Last Pratt Class and a Different Way of Using a Background Image and mr Physical Sky | BIMuzer

Last Pratt Class and a Different Way of Using a Background Image and mr Physical Sky

This past Thursday night was my last class at Pratt for a while and, ironically, the same exact last question as last year was asked: how can I use the mr Physical Sky as well as a custom background image at the same time.  At the end of the last semester, I did some research and found a solution that seemed to work pretty well (  So, I tried it again and, oddly, it didn’t work.  So, I became somewhat obsessed and worked at this students file for two and a half hours.  During this time I found a good, three part tutorial on using the mr Physical Sky here: (the last three videos called Mental Ray Sky Part 1, 2 and 3).  The second video specifically mentioned that my method (he didn’t mention me by name), where you drag the mr Physical Sky into an empty slot in the Material Editor, click Use Custom Background Map and insert the image you want to use, is actually incorrect.  It’s really just, “placing one image over another,” and is, “blocking the sun,” “and your entire mental ray sky map.”  He says the reason for this is that the mr Physical Sky is what’s known as haze driven.  Unfortunately, his tutorial had a slightly different outcome than I was looking for in that, and hopefully I’m interpretting this right, he was using a high-contrast image of clouds to create clouds in the background and have it give off light.  So, I did some more research and came across another website (I love the Internet): (the guy who runs this site is one of the authors of Realistic Architectural Visualization Using 3ds Max and mental ray – I have the first edition, but the second edition is now out and available here).  In his article, he mentions a map that I’d never used (or really even heard of) before: Environment Background Switcher.  So, I modified my own method, some things I learned in the video, and his method to come up with a new method that appears to work.  Please note that the following is in 3ds Max Design 2011:

I have the following scene which has no lights, no Daylight System, no mr physical sky in the Environment Map, no Exposure Control Set, all mental ray settings are low and FG Bounces is set to 0:

  1. In 3ds Max 2011, the Command Panel can auto hide and I currently have that setting turned on.  Therefore, I hover my mouse over the Command Panel toolbar so it expands.
  2. Switch to the Top view and, on the Create tab, click the Systems icon: .
  3. Click the Daylight button and, when the Daylight System Creation dialog box appears asking if you want to turn on mr Photographic Exposure Control, click Yes.
  4. Click in the center of your structure and drag to out a bit to create the compass (in the past, I had placed the compass off to the side, but these tutorials suggested putting in the middle, so I did).
  5. When you let go of the mouse, a mental ray Sky dialog box will appear asking if you want to put the mr Physical Sky in the environment map.  Click Yes.
  6. Move your mouse a bit so the actual daylight system (which is made up of both the sun and sky objects) and then left-click to place it.  If you look on the Command Panel, the value of Orbital Scale was changing as you moved your mouse.  While this value needs to be a positive value, in the courseware I use in my class, it says that the value needs to be higher than your highest (or tallest) object.  Therefore, make sure it is.  I’ll set mine to 200 feet.
  7. Also, I’ll set the North Direction to 62 degrees.
  8. In step 5 the mr Physical Sky was put in the Environment Map.  We’re going to want to change that.  Therefore, open the new Slate Material Editor.  Since only a map can be place in the Environment Map, we can’t create a new material.  Within the center area, currently called View1, right-click, move your mouse over Maps, then mental ray, and then select Environment/Background Switcher:

  1. In the left column, the Material/Map Browser, click the group name Materials to collapse it.  Then, within the Maps group, scroll down and left-click and hold on Environment/Background Camera Map (I haven’t been able to find a simple explanation of what this map does so, if there’s anyone out there who can explain it, please email me).
  2. Drag and drop it on the gray circle to the left of Background (it will turn green):

  1. Scroll back up, left-click and hold on Bitmap and drag and drop it onto the gray circle next to the word Map of the new node:

  1. The Select Bitmap Image File dialog box will appear.  Find the background image you want and click Open.
  2. Click the Rendering pull-down menu and click Environment.
  3. Within the Common Parameters group, left-click and hold on the Environment Map (currently mr Physical Sky) and drag and drop it on the small gray circle (within the Slate Material Editor) next to Environment/Reflections on the first map (or node) you made.
  4. When the Instance (Copy) Map dialog box appears, click Copy and then OK.
  5. Back within the Environment and Effects dialog box, right-click the mr Physical Sky button and click Clear.
  6. Within the Material Editor, left-click and hold on the gray circle to the right of the original map (or node) you made and drag and drop it onto the None button, below Environment Map, within the Environment and Effects dialog box.
  7. When the Instance (Copy) Map dialog box appears, select Instance and click OK.
  8. We’ll need to adjust some settings on the background bitmap so, back within the Material Editor, double-click the Bitmap node to see it’s settings off to the right.
  9. Within the Coordinates group, select Eviron.  This sets the image as an environment map (ie. puts it in the background).  Since the image that we’re using is flat, as in, not a 360 degree image (usually hdri format), we’ll set the Mapping pull-down menu to Screen
  10. Since this image is very high resolution, in the Tile column, set both U and V to 1.75.
  11. If I were to render this now, you would see the edge of the background image and, therefore, see the image repeated.  To fix this, in the Offset column, set both U and V to .112 (I got to this value through trial, error and rendering).

If I were to render this right now, this is result:

  1. There’s light coming in from the exterior, but the Environment Map that we’ve create (ie. the background image), appears to be totally black.  The reason for this is that the Exposure Control settings is reducing the light that the image is supposed to be giving off.  Therefore, within the Exposure Control dialog box, with mr Photographic Exposure Control set, within the Physical Scale group, select Unitless and set the value to 100000.
  2. I’m also going to set the Exposure Value (EV) to 14.  This will lighten the image even more.

Now if I render, this is the result:

  1. At the bottom of the rendered frame window (or within the Render Setup dialog box), set the FG Bounces to 12 (again, I got to this value through trial, error and rendering).

Now if I render, this is the result:

The light still isn’t flowing far enough into the room.  We’ll use an mr Sky Portal which gathers sunlight towards it and aims it in whatever direction you choose.

  1. Switch to a Perspective view looking at the windows from the outside:

  1. Expand the Command Panel again and, on the Create tab, click the Lights symbol, , and select mr Sky Portal.
  2. Just above it, select the AutoGrid option.  This will let us place the sky portal right on top of the window.
  3. Left-click just outside the top-left of the window and drag down just outside the bottom-right of it.
  4. Once done, move the new mr Sky Portal slightly to the outside of the window.
  5. It’s important to note that the mr Sky Portal will also be effected by Exposure Control.  Therefore, on the Command Panel, set the Multiplier to 5 (this is yet another value I reached through trial, error and rendering.  You can also leave off the From “Outdoors” option which is used to have objects from behind the Sky Portal cast shadows.  This is the case for this model only because I know I don’t have anything modeled behind the Sky Portal).

If I were to render now, I’d get this:

Once I increase the following settings from below the Rendered Frame Window (the Global Quality Control Knobs), set the time of day to 5pm, the time of year to 4/30/2010, as well as increase the resolution to 2231 x 1275, I get the final rendered image below.

  • Image Precision (Antialiasing)Medium: Min 1/4, Max 4
  • Soft Shadows Precision – 0.5X – Medium
  • Final Gather Precision – Medium
  • Glossy Reflections Precision – 0.75X – Medium
  • Glossy Refractions Precision – 0.75X – Medium

This process definitely took some time to research and a lot of trial and error (and rendering) so I’d like to thank the various resources that I found on the Internet.  Let me know if you have any questions.