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Tutorials LightWave 3D Radiosity for Animation Qua Jan 26, 2011 3:10 am
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| by Marc Hemitte |
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| Radiosity looks cool but render time suffers.There are some cases where you can use it for animation without paying the heavy price. I loved the look of "a bug's life" and wanted to get a similar result for a job that involved a grasshopper. I found a way to achieve this result using the background only radiosity mode. Ok! Ready? 1) Create a gradient. You can use LightWave image viewer, an image editing software or Gradient thief from Kerlin software, a free utility. I'm going to show you both ways. [Tens de ter uma conta e sessão iniciada para poderes visualizar este link] a) With LightWave image viewer: Load your background plate in LightWave image editor. Double click on it to open the viewer. With the color picker (click-drag) take samples of your image, for instance top, middle and bottom. Make a note of the RBG values (top right corner). You'll operate the same way with any image editing software.  b) Using Gradient thief. Open Gradient thief ( assuming you downloaded and installed it first! ). Load the background image.  Delete the existing gradient leaving only one key in the middle and pick top, middle, bottom on your background image. (You can create more samples if necessary).Save the gradient.  2) LightWave layout. Load your scene .We've got several ways to skin our grasshopper:  a) Use the backdrop gradient to enter the RGB values you sampled previously.  b)Use the texture environment plugin to load the gradient we saved from Gradient thief (use z or x axis, planar proj.) or create your own with a gradient layer using the RGB values you noted before(on the pitch axis). <table align="center" border="0" height="71" width="79%"> <tr> <td>  </td><td>  </td></tr> </table> Use Viper to view the backdrop created. Don't worry if it doesn't look exactly like the gradient you created: viper take into account the camera angle and the top or bottom might not show completely.  The Gradient backdrop and the gradient layer in the texture environment give the best and slightly fastest result. You can activate or deactivate them in the tutorial scene file and see the difference by your shelf. You'll have to adjust the light and radiosity intensity every time. 3 - Open the light editor. I used a point light, but you can use any type you want . I like to disable specular, clone the light ,enable specular and disable diffuse on the spec light. This way, you get a better control .  Open the global illumination panel. Set ambient intensity between 0-5%. Check shading noise reduction. Enable radiosity, mode backdrop only. Adjust the intensity of your effect by balancing the influence of the diffuse light and the intensity of the radiosity. In this case, we'll set the radiosity to 300 % and the diffuse light to 150%, the scene happening outdoor in clear daylight. We'll have the spec light at 40%. Leave the ray number to default 4x12. You'll increase to taste when doing the final render.  4 - Enable ray traced shadows and make a test render. Adjust light and radiosity until you're happy.  5 - We need to cast a shadow on the ground. Uncheck unseen by camera under object properties , render tab. In the surface panel, under the ground surface, click on the color texture button. Choose front projection and load the background image we used to create the gradient. This way, the shadow color will match the background plate.  To only keep the shadow within the alpha channel, go to advanced tab and set the Alpha channel to shadow density.  Render the shadow as a separate pass, with no anti-aliasing and no radiosity. We'll blur it during the compositing process. When rendering the shadow pass, set the render option for the grasshopper to unseen by camera.  6 - Compositing. Once you rendered the radiosity pass of the grasshopper (3) in a format that supports alpha channel (tga 32 for instance) and the shadow pass (2), let's load the two sequences plus the background image (1).  You'll need to apply some blur on the shadow and reduce the opacity of the layer to match the intensity of the background image's shadows. I won't cover this topic further, as it disserve a full tutorial on its own.. In summary, where ever you want to use a background plate/image to light your object, creating a gradient from the original picture will save you a loooot of rendering time. You can try G-mill (surface shader) as well in place of Radiosity. I hope you enjoyed this tutorial (I guess so if you did read up to that point) and you can e-mail me any question or comment at: [Tens de ter uma conta e sessão iniciada para poderes visualizar este link] Download the Source Files Here |
