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Harnessing tone mapping, exposure, and gamma

From: SketchUp Rendering Using Twilight

Video: Harnessing tone mapping, exposure, and gamma

Tone mapping is simply the modification of an image to control the representation of the brightest and darkest values found in the pixels. Oftentimes, tone mapping is used to achieve a particular look or style for a final image. To access Twilight's tone mapping controls, we need to open up the Render dialog. So, let's come up to the Twilight toolbar and click on the Open Twilight Render icon. Here, as you can see, we have a render of our scene. This was taken using the easy 10 preset, which of course is a progressive unbiased method.

Harnessing tone mapping, exposure, and gamma

Tone mapping is simply the modification of an image to control the representation of the brightest and darkest values found in the pixels. Oftentimes, tone mapping is used to achieve a particular look or style for a final image. To access Twilight's tone mapping controls, we need to open up the Render dialog. So, let's come up to the Twilight toolbar and click on the Open Twilight Render icon. Here, as you can see, we have a render of our scene. This was taken using the easy 10 preset, which of course is a progressive unbiased method.

If we select the Camera tab, you can see at the end of the bottom we have our Tone Mapping controls. If we take a look at the options in the dropdown, you can see we have three choices available to us. At this moment in time, the render you're looking at is making use of this first option, which is None. As the name suggested, this mode produces an as-is image. No alteration of pixel values is taking place. And of course, as you can see, we have no controls with which to effect any changes. What we see is what we get.

However, just so that we are clear on the importance of tone mapping, it has to be noted that a form of tone mapping has already taken place inside of the Twilight render engine, so as to produce the pixel values that we are seeing. We just don't have access to any extra controls. We can't make any alterations using this particular mode. The second choice available in our dropdown list, and the default in Twilight, is the Simple option. Now of course tone mapping or the filtering of our tone mapping inside of Twilight is a post render process.

This means that in order to use the different tone mapping filter types, we have no need to rerender our image. We can just simply switch to another tone mapping filter. So, when we switch to simple, you can see we do indeed make a big difference to the look of our pixel values. At this moment in time of course our Exposure level is blowing out our render, so let's drop this down to a value of 1, which will essentially return us to the same end result as our None option. From this point of course we can tweak our Exposure levels up or down, although we do need to be careful because it is very easy to ruin the look of our image by overdoing or underdoing our exposure levels.

So, as you can see, we can increase the brightness of our overall image, or indeed, we can drop our exposure level down and darken the image. We also, as you can see, have a Gamma Adjustment option available to us. This essentially allows us to change the contrast ratio in our image on the fly. It allows us to remap the midtones. So, let's just set this to a value of 2, and you can see we lose a lot of contrast in the image. We flattened midtones out quite a lot. And if we drop this down, you can see we do exactly the opposite.

We produce a much contrastier-looking image. The final of our tone mapping filter types is Linear. With this option we only have control over the brightest and darkest pixel values in the image. We don't have any ability to affect the midtones in a separate manner. Essentially, now the application will decide what is a bright pixel, what is a dark pixel, and as we make alterations to our values, it will be remap them accordingly. So, if we take our Brightness level and increase it, you can see, Twilight decides what a bright pixel is and will add to that.

If we take our Darkness level and decrease, you see Twilight will decide what constitutes a dark pixel and darken that down. Without tone mapping in some form, we wouldn't get any kind of usable images out of render engines. But with Twilight's simple and straightforward controls we do get a nice simple way to apply some measure of tone mapping to our images. However, if we want greater control over the mapping of pixel values in our renders, then perhaps our best option would be to render out of Twilight using the None Tone Mapping Filter type and then saving our renders out as floating-point images.

That way we can use the extensive tools available to us in postproduction applications such as Photoshop to really fine-tune and tweak our pixel values.

Show transcript

This video is part of

Image for SketchUp Rendering Using Twilight
SketchUp Rendering Using Twilight

33 video lessons · 4339 viewers

Brian Bradley
Author

 
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  1. 4m 1s
    1. Welcome
      1m 5s
    2. What you should know
      2m 10s
    3. Using the exercise files
      46s
  2. 6m 53s
    1. Installing the Twilight renderer
      2m 52s
    2. Locating Twilight tools and features
      4m 1s
  3. 50m 22s
    1. Adding the Physical Sun and Sky
      6m 17s
    2. Employing the Point light type
      6m 35s
    3. Using the Spot and Projector light types
      7m 7s
    4. Adding the IES light type
      3m 48s
    5. Using light-emitting materials
      6m 59s
    6. Creating image-based lighting using High Dynamic Range Images (HDRIs)
      6m 12s
    7. Using Sky Portals for interior global illumination (GI)
      6m 43s
    8. Understanding the importance of reflectance in materials
      6m 41s
  4. 21m 54s
    1. Exploring Light Transport options in Twilight
      9m 18s
    2. Managing the Quality presets
      5m 57s
    3. Editing and saving presets
      6m 39s
  5. 22m 8s
    1. Positioning your scene view
      3m 23s
    2. Altering projection types
      5m 12s
    3. Working with depth of field
      3m 59s
    4. Working with focal length
      2m 44s
    5. Harnessing tone mapping, exposure, and gamma
      3m 59s
    6. Using two-point perspective correction
      2m 51s
  6. 38m 13s
    1. Introduction to Twilight materials
      8m 23s
    2. Creating diffuse surfaces
      6m 53s
    3. Creating reflective surfaces
      6m 53s
    4. Creating glassy refractive surfaces
      9m 28s
    5. Creating watery refractive surfaces
      6m 36s
  7. 31m 28s
    1. Rendering for animation
      8m 55s
    2. Rendering out an alpha mask
      3m 44s
    3. Setting up a depth render
      4m 3s
    4. Creating an RGB mask using the Diffuse Texture Pass preset
      5m 45s
    5. Working with a composite
      9m 1s
  8. 1m 13s
    1. What's next?
      1m 13s

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