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Description
The Bitmap type Source Primitive uses an image file (*.jpg or *.bmp) to define the spatially varying power and chromatic characteristics of a source definition. Physical dimensions are applied to the Bitmap source and a user-supplied number of random rays are generated per pixel in the bitmap. The following algorithm is applied on a pixel-by-pixel basis in order to convert the bitmap image into a rayset:
1.A user-supplied number of rays have their starting positions randomized within each pixel
2.The chromaticity coordinates of the bitmap pixel are calculated
3.Given the user-supplied wavelengths, the weighting of each wavelength is determined using a color synthesis algorithm to match the chromaticity coordinates from (2)
4.The solved weighting factors from (3) are multiplied by any additional user-supplied weighting factors given in the wavelength list
Two methods of wavelength generation are allowed; Bitmap and List. When the Bitmap option is selected, FRED will automatically use three equally weighted wavelengths at 0.46, 0.54 and 0.62 microns. When the List option is used, the user may supply their own set of discrete wavelengths with customized weighting and the following rules apply:
•Fewer than 3 wavelengths: The weights of the wavelengths are given by the pixel's intensity (y-tristimulus) value, regardless of the wavelength
•Greater than 3 wavelengths: A color synthesis algorithm is applied to match the pixel's chromaticity coordinates (same as step 3 above)
For certain applications, the Bitmap wavelengths option may be insufficient to characterize the system's chromatic response. If, for example, the system contains spectral filters, then more than three wavelengths may be desired for raytracing and the user should consider using the List wavelength option.
Navigation
This feature can be accessed in the following ways:
•Menu > Create > Source Primitive > Bitmap
•Right mouse click on the Optical Sources folder, select Create New Source Primitive > Bitmap
•Toolbar button: .png)
Controls
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Control
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Inputs / Description
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Defaults
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Logical Parent
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Read-only. Specifies the source's parent node on the tree.
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Optical Sources
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Name
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Name of the source as it will appear on the tree view.
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Bitmap N
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Description
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Description string that will be visible on the tree view.
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Parameter Attributes
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0
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Specifies the total power of the source in units of Watts.
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1.0
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1
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The Select button allows the user to browse to a bitmap image (*.jpg or *.bmp). After selection, the dialog will update to show the selected file path and pixel count information.
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2
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Specifies the number of random starting ray positions within each pixel.
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1
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3
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Specifies the number of random ray directions emitting from each of the ray positions (parameter 2). The random directions are selected to lie within the angle cone defined by parameters 5-7.
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1
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4
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Specifies the semi-width of the bitmap along the X axis in document units.
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0.5
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5
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Specifies the semi-width of the bitmap along the Y axis in document units.
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0.5
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6
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Specifies the X semi-angle (degrees) of the cone of rays emitting from each ray position.
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90
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7
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Specifies the Y semi-angle (degrees) of the cone of rays emitting from each ray position.
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90
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8
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Specifies the shape of the emission cone (parameters 6 and 7). Can either be Ellipse/Circle or Rectangle/Square.
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Ellipse/Circle
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Wavelength Attributes
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Bitmap or List
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In the following descriptions, N is the number of ray positions in the source volume (parameter 2) and M is the number of ray directions emitting from each point (parameter 3).
When the Bitmap option is selected, FRED will automatically use three equally weighted wavelengths at 0.46, 0.54 and 0.62 microns. Three rays, one at each wavelength, will emit along the M directions leaving the N positions (i.e. the three rays all have the same starting ray direction).
When the List wavelength option is selected, one ray at each of the specified wavelengths will emit along the M directions leaving the N positions. The wavelength must have non-zero weighting after the color synthesis operation is performed.
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Bitmap
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Polarization
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Polarization
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If checked, polarization data for the rays is maintained and stored.
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Unchecked
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Handedness
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Sets the handedness of the polarization state (relevant for non-linear polarization states). If the ray is propagating towards you, the electric field vector rotates in a clockwise direction for Right handedness and counter-clockwise for Left handedness.
Note that for linear polarization, the application of Left or Right handedness is arbitrary. The user may find that the UI display switches handedness depending on the angle of the linear polarization state entered, but this will have no impact on the resulting representation of the linear state.
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Right
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Ellipticity
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Sets the ellipticity of the polarization state, 0 represents linear polarization and 1 represents circular.
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0
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Angle
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Sets the angle of the polarization relative to the X axis.
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90
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OK
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Accept settings and close dialog box.
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Cancel
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Discard settings and close dialog box.
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Apply
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Accept settings and keep dialog box open.
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Help
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Access this Help page.
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Related Topics
Plane Wave (incoherent)
Point Source (incoherent)
Lambertian Plane
Lambertian Surface
Rayfile Source
Random Volume into a sphere
Ray Fan
Solar Source (simple)
Laser Diode (incoherent)
LED (far-field)
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Copyright © Photon Engineering, LLC
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