Tone mapping changes the brightness and contrast of your image. It can be done at any stage during the render process. Changes to tone mapping will be applied immediately to the rendered image. Tone mapping is non-destructive, so you can play around with the different tone mapping settings without permanently effecting the rendered image. You may want to tone map your image using different settings, and press Save Image to save out several different images.
How it works: Indigo creates a high dynamic range (HDR) image as it renders, and during the tone mapping process this will be converted to a low dynamic range red, green and blue image that can be displayed on your computer monitor. When subsequently saving the image, the user can choose to either save the tone mapped image in JPG, PNG, TIFF or EXR format. Indigo also supports saving of the un-tone mapped HDR image in EXR format for external tone mapping.
Tone mapping method comparisons
Indigo has four different tone mapping techniques that you can choose from: Reinhard, Linear, Camera and Filmic. Here are some comparisons of the different methods, and their strengths and weaknesses, using example scenes from Zalevskiy and Zom-B respectively.
Note how the Camera tone mapping method gives the image a more photographic look with higher contrast and a slight colour tint.
Reinhard is the simplest to use, but once mastered, camera tone mapping can give a nice artistic feel to the renders.
The Filmic tone mapper does a good job with achieving a bright look without burning out the whites.
Linear
The simplest tone mapping method, linear depends on just a single number. Every pixel in the HDR image will be multiplied by this number.
Reinhard
Reinhard is a method based on a paper by Reinhard, Stark, Shirley and Ferwerda from the University of Utah. It is an easy to use tone mapping technique because it automatically adjusts to the amount of light in the scene. It can be tricky to get linear or camera tone mapping to look balanced in scenes where there is an extremely bright light source – the Reinhard method is a good choice for scenes like this.
The default Reinhard settings of prescale=6, postscale=1, burn=2 will give good results for most renders. If you want to adjust the Reinhard method, below is an approximate description of each parameter.
| Prescale | Similar to a contrast control, works by increasing the amount of light in the HDR buffer. |
| Postscale | Works like a brightness control, increases the absolute brightness of the image after it has been tone mapped. |
| Burn | Specifies the brightness that will be mapped to full white in the final image. Can be thought of as gamma control. |
Camera
Camera tone mapping simulates the working of a photographer's camera. You adjust the exposure and ISO settings as you would in a real camera to modify the tone mapping.
The parameters you modify are:
| ISO | The ISO number represents the speed of film that is used. The higher the ISO number, the more light will be collected in the HDR Image. In low light situations, a fast film should be used, such as ISO 1600, and in bright lighting situations, a slow film can be used, such as ISO 100. |
| EV | The exposure value can range from -20 to +20 and represents a correction factor that is applied to the collected light. The higher the EV, the brighter the final image will be. Increasing the EV by one will make the image twice as bright. |
The final parameter is the response function. This specifies the type of film or digital camera to emulate. Different films and cameras emphasise different colours. The response functions are taken from real cameras – for example the images below use Ektachrome 100CD film which is famous for being used by National Geographic in their older photos.
A good default for sunny well-lit scenes is an ISO of 200 and an EV of -5.0.
Here are previews of each of the Camera Response Functions
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Filmic
Like Linear, this tone mapper has only one control, scale, but it responds quite differently compared to Linear with significantly less contrast at high scale values. This makes it particularly suitable for creating bright images while (to an extent) preventing highlights to burn out.