Tone Mapping (CineRender Effect)
This effect is available in the Detailed view of PhotoRendering Settings for the CineRender engine.
CineRender always renders internally using 32 bits. These color values must be interpreted in order to convert these to 8 or 16 bits for commonly-used output devices. This is done by a series of algorithms (operators) that use different methods.
Note that Tone Mapping permanently modifies the image. If you are planning to perform a color correction in another application (e.g., Photoshop, After Effects, Nuke, etc.) you don’t have to perform tone mapping in CineRender.
Save as TIFF
To get the full effect of Tone Mapping, you must save the Render in TIFF format, and adjust the Image Save Options to “High Accuracy Color with Alpha Channel.”
Operator for Tone Mapping
When choosing an Operator, it is best to test which one works best for the scene at hand.
Generally speaking, the Reinhard method is the most flexible method. It is based on photographic principles.
Operator: Linear Modes
The linear modes brighten or darken all regions of the image uniformly. This means that some image regions can be drowned out.
•Linear: This is a simple mode that multiplies all color values with the Scale factor. Both dark and bright regions will be brightened or darkened.
•Photo Linear: These common camera settings can be used to adjust the results.
–Exposure (the larger the value, the brighter)
–ISO (the larger the value, the brighter (this setting represents the film/sensor sensitivity)
–F-Stop (the larger the value, the darker)
–Gamma: Can be used to increase (larger values) or decrease (smaller values) the image’s mid-range brightness (which is actually not linear behavior if the value is not equal to 1).
•Auto Linear: This operator can be compared to a camera’s automatic exposure: an average brightness value for the image is determined internally. Based on this, correct values for Exposure and F-Stop will be defined, using Photo Linear formulas. Subsequently, a gamma correction can be made using the Gamma setting.
This option determines the brightest point and sets it to white. The remainder of the image will be “scaled” relative to this point. If there are very bright regions in the image, darker regions will be made much darker or even black.
The Reinhard operator is based on tone mapping techniques used in photography. As you can see in the image below, bright regions are compressed in particular. This tone mapping method is the most widely used method for rendering.
Pre-Scale primarily affects darker regions (higher values can be used to brighten shaded regions) and the Post-Scale is used to adjust brighter regions, and even blends between linear and exponential curve progression.
Three Reinhard curves with different Burn values from 1 to 3.
Tone Mapping Example
The following scene is rendered without Tone Mapping:
The luminous material at the left has a brightness of 250%, a sphere lies at the right in the dark.
As you can see, there are over-exposed and very dark regions.
The image below illustrates how some of the operators work. (Photo Linear is not used here because it behaves similarly to the other linear operators.)
As seen in the image, Auto Linear works best (in combination with Gamma): Very bright regions are darkened and dark regions are brightened. Reinhard doesn’t work very well with this scene: very dark regions cannot be brightened adequately. The Reinhard operator works best for scenes with even lighting and no very dark regions (e.g., interior room renderings).
The linear operators don’t work well with the example scene, because they either darken bright regions, which makes dark regions even darker, or they brighten dark regions, which over-exposes brighter regions.