Do gamma conversion manualy

Requesting sRGB capable framebuffer is unreliable

shaders/image.frag

@@ -4,9 +4,17 @@ uniform sampler2D qt_Texture0;
 uniform vec3 mtf_param;
 uniform bool bw;
 uniform bool invert;
+uniform bool srgb;
 in vec2 qt_TexCoord0;
 out vec4 color;
 
+vec3 Linear2sRGB(vec3 color)
+{
+    return mix(12.92 * color.rgb,
+               1.055 * pow(color, vec3(1.0 / 2.4)) - 0.055,
+               greaterThan(color, vec3(0.0031308)));
+}
+
 vec4 MTF(vec4 x, vec3 m)
 {
     x = (x - m.x) / (m.z - m.x);
@@ -22,6 +30,8 @@ void main(void)
 
     if(invert)color = vec4(1.0) - color;
 
+    if(srgb)color.rgb = Linear2sRGB(color.rgb);
+
     if(any(lessThan(qt_TexCoord0, vec2(0.0))) || any(greaterThan(qt_TexCoord0, vec2(1.0))))
         color = vec4(0.0, 0.0, 0.0, 1.0);