uniform float factor; /// min:1 max:255 set:3

void mainImage( out vec4 fragColor, in vec2 fragCoord ) {
    vec2 uv = fragCoord.xy / iResolution.xy;
    vec4 src = texture(iChannel0, uv);
    fragColor = vec4(floor(src.rgb * factor + 0.5) / factor, src.a);
}