Filtering out texture artifacts

I am currently encountering consistent artifacts in one of my shaders, which I’m using to generate a displacement map:

What is a common approach for filtering out these kinds of artifacts? I could imagine using a kernel to do some kind of lowpass, but is there anything obvious in my shader that might be causing this?

``````//	Simplex 3D Noise
//	by Ian McEwan, Ashima Arts
//
vec4 permute(vec4 x){return mod(((x*34.0)+1.0)*x, 289.0);}
vec4 taylorInvSqrt(vec4 r){return 1.79284291400159 - 0.85373472095314 * r;}

float snoise(vec3 v){
const vec2  C = vec2(1.0/6.0, 1.0/3.0) ;
const vec4  D = vec4(0.0, 0.5, 1.0, 2.0);

// First corner
vec3 i  = floor(v + dot(v, C.yyy) );
vec3 x0 =   v - i + dot(i, C.xxx) ;

// Other corners
vec3 g = step(x0.yzx, x0.xyz);
vec3 l = 1.0 - g;
vec3 i1 = min( g.xyz, l.zxy );
vec3 i2 = max( g.xyz, l.zxy );

//  x0 = x0 - 0. + 0.0 * C
vec3 x1 = x0 - i1 + 1.0 * C.xxx;
vec3 x2 = x0 - i2 + 2.0 * C.xxx;
vec3 x3 = x0 - 1. + 3.0 * C.xxx;

// Permutations
i = mod(i, 289.0 );
vec4 p = permute( permute( permute(
i.z + vec4(0.0, i1.z, i2.z, 1.0 ))
+ i.y + vec4(0.0, i1.y, i2.y, 1.0 ))
+ i.x + vec4(0.0, i1.x, i2.x, 1.0 ));

// ( N*N points uniformly over a square, mapped onto an octahedron.)
float n_ = 1.0/7.0; // N=7
vec3  ns = n_ * D.wyz - D.xzx;

vec4 j = p - 49.0 * floor(p * ns.z *ns.z);  //  mod(p,N*N)

vec4 x_ = floor(j * ns.z);
vec4 y_ = floor(j - 7.0 * x_ );    // mod(j,N)

vec4 x = x_ *ns.x + ns.yyyy;
vec4 y = y_ *ns.x + ns.yyyy;
vec4 h = 1.0 - abs(x) - abs(y);

vec4 b0 = vec4( x.xy, y.xy );
vec4 b1 = vec4( x.zw, y.zw );

vec4 s0 = floor(b0)*2.0 + 1.0;
vec4 s1 = floor(b1)*2.0 + 1.0;
vec4 sh = -step(h, vec4(0.0));

vec4 a0 = b0.xzyw + s0.xzyw*sh.xxyy ;
vec4 a1 = b1.xzyw + s1.xzyw*sh.zzww ;

vec3 p0 = vec3(a0.xy,h.x);
vec3 p1 = vec3(a0.zw,h.y);
vec3 p2 = vec3(a1.xy,h.z);
vec3 p3 = vec3(a1.zw,h.w);

vec4 norm = taylorInvSqrt(vec4(dot(p0,p0), dot(p1,p1), dot(p2, p2), dot(p3,p3)));
p0 *= norm.x;
p1 *= norm.y;
p2 *= norm.z;
p3 *= norm.w;

// Mix final noise value
vec4 m = max(0.6 - vec4(dot(x0,x0), dot(x1,x1), dot(x2,x2), dot(x3,x3)), 0.0);
m = m * m;
return 42.0 * dot( m*m, vec4( dot(p0,x0), dot(p1,x1),
dot(p2,x2), dot(p3,x3) ) );
}

varying vec2 vUv;
varying vec3 vPosition;

uniform sampler2D tDiffuse;

uniform float s_x;
uniform float s_y;
uniform float s_z;
uniform float map_min;
uniform float map_max;

float fbm(vec3 x) {
float v = 0.0;
float a = 0.5;
vec3 shift = vec3(100);
for (int i = 0; i < NUM_OCTAVES; ++i) {
v += a * snoise(x);
x = x * 2.0 + shift;
a *= 0.5;
}
return v;
}

float map(float value, float min1, float max1, float min2, float max2) {
return min2 + (value - min1) * (max2 - min2) / (max1 - min1);
}

void main() {
vec4 src = texture2D(tDiffuse, vUv);

vec3 scalar = vec3(s_x,s_y,s_z);
float n = fbm(src.rgb * scalar);

float c = map(n, -1.0, 1.0, map_min, map_max);
gl_FragColor = vec4(c, c, c, 1.0);
}``````

I’ve used this simplex noise function lots of times, and have never run into problems with its output. It’s always within the `[-1, 1]` range. The problem could be occurring in whatever data `tDiffuse` has, or inside `fbm()` or `map()` I can’t just read where the problem is taking place without a live example. Also, there are a lot of uniforms and constants that are being declared out of view from the code you provided. Maybe you can give us a live http://jsfiddle.net/ link to better help you.

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