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Manipulating color mapping

From: SketchUp Rendering Using V-Ray

Video: Manipulating color mapping

Color, or tone, mapping is an internal process that VRay uses to map the color values needing to be shown in our rendered images. Particular focus is given to the brightest and darkest values inside of an image. Color mapping does actually have a number of similarities to a camera's exposure control or the responses of the human eye to light levels found in the environment, as V-Ray's color mapping has been designed to map the colors in our pixels to a range that is usable by, and/or viewable on, a computer display device.

Manipulating color mapping

Color, or tone, mapping is an internal process that VRay uses to map the color values needing to be shown in our rendered images. Particular focus is given to the brightest and darkest values inside of an image. Color mapping does actually have a number of similarities to a camera's exposure control or the responses of the human eye to light levels found in the environment, as V-Ray's color mapping has been designed to map the colors in our pixels to a range that is usable by, and/or viewable on, a computer display device.

Of course, color mapping in some form is something that all render engines do. Without a final translation of information collected from the scene to RGB color values, well, we would never get any images from our renders. One of the nice things about V-Ray, however, is that it allows us to make some prerendered choices as to just how we want this color mapping to work. To take a look at the Color Mapping options available in VRay, we need to open up the Options Editor and then come into the Color Mapping rollout. Here, as you can see, we have a number of controls that will affect how color mapping is working in our renders.

In this video, we just want to focus on the different color mapping types available to us. Each of these has been designed to deal with a particular color mapping problem. This means they each have their strengths, but naturally, that means they each have their own drawbacks as well. To examine how these color mapping types are working, we are once again going to make use of Adobe Photoshop to just make a comparison between a number of test renders. The only options we won't give any attention to are the Gamma Correction and Intensity Gamma types.

These really are just legacy options left over from the days when V-Ray didn't have a Gamma option available in each of the Color Mapping modes. As this is no longer the case, we can just ignore the Gamma Correction and Intensity Gamma options. So let's jump over into Photoshop then and see what our renders reveal. As we've already mentioned, the real focus of color mapping is really the brightest and darkest values found inside of a rendered image. It's not surprising, therefore, that when we switch between our renders, you can see that really, the biggest changes occur in those areas, particularly in the brightest values, or the brightest areas we find inside our rendered image.

That really is the big difference that you see between these Color Mapping modes. Linear Multiply is an excellent mode for using in a compositing workflow. The mathematics behind it are very straightforward and simple. The problem is, oftentimes we find extremely burned areas inside of an image that has bright light sources. Because of this, many users lean towards using the Exponential Color Mapping mode, which as you can see, does not suffer from that same burnout. If we just switch between the two, you can see there's quite a bit of difference between those color mapping modes.

The difference occurs because rather than multiplying samples as the Linear Multiply option does, this particular mode simply saturates a color based on the brightness of the samples taken. The problem is that whenever you increase the saturation of a color, you naturally push it towards white. As you can see, our bright areas are definitely pushing towards white values. If this is a problem for us, we may want to try the next of our Color Mapping modes, which is HSV exponential.

This, as you can see, works to preserve the color's hue and saturation, even in the bright areas. And as you can see, we definitely don't have that push towards white that exists inside of our Exponential render. The problem with this mode can be that the color preservation inside of those bright areas can look a little bit unnatural. Oftentimes they don't seem to balance with the brightness of the environment in which they are being rendered. If this is a problem for us, we may want to try Intensity Exponential instead, which as you can see, looks a little bit more natural in terms of how the bright areas are being mapped.

Again, this mode is similar to Exponential. In this case though, we preserve the ratio of the RGB color components, and only the intensity of the colors becomes affected. This means the falloff of the RGB intensity in our bright spots does look a little more natural. It behaves a little bit more as expected. This particular mode is in fact my personal favorite if I am not using the Linear Multiply option because of going into a compositing application. Now, our final render is taken from the Reinhard Color Mapping mode, which is in fact a hybrid of two existing color mapping modes in V-Ray.

This option actually gives us the ability to blend between a Linear Multiply and Exponential Type render, which oftentimes can be very useful indeed. We can still keep the brightness of a linear multiply image if that is what we want, but we can tone it down by just sliding things over towards an Exponential Render a little bit. The problem we have is that this appears to be a little bit broken in V-Ray for SketchUp at this moment in time. The parameter that controls that switch is the Burn value.

However, that appears to be missing inside our V-Ray for SketchUp's interface. No doubt, that will be corrected in future updates of V-Ray for SketchUp. Because then our use of the Color Mapping controls will affect not only the way our images look once they've been rendered, but also to some extent what we are able to do with our renders in post-production, it is really important that we start our V-Ray rendering sessions having made sensible color mapping choices. Now, that of course will depend entirely upon the needs of the project and the final deliverables required of us.

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This video is part of

Image for SketchUp Rendering Using V-Ray
SketchUp Rendering Using V-Ray

33 video lessons · 6185 viewers

Brian Bradley
Author

 
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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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