There are a number of ways to get around this problem, but the one that I am going to use here is to apply an inverse gamma correction to my texture maps, so that they are in the same space as the lighting to start with and when the gamma correction occurs they are put back to their original color value.
The first thing to do is to set the Gamma value in the mia_exposure_simple node back to 1.0.
Now I open up the Render Settings window and click on the Quality tab. I scroll to the bottom and find the Framebuffer rollout. When expanded, there is a Gamma option here too, so I set this value to the inverse of 2.2 (to "anti gamma correct" our color maps). 1 divided by 2.2 equals 0.4545, so I enter 0.455 and type that value in the Gamma option in the Framebuffer.
With that done I now have a linear workflow setup for the scene and will be able to correctly preview the output in the Render Viewer. At this stage, I can make a test render and compare it to the draft lighting from the block-out phase (Fig.14).
Tuning and Balancing the Lighting
There are a few areas in the scene that I can tweak to have a bit more artistic control over the lighting.
Firstly, there are the controls over the Sun and Sky system itself, which can be found in the Indirect Lighting tab in the Render Settings window. As well as increasing or decreasing the overall intensity with the Multiplier value, I can apply some color correction with the Red/Blue Shift and Saturation values. I play with these values to get a stronger sunlight with a bit more warmth.
Now I can take a closer look at the controls for the portal lights. First, I select one of the window area lights and in the Attribute Editor I click on the mia_portal_light tab.
I find portal Lights really useful when working with the Sun and Sky system as I can use the Intensity and Color multipliers to influence the lighting contribution of each individual window light. This allows for a more artistic way of managing the lighting as I use the multipliers to, for example, bias the brightness of the lighting to one side of the room, or to warm or cool certain areas.
For this scene, I make the main window carry a bit of extra brightness and warm up the light portal with an orange tint. I give the secondary window a cooler, light blue tint and change the Intensity multiplier to 1.000.
In terms of mood and color, the lighting now has the same general feel as the block-out did, but has a lot more sophistication and the appearance of realism.
Finishing Touches to the Light Scheme
Before I lock down the lighting and move on to the shaders, there are a few finishing touches that I want to make. Now that I have seen a pretty good preview of the final lighting, I decide I want to have a bit more bounce light in the room and am also a bit concerned that the foreground areas are a bit under-lit and uninteresting (Fig.15).
Normally, I'd deal with these kind of problems by adding a few extra spotlights and isolating them to the objects that need some extra lighting, but in this scene I take a different approach and cut some extra windows off-camera to provide the extra illumination.
For the foreground objects, I'd like to continue the look of using blinds to break up the sunlight that worked well elsewhere in the scene. Because the objects and lighting are already nicely composed, I want to work the lighting around the objects rather than the other way around. So I'll cut out a new window off-camera in just the right place to get some nice lighting on the foreground.
A trick I like to use for this is just to move and scale (not rotate) the directional light so that it is pointing where I'd like the light to fall. Then I look at where it intersects the wall and cut out a window there. I have the luxury of cheating with the size and placement of the window since it's never seen on camera for the render, so I can really use artistic license to get the light on the foreground exactly where I want it.
Once happy with the amount of light on the foreground, I add in some shadow casting geometry to give the appearance of blinds over the window that break up the light a bit.
Similarly, to allow more bounce light into the scene I cut another large window off-camera towards the back of the room, and add another area light and portal light combination. This is to add a little fill lighting to the room in general and also another bright source of reflection, which will be helpful for the shiny plastic and metallic shaders (Fig.16).