Optimal sharpening strength (according to objective metrics) - 0.5. Can be applied only to luma channel (change OUTPUT to LUMA). To use it on-demand add the following line to input.conf: n change-list glsl-shaders toggle "~~/adaptive-sharpen.glsl"

adaptive-sharpen.glsl

// Copyright (c) 2015-2021, bacondither
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions
// are met:
// 1. Redistributions of source code must retain the above copyright
//    notice, this list of conditions and the following disclaimer
//    in this position and unchanged.
// 2. Redistributions in binary form must reproduce the above copyright
//    notice, this list of conditions and the following disclaimer in the
//    documentation and/or other materials provided with the distribution.
//
// THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR
// IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
// OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
// IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
// INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
// NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
// THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

// Adaptive sharpen - version 2021-10-17
// Tuned for use post-resize

//!HOOK OUTPUT
//!BIND HOOKED
//!DESC adaptive-sharpen

//--------------------------------------- Settings ------------------------------------------------

#define curve_height    1.0                  // Main control of sharpening strength [>0]
                                             // 0.3 <-> 2.0 is a reasonable range of values

#define overshoot_ctrl  false                // Allow for higher overshoot if the current edge pixel
                                             // is surrounded by similar edge pixels

// Defined values under this row are "optimal" DO NOT CHANGE IF YOU DO NOT KNOW WHAT YOU ARE DOING!

#define curveslope      0.5                  // Sharpening curve slope, high edge values

#define L_compr_low     0.167                // Light compression, default (0.167=~6x)
#define L_compr_high    0.334                // Light compression, surrounded by edges (0.334=~3x)

#define D_compr_low     0.250                // Dark compression, default (0.250=4x)
#define D_compr_high    0.500                // Dark compression, surrounded by edges (0.500=2x)

#define scale_lim       0.1                  // Abs max change before compression [>0.01]
#define scale_cs        0.056                // Compression slope above scale_lim

#define pm_p            1.0                  // Power mean p-value [>0-1.0]
//-------------------------------------------------------------------------------------------------

#define max4(a,b,c,d)  ( max(max(a, b), max(c, d)) )

// Soft if, fast linear approx
#define soft_if(a,b,c) ( sat((a + b + c + 0.056/2.5)/(maxedge + 0.03/2.5) - 0.85) )

// Soft limit, modified tanh approx
#define soft_lim(v,s)  ( sat(abs(v/s)*(27.0 + pow(v/s, 2.0))/(27.0 + 9.0*pow(v/s, 2.0)))*s )

// Weighted power mean
#define wpmean(a,b,w)  ( pow(w*pow(abs(a), pm_p) + abs(1.0-w)*pow(abs(b), pm_p), (1.0/pm_p)) )

// Get destination pixel values
#define get(x,y)       ( HOOKED_texOff(vec2(x, y)).rgb )
#define sat(x)         ( clamp(x, 0.0, 1.0) )
#define dxdy(val)      ( length(fwidth(val)) ) // =~1/2.5 hq edge without c_comp

#ifdef LUMA_tex
#define CtL(RGB)       RGB.x
#else
#define CtL(RGB)       ( sqrt(dot(sat(RGB)*sat(RGB), vec3(0.2126, 0.7152, 0.0722))) )
#endif

#define b_diff(pix)    ( (blur-luma[pix])*(blur-luma[pix]) )

vec4 hook() {

    // [                c22               ]
    // [           c24, c9,  c23          ]
    // [      c21, c1,  c2,  c3, c18      ]
    // [ c19, c10, c4,  c0,  c5, c11, c16 ]
    // [      c20, c6,  c7,  c8, c17      ]
    // [           c15, c12, c14          ]
    // [                c13               ]
    vec3 c[25] = vec3[](get( 0, 0), get(-1,-1), get( 0,-1), get( 1,-1), get(-1, 0),
                        get( 1, 0), get(-1, 1), get( 0, 1), get( 1, 1), get( 0,-2),
                        get(-2, 0), get( 2, 0), get( 0, 2), get( 0, 3), get( 1, 2),
                        get(-1, 2), get( 3, 0), get( 2, 1), get( 2,-1), get(-3, 0),
                        get(-2, 1), get(-2,-1), get( 0,-3), get( 1,-2), get(-1,-2));

    float e[13] = float[](dxdy(c[0]),  dxdy(c[1]),  dxdy(c[2]),  dxdy(c[3]),  dxdy(c[4]),
                          dxdy(c[5]),  dxdy(c[6]),  dxdy(c[7]),  dxdy(c[8]),  dxdy(c[9]),
                          dxdy(c[10]), dxdy(c[11]), dxdy(c[12]));

