FFmpeg: Ultimate film grain

ffmpeg film grain

ffmpeg -i "HD Splice 1080p No Grain.mkv" -i "HD Splice 1080p No Grain.mkv" -filter_complex "
        color=black:d=3006.57:s=3840x2160:r=24000/1001,
          geq=lum_expr=random(1)*256:cb=128:cr=128,
          deflate=threshold0=15,
          dilation=threshold0=10,
          eq=contrast=3,
          scale=1920x1080 [n];
    [0] eq=saturation=0,geq=lum='0.15*(182-abs(75-lum(X,Y)))':cb=128:cr=128 [o];
 [n][o] blend=c0_mode=multiply,negate [a];
        color=c=black:d=3006.57:s=1920x1080:r=24000/1001 [b];
 [1][a] alphamerge [c];
 [b][c] overlay,ass=Subs.ass"
       -c:a copy -c:v libx264 -tune grain -preset veryslow -crf 12 -y Output-1080p-Grain.mkv

My goal is simulated film grain that looks more like the real thing than just per-pixel noise.