777620836932
If it's OK, I would like to add this one as a named filter, under the name "RobidouxSoft".NicolasRobidoux wrote:The above RobidouxSharp comes from minimizing the worst case deviation from the original value when the original value is one of the two extremes (0 and 255 in typical 8 bit).
An alternate way is to minimize the worst case deviation when the original value is the average of the largest and smallest possible values (for example, 127.5 in typical 8 bit). I will give this a try later.
It would not surprise me if this one lands almost on top of Mitchell-Netravali.
P.S. It's not. I should have remembered that minimizing the L^1 norm generally gives sparsity, and indeed the minimizer is the Keys cubic which is equal to 0 at sqrt(2):which, in principle, should be quite blurry.B = (9-3*sqrt(2))/7 = 0.67962275898295921
and
C = 0.1601886205085204
P.S. 2... and indeed it is pleasant, and very blurry:Code: Select all
convert rose: -define filter:c=.1601886205085204 -filter Cubic -distort Resize 3000% rose_RobidouxSoft.png
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convert rose: -colorspace XYZ -define filter:c=.1601886205085204 -filter Cubic -distort Resize 3000% -colorspace sRGB rose_RobidouxSoft.png
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Bartlett
Blackman
Bohman
Box
Catrom
Cosine
Cubic
Gaussian
Hamming
Hann
Hermite
Jinc
Kaiser
Lagrange
Lanczos
Lanczos2
Lanczos2Sharp
LanczosRadius
LanczosSharp
Mitchell
Parzen
Point
Quadratic
Robidoux
RobidouxSharp
Sinc
SincFast
Spline
Triangle
Welch
NicolasRobidoux wrote:Fred: I said I would add it, but have not done it yet. May take me a while.
I got the OK from magick to add RobidouxSoft and LanczosSharpest.