How can I thread this function?

I'm working on a light study using unity that uses the ray function in the physics engine to simulate light rays. I've got to the stage where I can render an image, but it freezes the program up for 20 seconds while it calculates the render. I tried running my render function in a new thread, but then I found out that nothing in Unity is thread safe other than doing 1+1 XD. (Joking)

Under the assumption that I don't care about super high frame rates or any performance issues, is there any way I can run this function in another thread without it complaining? I don't really know much about threads but I would have thought I could have some kind of a work around for this? Thanks

A snippet of code:

 function threadCamera() {
 
     var thread = new Thread(renderCamera);
     thread.Start();
 
 }
 
 function renderCamera() {
     t1 = Time.deltaTime;
     C.text = "COMPUTING";
     renderRes = float.Parse(renderResText.text);
     renderWidth = int.Parse(widthInput.text);
     renderHeight = int.Parse(heightInput.text);
     renderTexture = new Texture2D(renderWidth, renderHeight, TextureFormat.RGB24, false);
     blendFac = 0.5;
     bFacText.text = "bFac = " + blendFac.ToString();
     mCam.Render();
     //emitFac = Color.RGBToHSV(emitFac);
     for(var ii = 1; ii < renderHeight; ii ++) {
 
         for(var i = 1; i < renderWidth; i ++) {
 
             ray = Camera.main.ScreenPointToRay(Vector2((i / renderRes) + int.Parse(renderOffX.text), ((ii / renderRes) + int.Parse(renderOffY.text))));
             if(Physics.Raycast(ray, hit, 100)) {
                 tex = hit.transform.GetComponent.<Renderer>().material.mainTexture;
                 hit.transform.GetComponent.<Renderer>().material.EnableKeyword("_GLOSSINESS");
                 randfoc = 1 - hit.transform.GetComponent.<Renderer>().material.GetFloat("_Glossiness");
                 hit.transform.GetComponent.<Renderer>().material.EnableKeyword("_EMISSION");
                 emitFac = hit.transform.GetComponent.<Renderer>().material.GetColor("_EmissionColor");
                 pixelUV = hit.textureCoord;
                 pixelUV.x *= tex.width;
                 pixelUV.y *= tex.height;
                 difCol = (tex.GetPixel(pixelUV.x, pixelUV.y) + emitFac) / (randfoc + 2);
                 ray = Ray(hit.point, Vector3.Reflect(ray.direction, hit.normal) + Vector3(Random.Range(-randFoc,randFoc),Random.Range(-randFoc,randFoc),Random.Range(-randFoc,randFoc)));
                 if(Physics.Raycast(ray, hit, 100)) {
                     tex = hit.transform.GetComponent.<Renderer>().material.mainTexture;
                     randfoc = 1 - hit.transform.GetComponent.<Renderer>().material.GetFloat("_Glossiness");
                     emitFac = hit.transform.GetComponent.<Renderer>().material.GetColor("_EmissionColor");
                     pixelUV = hit.textureCoord;
                     pixelUV.x *= tex.width;
                     pixelUV.y *= tex.height;
                     difCol *= (tex.GetPixel(pixelUV.x, pixelUV.y) + emitFac) / (randfoc + 2);
                     renderTexture.SetPixel(i, ii, difCol);
                     ray = Ray(hit.point, Vector3.Reflect(ray.direction, hit.normal) + Vector3(Random.Range(-randFoc,randFoc),Random.Range(-randFoc,randFoc),Random.Range(-randFoc,randFoc)));
                     if(Physics.Raycast(ray, hit, 100)) {
                         tex = hit.transform.GetComponent.<Renderer>().material.mainTexture;
                         randfoc = 1 - hit.transform.GetComponent.<Renderer>().material.GetFloat("_Glossiness");
                         emitFac = hit.transform.GetComponent.<Renderer>().material.GetColor("_EmissionColor");
                         pixelUV = hit.textureCoord;
                         pixelUV.x *= tex.width;
                         pixelUV.y *= tex.height;
                         difCol *= (tex.GetPixel(pixelUV.x, pixelUV.y) + emitFac) / (randfoc + 2);
                         renderTexture.SetPixel(i, ii, difCol);
                         ray = Ray(hit.point, Vector3.Reflect(ray.direction, hit.normal) + Vector3(Random.Range(-randFoc,randFoc),Random.Range(-randFoc,randFoc),Random.Range(-randFoc,randFoc)));
                         if(Physics.Raycast(ray, hit, 100)) {
                             tex = hit.transform.GetComponent.<Renderer>().material.mainTexture;
                             randfoc = 1 - hit.transform.GetComponent.<Renderer>().material.GetFloat("_Glossiness");
                             emitFac = hit.transform.GetComponent.<Renderer>().material.GetColor("_EmissionColor");
                             pixelUV = hit.textureCoord;
                             pixelUV.x *= tex.width;
                             pixelUV.y *= tex.height;
                             difCol *= (tex.GetPixel(pixelUV.x, pixelUV.y) + emitFac) / (randfoc + 2);
                             renderTexture.SetPixel(i, ii, difCol);
                             ray = Ray(hit.point, Vector3.Reflect(ray.direction, hit.normal) + Vector3(Random.Range(-randFoc,randFoc),Random.Range(-randFoc,randFoc),Random.Range(-randFoc,randFoc)));
                             if(Physics.Raycast(ray, hit, 100)) {
                                 tex = hit.transform.GetComponent.<Renderer>().material.mainTexture;
                                 randfoc = 1 - hit.transform.GetComponent.<Renderer>().material.GetFloat("_Glossiness");
                                 emitFac = hit.transform.GetComponent.<Renderer>().material.GetColor("_EmissionColor");
                                 pixelUV = hit.textureCoord;
                                 pixelUV.x *= tex.width;
                                 pixelUV.y *= tex.height;
                                 difCol *= (tex.GetPixel(pixelUV.x, pixelUV.y) + emitFac) / (randfoc + 2);
                                 renderTexture.SetPixel(i, ii, difCol);
                             }
                             else {
                                 renderTexture.SetPixel(i, ii, difCol);
                             }
                         }
                         else {
                             renderTexture.SetPixel(i, ii, difCol);
                         }
                     }
                     else {
                         renderTexture.SetPixel(i, ii, difCol);
                     }
                 }
                 else {
                     renderTexture.SetPixel(i, ii, difCol);
                 }
             }
 
             else {
                 renderTexture.SetPixel(i, ii, Color.black);
             }
         }
 
     }
     i = 1;
     ii = 1;
     renderTexture.Apply();
     renderSprite = Sprite.Create(renderTexture, new Rect(0, 0, renderTexture.width, renderTexture.height), new Vector2(0.5f, 0.5f));
     spritePrev.GetComponent("Image").sprite = renderSprite;
     C.text = "NULL";
     t2 = Time.deltaTime;
     tText.text = (t2 - t1).ToString();
 }