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SketchUp Rendering Using V-Ray
Illustration by Richard Downs

Understanding the Exposure controls


From:

SketchUp Rendering Using V-Ray

with Brian Bradley

Video: Understanding the Exposure controls

In the real world, photographers use exposure to control the brightness of their photographic images. This means they can create images that not only look technically correct, but that are also able to evoke a response from their viewers. In chapter 2 of this course we looked at how the V-Ray Sun and Sky combined to create a physically accurate daylight simulation. As they are designed to create the same level of illumination as the actual sun and sky, they are, in layman's terms, extremely bright.
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  1. 4m 30s
    1. Welcome
      1m 14s
    2. What you should know before watching this course
      2m 33s
    3. Using the exercise files
      43s
  2. 7m 52s
    1. Installing V-Ray
      2m 27s
    2. Locating V-Ray tools and features
      5m 25s
  3. 39m 2s
    1. Creating natural daylight with the V-Ray Sun and Sky
      7m 41s
    2. Using the Omni Light
      7m 9s
    3. Exploring the Rectangle Light
      6m 2s
    4. Exploring the Spotlight
      4m 37s
    5. Exploring the IES light type
      5m 0s
    6. Setting up image-based lighting
      8m 33s
  4. 29m 40s
    1. Working with irradiance mapping
      12m 8s
    2. Creating a light cache solution
      6m 14s
    3. Using the DMC engine
      11m 18s
  5. 23m 11s
    1. Overview of the physical cameras
      5m 16s
    2. Understanding the Exposure controls
      6m 23s
    3. Handling perspective correction
      3m 4s
    4. Setting up for a depth-of-field effect
      8m 28s
  6. 44m 59s
    1. Introduction to V-Ray-specific materials
      9m 41s
    2. Creating diffuse surfaces
      9m 44s
    3. Creating reflective surfaces
      8m 2s
    4. Creating refractive surfaces
      9m 53s
    5. Creating translucent surfaces
      7m 39s
  7. 44m 8s
    1. Using fixed-rate sampling
      10m 21s
    2. Working with the Adaptive DMC engine
      11m 48s
    3. Controlling the Adaptive Subdivision sampler
      10m 15s
    4. Exploring subdivs and the DMC Sampler controls
      5m 52s
    5. Manipulating color mapping
      5m 52s
  8. 33m 39s
    1. Adding displacement to materials
      10m 48s
    2. Using caustic lighting effects
      7m 37s
    3. Creating occlusion effects
      8m 13s
    4. Creating a non-photorealistic render (NPR) with the Toon material
      7m 1s
  9. 1m 21s
    1. What's next?
      1m 21s

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SketchUp Rendering Using V-Ray
3h 48m Intermediate Sep 21, 2012

Viewers: in countries Watching now:

Create highly realistic 3D architectural drawings with V-Ray, a popular third-party renderer for SketchUp. This course shows how to take a single scene with interior/exterior elements and add lights, move cameras, and enhance objects with translucent and reflective surfaces. Author Brian Bradley explains concepts like irradiance mapping, perspective correction, and fixed rate sampling, while showing how to leverage each of the V-Ray tools and its material and lighting types to achieve specific effects.

Topics include:
  • Installing V-Ray
  • Creating natural daylight with V-Ray Sun and Sky
  • Bouncing light around with irradiance mapping and light caches
  • Setting up a depth-of-field effect
  • Creating diffuse and reflective surfaces
  • Working with the Adaptive DMC engine
  • Manipulating color mapping
  • Adding caustic lighting and occlusion effects
Subjects:
Architecture Rendering CAD
Software:
SketchUp V-Ray
Author:
Brian Bradley

Understanding the Exposure controls

In the real world, photographers use exposure to control the brightness of their photographic images. This means they can create images that not only look technically correct, but that are also able to evoke a response from their viewers. In chapter 2 of this course we looked at how the V-Ray Sun and Sky combined to create a physically accurate daylight simulation. As they are designed to create the same level of illumination as the actual sun and sky, they are, in layman's terms, extremely bright.

