|
|
|
| In the "Global Illumination - Photon Mapping"-box in the light dialog the parameters for the photon emission are entered.
|
|
|
| For a detailed introduction to photon mapping see:
|
| Photon Mapping - Introduction and examples
|
| Render Options - Global Illumination - Raytracing + Photon Mapping
|
| Material Dialog - Photon mapping object properties
|
|
|
| Each light source in CyberMotion can emit photons for the photon mapping process. However, you can also exclude individual light objects from this process. If you switch on the <No Photon Mapping for this Light Object> option in the light dialog, then, instead of emitting photons, the corresponding light object will illuminate the scene only with conventional direct light algorithms, no matter which rendering mode is activated. You can use this function for little lamps in instrument controls or for lights far away in the background or, e.g., for spot lamps illuminating only small parts of the scene. To save rendering time just switch on this function for all light objects that do not contribute much to the general illumination in the scene.
|
|
|
| Emit Photons from Both Sides of a Facet - This button is only applicable for area light objects. Area lights emit photons from all of the facets building the surface of the object. However, if the light object is formed from a closed shape, e.g. a sphere or a cube, it is not necessary to emit photons from the inner side of the light object. Therefore, as a standard, photons are emitted only in direction of the surface normals. (The surface normals of closed objects created in CyberMotion always show outwards).
|
| However, if you want to use open objects or flat surfaces without thickness as light objects, then simply switch on the <Emit Photons from Both Sides of a Facet>.
|
| Another possibility is to apply flat NURBS-patches for light panellings. To prevent the emission of superflous photons backwards into the walls, again switch off the emission of photons from both sides of a facet. With the menu function "View - Normals" you can include the depiction of normals in the viewport windows. Then, if the normals of a NURBS-patch are faced towards the wall, simply rotate the NURBS-panel by 180 degrees.
|
|
|
| Number of Photons - For each light source you can enter an individual number of photons to emit for the photon tracing. Numbers between 20,000 up to 10,000,000 are practical, depending on the complexity of the scene and the rendering mode. When applying a photon map only for indirect illumination then you can manage with relative small photon maps. To estimate the general area brightness in a small room you can do with photon maps of about 50,000 photons. However, if you apply photon mapping as a global illumination model without direct lighting then usually a million and more photons are needed to cover all details in the scene. Furthermore, you have to enter a corresponding high number of photons to gather for the photon pool to get smooth intensity transitions and to prevent a spotty appearance (about 600 up to 2500 and more, depending on the size of the photon map). This requires a fast cpu and a high memory capacity of at least 256mb and more.
|
|
|
| Intensity Correction - For each light source a light intensity can be entered via the "Light Intensity - Maximum Range" parameter. This light intensity fits best to the direct light algorithm that is used in conventional rendering modes but since photon mapping applies a totaly different illumination approach based on a more physical model, an intensity correction value is needed to match the light intensities when switching back and forth between simple raytracing and photon tracing. If you plan to render your scene with the photon mapping algorithm you ought to follow this course:
|
| Adjust the light intensities with normal raytracing for the preview renderings. Then render a first test picture in photon mapping mode. To balance the intensity variations in the picture caused by the two different illumination methods, adjust the light intensity for the photon emission via the intensity correction parameters instead of changing the general "Light Intensity - Maximum Range" parameter. Thus you can switch back to raytracing mode for faster previews when extending and editing your scene and light settings and in the end you can turn again to photon tracing without having to adjust again the light intensities for the photon mapping process.
|
|
|
| Caustics are light reflecions from highly specular surfaces or, e.g., the light gathered in a focal point after transmission through a glass lense.
|
|
|
|
| Example for caustic light reflections beneath a little glass figurine, caused by photons that were refracted when transmitting through the glass. The corresponding project file is part of the CyberMotion installation under "/projects/caustics/ant.cmo".
|
|
|
| Caustics Photons are stored in a separate Photon Map, the so-called Caustics Map:
|
| Usually a photon map is evaluated only for the indirect illumination in combination with direct light for the main illumination and shadow calculations. For this purpose it will do to emit only several ten thousands of photons into the scene so we can average the general area brightness at each point in the scene. Caustic reflections, on the other hand, are often sharp outlined light patterns, like in our figurine picture shown above. It would be impossible to render these light reflections when only a few photons had been scattered around - you wouldn't even see a glimpse of the light focused beneath the figurine. Now, it would be also ridiculous to emit millions of photons into the scene and having to evaluate huge photon maps afterwards, only to cover the light reflections of a little specular object somewhere in the scene. That's why we have to manage to different photon maps, one for the global photon map and the general illumination, and one separate caustic map only for those photons that have been reflected or transmitted via a specular surface before hitting a diffuse surface. The caustic map is build in a second photon tracing pass where additional caustic photons are aimed only towards such objects, that are highly specular or transparent and own the material attribute <Caustics - Aim Additional Photons at Object>. The evaluation of the two different photon maps requires also separate photon pools. For the global photon pool much more photons have to be gathered for the averaging process, so that soft and clean light transitions can be calculated for the area brightness. However, for the caustics pool we need comparatively fewer photons, because we want sharp and clearly visible light reflections.
|
|
|
| The caustics parameters in the light dialog:
|
|
|
| Caustics - Aim additional photons at objects that cast caustic reflections - The emission of additional caustic photons can be switched on or off for each light object separately. You should activate the caustic photon emission only for lights that stand nearby or are directed towards objects, that own the object attribute <Caustics - Aim Additional Photons at Object>. If you want to render a picture with the camera focused on a caustics object as the main part of the image, it is advisable to use a spot lamp for the illumination because then the stream of photons can be aimed directly towards the target object.
|
|
|
| n-Times more Photons - Determines the multiple of additionaly emitted photons to create the caustics effect. Instead of specifying a certain number of photons this time you just have to enter a factor that describes how much more photons per area have to be emitted towards the caustic objects than for the global photons. Take again the glass figurine as an example. The emission of global photons was set to 50,000 photons. For the emission of caustic photons the factor was set to the maximum value of 100 via the <n-Times more Photons>-Parameter. During the processing of the photon map in the first pass, when the 50,000 global photons are emitted, about 1100 photons found their way through the glass figure and were saved in the caustic map. Then the additional emission of caustic photons is started with 100-times more photons, this is 100 * 50,000 = 5 millions photons. But this is only a fictitious value that only specifies how much more photons per area are emitted in general. Since caustic photons are only directed towards caustic objects in the end "only" 200,000 photons find their way into the caustics map. This is more than enough for a sharp representation of the caustic light effects under the glass figure.
|