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10.8.5.2 Photographic tonemapper attributes

 
The photographic tonemapper converts actual pixel luminances (in candela per square meter) into image pixels as seen by a camera, applying camera-related parameters (like f-stops and shutter times) for the exposure, as well as applying tonemapping that emulates film- and camera-like effects.
 
Tonemapper sub-section in the Iray section of the camera Attribute Editor when Photographic is selected.
 
 
 
Tonemap Backplate
Enable this attribute to apply tonemapping to the image plane as well.
 
Film Iso
Film_Iso should be the ISO number of the film, also known as “film speed”.
 
Note:
cm2 Factor
 
Note:
This attribute change its behaviour dependent on the setting for the attribute Film ISO
 
 
Whitepoint
Whitepoint is a color that will be mapped to “white” on output, i.e. an incoming color of this hue/saturation will be mapped to grayscale, but its intensity will remain unchanged.
 
Camera Shutter
This is the camera shutter time expressed as fractional seconds. A value of 1 means 1 second, value of 100 defines a camera shutter of 1/100 and a value of 0.1 defines a camera shutter of 10 seconds. This value has no effect in “Arbitrary” mode.
 
f-Number
This is the fractional aperture number. For example, “11” defines aperture “f/11”. Aperture numbers on cameras go in a specific standard series: f/8, f/11, f/16, f/22, and so forth. Each of these are referred to as a “stop” (from the fact that aperture rings on real lenses tend to have physical “clicks” for these values) and each such “stop” represents halving the amount of light hitting the film per increased stop2. This value has no effect in “Arbitrary” mode.
 
Vignetting
In a real camera the angle with which the light hits the film impacts the exposure, causing the image to go darker around the edges. The vignetting parameter simulates this. At 0.0 it is disabled, higher values cause stronger darkening around the edges. Note that this effect is based on the cosine of the angle with which the light ray would hit the film plane, and is hence affected by the field-of-view of the camera, and will not work at all for orthographic renderings. A good default is 3.0, which is similar to what a compact camera would generate.
 
Note:
The parameters Crush Blacks and Burn Highlights guide the actual “tone mapping” process of the image, i.e., exactly how the high dynamic range values are adapted to fit into the black-to-white range of current display devices.
 
If Burn Highlights is set to one and Crush Blacks to zero, the transfer is linear, that is, the mapping behaves like a simple linear intensity scaler only.
 
Crush Blacks
When the upper part of the dynamic range becomes compressed it naturally loses some of it's former contrast, and one often desires to regain some “punch” in the image by using the Crush Blacks parameter. When 0, the lower intensity range is linear, but when raised towards 1, a strong “toe” region is added to the transfer curve so that low intensities get pushed more towards black, but in a gentle fashion.
 
Burn Highlights
Burn Highlights can be considered the parameter defining how much “over exposure” is allowed. As it is decreased from 1 towards 0, high intensities will be more and more “compressed” to lower intensities. When it is 0, the compression curve is asymptotic, i.e. an infinite input value maps to white output value, i.e. over-exposure is no longer possible. A good default value is 0.5.
 
Burn Highlights Per Component
Specifies how the Burn Highlights parameter is applied to the different color components. By default it is applied separately to all channels, which can lead to saturation loss though. Disabling the parameter applies the Burn Highlights to the luminance, keeping the output color as close as possible to the input color.
 
Saturation
Compressing bright color components inherently moves them towards a less saturated color. Sometimes, very strong compressions can leave the image in an unappealingly de-saturated state. The saturation parameter allows an artistic control over the final image saturation. 1.0 is the standard “unmodified” saturation, higher increases and lower decreases saturation.
 
Gamma
The gamma parameter applies a display gamma correction. If the image will be displayed as-is, without further post-processing by the application, this value should be set to match the displays characteristic, otherwise disabled by setting to 1.