// Recolours the picture by brightness with a smooth colour ramp.
// order 10
// slider amount 0.0 1.0 0.8
// slider palette 0.0 1.0 0.0
// slider contrast 0.5 3.0 1.2
float4 effect(float2 uv, Inputs in) {
    float3 c = in.image.sample(in.smp, uv).rgb;
    float luma = pow(dot(c, float3(0.299, 0.587, 0.114)), in.p.contrast);
    float3 ramp = 0.5 + 0.5 * cos(6.2832 * (luma * 0.8 + in.p.palette + float3(0.55, 0.4, 0.2)));
    float3 mapped = ramp * (0.15 + 0.85 * luma);
    return float4(mix(c, mapped, in.p.amount), 1.0);
}