In fact, if we were to render in V-Ray without the use of Exposure control, we would get an image that was essentially a whiteout. In fact, let's go into our Options Editor we can show you just what we mean by that statement. So let's come into our Camera rollout. Down here you can see we have an Exposure checkbox. If we disable that and then take a test render--let's just dismiss our options dialog-- you'll see exactly what we mean. In this instance, as you can see, we don't even need to let our render finish, so I can just left-mouse-click to get focus on my V-Ray Frame Buffer and then just use the Escape key to cancel our render.

Our GI pre-calculation shows us that really, we're not going to get anything usable out of this particular render. Clearly, use of exposure control is extremely important when we are rendering with a V-Ray Sun and Sky, or a daylight system in place. There are of course other ways we could handle our illumination levels in the scene. We could, for instance, go into our Options Editor and instead of coming into the Camera rollout, we could come in to the Environment rollout and come into our GI Color Map Slot.

If you remember, in here, we have a TexSky node with the SunLight enabled and we have lot of controls that allow us to alter the appearance of our sun and sky in the scene. One of those controls is of course this Intensity setting, which means we can essentially turn down the illumination coming from our sun. The problem is this will essentially break the physicality or the reality of this lighting system. If we want realistic light behavior from our environment lighting, if we want realistic light bounce in the scene, then we need to keep the physicality of the system intact.

That is why, more often than not, making use of the V-Ray Physical Camera's Exposure controls makes a much better choice. Now of course not everyone is going to be comfortable with the idea of using real-world camera controls to deal with illumination levels in a 3D render. For this reason then, we are just going to spend a few minutes examining each of the controls that make up our exposure triangles and just see if we can get a better idea of the role that they play. First off, we will take a look at our Shutter Speed control.

One important piece of information we need to keep in mind with regard to this control is that any values we set in here are fractions of a second. So at this moment in time our Shutter Speed is set to be 135th of a second. That really is a vital piece of information. Now the shutter speed determines how long the shutter on our virtual camera will stay open. As with a real camera, lower numbers mean a slower shutter speed, as they represent a larger fraction of a second.

Now, that can take a little bit of thinking about, just to wrap our heads around that, so we'll just go over that again. Lower numbers mean a slow shutter speed because they represent a larger fraction of a second. Now slower shutter speed of course means that is more time for light to enter into a virtual camera. More light getting in means that over images will ultimately be brighter. The inverse is also true. Higher values placed inside of this field represent a small fraction of a second.

That means we have less time for light to enter the camera because we have a faster shutter speed and so our final render will be somewhat darker. Bear in mind also, that our shutter speed will determine the level of motion blur that gets applied to our render if we have the Motion Blur feature enabled. Let's jump across then to our F Number control. Now the F Number, or F stop, handles the size, controls the size, of our virtual aperture. Again, the numbers can be slightly puzzling, particularly if we have no camera experience, as small F Numbers represent a larger aperture, a larger opening in our camera, which in turn allows more light in. That will in turn give us bright images.

Again, the inverse equation is at work. Larger values set in here will give us a smaller aperture, and a smaller aperture means less light into the camera, which results in a darkened image. As with the Shutter Speed, the F number also has all the duties that it performs inside of the V-Ray Physical Camera setup. It will handle our depth-of-field effects. It will determent the way a depth-of-field effect is working in our renders, again, if we have that particular feature enabled.

The final value in our exposure triangle is the Film Speed or ISO parameter. Now the Film Speed value is the only part of the exposure triangle that doesn't control any other critical effects in the scene, any other camera effects. This fact makes it probably the best choice to be used as a quick dial for exposure changes in the scene. Now, the fact that we can set any value in here that we like also add to its appeal. This of course is different from real-world cameras.

Oftentimes if we set high ISO values, the images can suffer from excessive noise problems. Thankfully, that is not a limitation. That is not a problem with the V-Ray Physical Camera. In the V-Ray Physical Camera then, we have a tool that has been designed to mimic the kind of controls and effects available to real-world photographers and camera operators. If we approach lighting in now scenes in a physically accurate manner and use the exposure controls available to us, we will most certainly be able to capture the desired lighting, the desired illumination results from, or in, our rendered images. And hopefully this very quick overview of the V-Ray Physical Camera's exposure controls can go some way towards helping us feel comfortable using this process.

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