Here are 2 gamma correction postprocess shaders you can try:
#define GAMMA 2.2
vec3 gamma(vec3 col, float g)
{
float i = 1. / g;
return vec3(pow(col.x, i)
, pow(col.y, i)
, pow(col.z, i));
}
fragData0.rgb=gamma(fragData0.rgb, GAMMA);
or the cheapest one, looks like the one above but with no adustments to gamma.
fragData0.rgb = sqrt(fragData0.rgb);