Calculating a realistic image can take time, but there are several things to think about before you raytrace that can drastically reduce your raytrace time.
Number of Lights - Unlike a render view, which can support only a limited number of lights, a raytrace view can handle as many lights as you like. Leaving the lights on is the number one cause of slow raytracing.
Use the Adjust Lights dialog available in render or floor plan views to turn off any lights that are not important to your scene. Remember that most lights are `on' by default.
Radiosity Quality - For simple scenes, Low Quality Radiosity is usually sufficient. High Quality Radiosity is extremely time-consuming and only necessary for very complicated scenes where Low or Medium radiosity is not sufficient.
If your image is very large, or if you have complicated aspects such as grills or grates, you may want to try Medium radiosity. Always try Low radiosity first to see if you get the desired result.
Preview Your Raytrace - When you are setting up lighting for a scene, there is no need to raytrace a full-screen image. Try using a much smaller image size - such as 300x200 - that can give you the information you need to determine whether lighting is appropriate.
Image size is a significant factor in determining raytrace speed. Only raytrace your full image when you are certain that your scene lighting is correct.
It may be helpful to create a configuration for previews so you do not have to reset all the options each time. See "Raytrace Configurations".
Anti-Aliasing Level - Anti-aliasing works to smooth edges that otherwise would appear jagged. High-quality anti-aliasing is most useful when you are raytracing a smaller picture that contains a very complicated scene. If you are raytracing a very large picture, you probably only need low-quality anti-aliasing.
Bump Maps - Bump map calculation is time-consuming and should only be used as necessary.
Soft Shadows - Soft shadow calculation is time-consuming and should only be used as necessary. Only enable soft shadows for lights whose shadows are significant to the scene you are raytracing.
It is not hard to create an image that looks reasonably realistic with raytracing, but producing an image that really looks like a photograph takes extra attention to detail. Here are a few tips for achieving the most photo-realistic images possible:
Use Radiosity - Although slower, radiosity adds significant depth to the scene by simulating the way that light works in the real world. Radiosity is especially effective in scenes with a fair number of shadows.
Use Reflections - For outdoor scenes, ensure that your windows are slightly reflective. You may want to set up a building across the street that, though not in the scene, appears in the reflections in the windows. Especially important are partly reflective materials on objects such as stovetops, tile floors, and coffee pots. The subtle effect of the reflections help convince the viewer's eye that the picture is a real photograph.
Sunlight Settings - The brightness of the sun varies dramatically from climate to climate, from cloudy day to sunny day. Use the Direct/Diffuse Sunlight Settings to find a setting that provides the appropriate lighting for the scene you are rendering.
Lighting - Lighting is an extremely important tool for achieving high-quality results. Work with the lighting of your scene until you achieve something realistic.
Add 3D lights as necessary to capture the effect you want. For lights that cast shadows into the scene, consider soft shadows that smooth the appearance of the scene lighting. See "Added Lights".
Finally, from the raytrace window, use the File> Image Adjustment options to subtly adjust the brightness of your finished rendering. Don't be afraid to over-saturate your image slightly in very bright areas - this is a common occurrence in actual photographs.
Interior Shots - If you are raytracing an interior radiosity view where the primary source of light is the sun through a window or door, you probably need to adjust your image brightness using File> Image Adjustment in the raytrace window. You may also need to use Medium radiosity quality to ensure that the raytracer models the light bouncing through the window accurately.
Bump Maps - Though the effect of bump-maps are usually very subtle, they do add to the impression that the scene is actually a photograph. A tile floor that shades appropriately to the lighting in the room, for example, lends to an appearance of realism.
Emissive Materials - A material with emissive properties actually cast light into the scene when Radiosity is used. This effect can be used to achieve the subtle variations of light seen in the real world.
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