The Bitmap ray positions specification uses a *.jpg or *.bmp file as a source grid for ray emission and weighting. This source specification is valid only for visible wavelengths. Creation of the source grid proceeds in the following way:
The following conditions are applied depending on the number of wavelengths being used: •Fewer than 3 wavelengths: The wavelength weights are given by the pixel's intensity (y-tristimulus) value, regardless of the wavelength. •Greater than 3 wavelengths: Color synthesis is used to set the wavelength weights for the given pixel.
As an example, the source shown below was synthesized with 10 wavelengths spanning the visible.
This feature can be accessed by selecting Bitmap (points defined by bitmap pixels) as the ray position type on the Positions/Directions tab of a detailed source dialog box.
Source wavelengths are set on the Wavelengths tab of a detailed source dialog and can usually be specified by either a list of wavelengths or a spectrum. In the case of the bitmap source, the spectrum option is disabled when the Bitmap ray positions type is being used. Standard RGB wavelengths can be set in the wavelength list by right mouse clicking in the wavelength list spreadsheet and selecting "Set Standard Bitmap Wavelengths" from the list menu. Depending on the application, more than three wavelengths may be desirable. For example, will the rays be passing through a filter? Is the number of wavelengths specified sufficient to accurately represent passage through the filter?
As mentioned in Step 4 in the Description section, the wavelength weights are applied at the end of the pixel color synthesis process. If a true color image of the bitmap is desired, the wavelength weights should be set to 1. If additional scaling is desired, the wavelength weights should be modified.
Ray Positions - Hexagonal Plane Ray Positions - Read rays from a file Ray Positions - User-defined Rays
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