how to get original RGB values from shader to 3d render texture…?

Godot Version

4.2

Question

Hello,
I’m rendering a subviewport to a texture and then I use this texture for masking etc. for a 2d game…
however… when I for example feed 0.5 in my shader to the albedo-output I get something like 0.737 in my render texture… but I’d need the original RGB value to compare it to other values later along the line…
is there any way to render 3d with the original rgb values from the shader…?
thanks

PS:
I also tried to account for linear output by feeding pow(0.5, 2.2) into Albedo… but the result is too far off…

simple test-shader:

shader_type spatial;
render_mode unshaded;

void fragment() {

ALBEDO = vec3(0.5);

}