In addition to the below content, see also: Tone Mapping Operators at the Chaos Documentation Portal
The new Tone Mapping tools introduced in Corona 8 come with stackable operators that are applied from top to bottom.
Some operators, like Reinhard Highlight compression (formerly known as Highlight compression), and Filmic mapping (formerly known as Filmic highlights and Filmic shadows) are supported, and new operators were introduced as well.
Default Tone Mapping operators
The operators can be moved higher or lower by dragging and placing them. The highlighted line indicates where it will be placed once it is dropped:
The operators can be enabled or disabled as required:
New operators can be added by clicking the "plus" (+) button. You can add the same operator multiple times if needed:
To remove any operator, simply right-click on it and then click on the "Delete" option:
Ready-made presets can be used by clicking on the "Presets" button.
Note: that this will entirely remove the previous operator's setup/arrangement. <Currently, no undo/redo is available for Tone Mapping operators>:
Once you've found the right look for your image, you can save the tone mapping parameters by clicking the "Save..." button. This will create a ".conf" file that you can later load again by using the "Load..." button.
Note: Curves operator is only available within the Corona VFB. It is not present in Camera Tone Mapping override and for Global Tone Mapping, as this operator needs frame buffer input to work. See also the tooltip:
Photographic exposure, related changes
The tone mapping is now more flexible than before, as it comes in a stack which the user can modify to meet their needs. This required a method for an adjustable stack with the potential of having other operators added in the future. Not only did this have to apply to the VFB and its controls, it also had to be possible to be stored on a per-camera basis so that each camera could have its own unique tone mapping, if desired. To make all those things possible, exposure became an option between Simple Exposure and Photographic Exposure. Photographic Exposure operator uses photographic settings from the camera or global tone mapping for F-Stop, ISO, Shutter Speed, etc.
Global Tone mapping with Photographic Exposure operator uses "Basic Photographic Settings"
The aim is to allow users much greater control in tone mapping, so they could achieve a wider range of results, and also store those on a per-camera basis so that there wasn't a separation between how the cameras and the VFB handle tone mapping. The changes in Tone mapping are so significant that we do have to end up changing some workflows in order for the new benefits to become possible.
Override in the camera
This determines whether the camera uses the Global Tone Mapping stack (which will be seen in the VFB for a Perspective or other view that has no camera, or for cameras that do not have Override enabled), or whether the Camera uses its own unique Tone Mapping stack.
Note: when a Camera uses the Override option and that Camera view is being rendered, the VFB displays the Camera's tone mapping stack. This allows the tone mapping to be adjusted directly in the VFB without having to use the optional "Edit" to adjust the controls in the Camera. You can try this by looking through a camera, starting IR, enabling the Override checkbox for that Camera, clicking Edit in the Camera to open its tone mapping stack for editing, adding or deleting an operator from the stack in the Camera, and note how that change is reflected in the stack shown in the VFB. Then disable the Override checkbox and note how the VFB then returns to the Global tone mapping.
ACES OT operator
One of the new operators - ACES OT (Output transform) - is in the tone mapping stack and enabled by default.
Examples of ACES OT on/off :
ACES OT enabled
ACES OT disabled
The full-size comparison is here.
Note that highlights and color information in them is better mapped with ACES OT enabled and the overall image balance is better.
You may also need to adjust the exposure and tones after enabling ACES OT to compensate for them in some cases.
Adobe Wide RGB and ACEScg color spaces
In Corona 8 and newer you can change the internal color space for rendering in the Development/Experimental Stuff tab in the Render settings window. This is the color space where all the rendering calculations are done.
Corona has been using the Adobe Wide RGB color space for a while, and it is the default color space. Starting from Corona 8, you have the option to choose also between ACEScg and other internal color spaces.
As both Adobe Wide RGB and ACEScg are wide color spaces, the difference in renders for these color spaces will be subtle.
See these comparisons below:
https://corona-renderer.com/comparer/d7mWXO - a slight color difference in highlights - Metals
https://corona-renderer.com/comparer/yq5KwP - a slight hue differences for volumetrics - Glasses
It's worth understanding that:
- ACES OT is a tone mapping operator in Corona which simulates the ACES tone mapping workflow as if you were working with it.
- ACEScg is a color space where the rendering calculations are taking place, just like Adobe Wide RGB, which has been used for years by default.
As you can see, ACES OT can be used without any connection to ACEScg color space; still, you'll be able to get amazing results as well.