, I discuss the use of a "sigmoidal" colourspace to reduce halo and blur when upsampling with the classical Lanczos (tensor Sinc-windowed Sinc) 3-lobe filter. In this post, I briefly discuss using sigmoidization with EWA (Elliptical Weighted Averaging) LanczosSharp, that is, Jinc-windowed Jinc 3-lobe with filter support scaled so that the first zero crossing is pretty much where it should be when the image is a 1D impulse (pixel-wide white column on a black background).
EWA LanczosSharp is a really good low pass filter. Not as sharp as orthogonal Lanczos, but "cleaner".
Unlike what I did with orthogonal Lanczos, I will use a possibly slightly "unsafe" contrast value, namely the one that gives an enlarged black square that stays within 2.3 JND of black, when the square is on a white background. With LanczosSharp, the corresponding contrast value is about 12.09375
. (Maybe this value is slightly on the high side? This method is too new for me to know for sure.)
Code: Select all
magick INPUT.IMG -colorspace RGB +sigmoidal-contrast 12.09375 -filter Lanczossharp -distort Resize 400% -sigmoidal-contrast 12.09375 -colorspace sRGB OUTPUT.IMG
First, I'll repeat the four comparative tests based on http://www.wisdom.weizmann.ac.il/~visio ... ageSR.html
. (Note that I have absolutely nothing to do with this site or the methods tested therein.) I'll also add an enlargement of text which I put together myself (with GIMP).