Saving .png from render texture results in much darker image

Question

I wrote a script that saves a render texture to a .png.

However, the results are not very good, the .png is always much darker than the Render texture is in Unity. How can I fix this so that there is no attempt at color correction?

Script:

 [SerializeField]
     RenderTexture rt;
 
     [SerializeField]
     string fileName;
 
     [Button("Save png")]
     public void SavePNG()
     {
         var tex = new Texture2D(rt.width, rt.height);
         RenderTexture.active = rt;
         tex.ReadPixels(new Rect(0, 0, rt.width, rt.height), 0, 0);
         tex.Apply();
 
         var path = "Assets/Textures/Rendered textures/" + fileName + ".png";
         File.WriteAllBytes(path, tex.EncodeToPNG());
         Debug.Log("Saved file to: " + path);
     }

Answer 1

So I managed to get it working thanks to advice from DMGregory. Since sRGB is a readonly field, you have to create a rendertexture in code. Here is my full code:

[SerializeField]
RenderTexture rt;

[SerializeField]
Camera cam;

[SerializeField]
string fileName;

[Button("Save png")]
public void SavePNG()
{
    RenderTexture mRt = new RenderTexture(rt.width, rt.height, rt.depth, RenderTextureFormat.ARGB32, RenderTextureReadWrite.sRGB);
    mRt.antiAliasing = rt.antiAliasing;

    var tex = new Texture2D(mRt.width, mRt.height, TextureFormat.ARGB32, false);
    cam.targetTexture = mRt;
    cam.Render();
    RenderTexture.active = mRt;

    tex.ReadPixels(new Rect(0, 0, mRt.width, mRt.height), 0, 0);
    tex.Apply();

    var path = "Assets/Textures/Rendered textures/" + fileName + ".png";
    File.WriteAllBytes(path, tex.EncodeToPNG());
    Debug.Log("Saved file to: " + path);

    DestroyImmediate(tex);

    cam.targetTexture = rt;
    cam.Render();
    RenderTexture.active = rt;

    DestroyImmediate(mRt);
}

Answer 2

There are several possible reasons why this could occur. Here are a few.

1. Unity is displaying the real-time rendered image in a different color space then it uses when drawing the PNG, due to some internal color management quirk. If this is the case, DMGregory's comments should point you in the right direction.

2. Your operating system or image editor (it's not clear how you're viewing the PNG) uses a color profile that isn't applied to Unity. If you're on Windows 10, search for the "Color Management" utility and open it to see what color profile your PC is using (if any). If you're viewing the image in an image editing application such as Photoshop, check the application's color profile settings, and see if the image looks different when viewed with different software (e.g. Windows Photos vs Photoshop vs Paint)

3. Your video card drivers apply color correction settings that aren't the same between desktop and 3D. To determine this, you'll have to check your video card drivers.