Request: add Blargg’s RGB preset to NTSC shader(s)

Syh · 30 May 2021 16:41

I actually don’t know, but apparently we do have access to the source code for it, just a matter of someone that’s not a smooth brain like me to figure out how to translate that into some shaders.

Syh · 30 May 2021 20:41

Side tangent, it would be kinda cool to have multiple tap levels built into some ntsc shaders, to change it on the fly. (Good chance it’ll cause some slowdown compared to not having a multiple tap options.)

TBH, I’d love someone to tackle an ntsc-suite in the same manner that guest had done with advanced, dogway has with grade, and HSM has done with his reflection suite.

ProfessorBraun · 30 May 2021 23:02

Thanks! It’s not what Blargg does but let’s say that at least from a sharpness perspective it looks close. The values I posted above are from an old post of Themaister. But it can be tweaked I suppose (sharper or softer). Or someone with the source code is gonna translate that like @Syh said.

hunterk · 31 May 2021 02:18

I know fuck-all about matlab, but the source for the scripts used to calculate the taps are located here:

github.com

libretro/common-shaders/blob/master/ntsc/shaders/filter_2phase.m

T = 5.6;
beta = 0.50;
tt = -32 : 32;

% Cosine windows reduce ringing artifacts.
cosine_window = cos(pi * beta * tt / T) ./ (1 - (2 * beta * tt).^2 / (T * T));

luma = (1 / T) * sinc(tt / T) .* cosine_window .* kaiser(65, 1.0)';

chroma = gausswin(65);
chroma = chroma / sum(chroma);

close all;
figure(1);
freqz(luma);

figure(2);
stem(luma);

figure(3);

This file has been truncated. show original

and https://github.com/libretro/common-shaders/blob/master/ntsc/shaders/filter_3phase.m

And there was an older set of taps for 3-phase that I liked for the effect it had on colors, though it was evidently less accurate for whatever reason, and you can find those taps here:

github.com

hizzlekizzle/quark-shaders/blob/master/NTSC.shader/ntsc-pass2.fs#L16



uniform sampler2D source[];
uniform vec4 sourceSize[];
uniform vec4 targetSize;

#define OLD_THREE_PHASE //options here include THREE_PHASE, TWO_PHASE or OLD_THREE_PHASE
#define GAMMA_CORRECTION //comment to disable gamma correction, usually because higan's gamma correction is enabled or you have another shader already doing it
#define CRT_GAMMA 2.5
#define DISPLAY_GAMMA 2.1

#if defined OLD_THREE_PHASE
#define TAPS 24
const float luma_filter[TAPS + 1] = float[TAPS + 1](
   -0.000071070,
   -0.000032816,
   0.000128784,
   0.000134711,
   -0.000226705,
   -0.000777988,
   -0.000997809,
   -0.000522802,

Syh · 31 May 2021 02:41

I’ll look it over like I have some semblance of an idea of what I’m reading XD.

Appreciate it, I really will look over it.

ProfessorBraun · 31 May 2021 20:11

I’ve found this that might interest you,look for md_ntsc_impl.h -md_ntsc.h etc

Edit:

Just tested,looks great too