    // RGB to luma
    float luma[25] = float[](CtL(c[0]), CtL(c[1]), CtL(c[2]), CtL(c[3]), CtL(c[4]), CtL(c[5]), CtL(c[6]),
                             CtL(c[7]),  CtL(c[8]),  CtL(c[9]),  CtL(c[10]), CtL(c[11]), CtL(c[12]),
                             CtL(c[13]), CtL(c[14]), CtL(c[15]), CtL(c[16]), CtL(c[17]), CtL(c[18]),
                             CtL(c[19]), CtL(c[20]), CtL(c[21]), CtL(c[22]), CtL(c[23]), CtL(c[24]));

    float c0_Y = luma[0];

    // Blur, gauss 3x3
    float  blur   = (2.0 * (luma[2]+luma[4]+luma[5]+luma[7]) + (luma[1]+luma[3]+luma[6]+luma[8]) + 4.0 * luma[0]) / 16.0;

    // Contrast compression, center = 0.5
    float c_comp = sat(0.266666681f + 0.9*exp2(blur * blur * -7.4));

    // Edge detection
    // Relative matrix weights
    // [          1          ]
    // [      4,  5,  4      ]
    // [  1,  5,  6,  5,  1  ]
    // [      4,  5,  4      ]
    // [          1          ]
    float edge = ( 1.38*b_diff(0)
                 + 1.15*(b_diff(2) + b_diff(4) + b_diff(5) + b_diff(7))
                 + 0.92*(b_diff(1) + b_diff(3) + b_diff(6) + b_diff(8))
                 + 0.23*(b_diff(9) + b_diff(10) + b_diff(11) + b_diff(12)) ) * c_comp;

    vec2 cs = vec2(L_compr_low,  D_compr_low);

    if (overshoot_ctrl) {
        float maxedge = max4( max4(e[1],e[2],e[3],e[4]), max4(e[5],e[6],e[7],e[8]),
                              max4(e[9],e[10],e[11],e[12]), e[0] );

        // [          x          ]
        // [       z, x, w       ]
        // [    z, z, x, w, w    ]
        // [ y, y, y, 0, y, y, y ]
        // [    w, w, x, z, z    ]
        // [       w, x, z       ]
        // [          x          ]
        float sbe = soft_if(e[2],e[9], dxdy(c[22]))*soft_if(e[7],e[12],dxdy(c[13]))  // x dir
                  + soft_if(e[4],e[10],dxdy(c[19]))*soft_if(e[5],e[11],dxdy(c[16]))  // y dir
                  + soft_if(e[1],dxdy(c[24]),dxdy(c[21]))*soft_if(e[8],dxdy(c[14]),dxdy(c[17]))  // z dir
                  + soft_if(e[3],dxdy(c[23]),dxdy(c[18]))*soft_if(e[6],dxdy(c[20]),dxdy(c[15])); // w dir

        cs = mix(cs, vec2(L_compr_high, D_compr_high), sat(2.4002*sbe - 2.282));
    }

    // Precalculated default squared kernel weights
    const vec3 w1 = vec3(0.5,           1.0, 1.41421356237); // 0.25, 1.0, 2.0
    const vec3 w2 = vec3(0.86602540378, 1.0, 0.54772255751); // 0.75, 1.0, 0.3

    // Transition to a concave kernel if the center edge val is above thr
    vec3 dW = pow(mix( w1, w2, sat(2.4*edge - 0.82)), vec3(2.0));

