Unity code to save camera view to PNG image.

unity_save_camera_image.cs

    void Save_camera_image(Camera cam, string path){

        // set render target to target texture
        var currentRT = RenderTexture.active;
        RenderTexture.active = cam.targetTexture;

        // Make a new texture and read the active Render Texture into it.
        Texture2D image = new Texture2D(cam.targetTexture.width, cam.targetTexture.height);
        image.ReadPixels(new Rect(0, 0, cam.targetTexture.width, cam.targetTexture.height), 0, 0);
        image.Apply();

        // encode to PNG
        byte[] _bytes = texture.EncodeToPNG();

        // save file
        System.IO.File.WriteAllBytes(path, _bytes);

        // set render texture back to default
        RenderTexture.active = currentRT;
    }

byte[] _bytes = texture.EncodeToPNG();

texture is null ref.