    // Use lower weights for pixels in a more active area relative to center pixel area
    // This results in narrower and less visible overshoots around sharp edges
    float modif_e0 = 3.0 * e[0] + 0.02/2.5;

    float weights[12]  = float[](( min(modif_e0/e[1],  dW.y) ),
                                 ( dW.x ),
                                 ( min(modif_e0/e[3],  dW.y) ),
                                 ( dW.x ),
                                 ( dW.x ),
                                 ( min(modif_e0/e[6],  dW.y) ),
                                 ( dW.x ),
                                 ( min(modif_e0/e[8],  dW.y) ),
                                 ( min(modif_e0/e[9],  dW.z) ),
                                 ( min(modif_e0/e[10], dW.z) ),
                                 ( min(modif_e0/e[11], dW.z) ),
                                 ( min(modif_e0/e[12], dW.z) ));

    weights[0] = (max(max((weights[8]  + weights[9])/4.0,  weights[0]), 0.25) + weights[0])/2.0;
    weights[2] = (max(max((weights[8]  + weights[10])/4.0, weights[2]), 0.25) + weights[2])/2.0;
    weights[5] = (max(max((weights[9]  + weights[11])/4.0, weights[5]), 0.25) + weights[5])/2.0;
    weights[7] = (max(max((weights[10] + weights[11])/4.0, weights[7]), 0.25) + weights[7])/2.0;

    // Calculate the negative part of the laplace kernel and the low threshold weight
    float lowthrsum   = 0.0;
    float weightsum   = 0.0;
    float neg_laplace = 0.0;

    for (int pix = 0; pix < 12; ++pix)
    {
        float lowthr = sat((20.*4.5*c_comp*e[pix + 1] - 0.221));

        neg_laplace += luma[pix+1] * luma[pix+1] * weights[pix] * lowthr;
        weightsum   += weights[pix] * lowthr;
        lowthrsum   += lowthr / 12.0;
    }

    neg_laplace = sqrt(neg_laplace / weightsum);

    // Compute sharpening magnitude function
    float sharpen_val = curve_height/(curve_height*curveslope*edge + 0.625);

    // Calculate sharpening diff and scale
    float sharpdiff = (c0_Y - neg_laplace)*(lowthrsum*sharpen_val + 0.01);

    // Calculate local near min & max, partial sort
    float temp;

    for (int i1 = 0; i1 < 24; i1 += 2)
    {
        temp = luma[i1];
        luma[i1]   = min(luma[i1], luma[i1+1]);
        luma[i1+1] = max(temp, luma[i1+1]);
    }

    for (int i2 = 24; i2 > 0; i2 -= 2)
    {
        temp = luma[0];
        luma[0]    = min(luma[0], luma[i2]);
        luma[i2]   = max(temp, luma[i2]);

        temp = luma[24];
        luma[24] = max(luma[24], luma[i2-1]);
        luma[i2-1] = min(temp, luma[i2-1]);
    }

    float min_dist  = min(abs(luma[24] - c0_Y), abs(c0_Y - luma[0]));
    min_dist = min(min_dist, scale_lim*(1.0 - scale_cs) + min_dist*scale_cs);

    // Soft limited anti-ringing with tanh, wpmean to control compression slope
    sharpdiff = wpmean(max(sharpdiff, 0.0), soft_lim( max(sharpdiff, 0.0), min_dist ), cs.x )
              - wpmean(min(sharpdiff, 0.0), soft_lim( min(sharpdiff, 0.0), min_dist ), cs.y );
    
    float sharpdiff_lim = sat(c0_Y + sharpdiff) - c0_Y;
    /*float satmul = (c0_Y + max(sharpdiff_lim*0.9, sharpdiff_lim)*1.03 + 0.03)/(c0_Y + 0.03);
    vec3 res = c0_Y + sharpdiff_lim + (c[0] - c0_Y)*satmul;
    */
    return vec4(sharpdiff_lim + c[0], HOOKED_texOff(0).a);
}

Tried it on FineSharp and Anime4kDenoise and I found the same problem so it might be a general mpv gpu-next bug. Damn, I wish FineSharp worked fully with gpu-next. Also does anyone know if anti-ringing works on vo=gpu for polar downscaling and if anti-ringing works on vo=gpu-next for orthogonal downscaling? I've read that the latter doesn't work but I've only experienced the former but haven't read about it. This is using the latest chocolatey version of mpv