Rendering

Creating HDR environment maps from a 3D scene

Generating a HDR environment from your 3d scene is in fact not that much different from how you would go about in real life. The two most common options are to either shoot a chrome ball or to use multiple images to construct a spherical panorama. While there are 3rd party plugin which enables you to render the scene trough a spherical lens, you can just as easily create a virtual chrome ball to serve your needs.

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Using render channels in Softimage

The typical use of render channels is to render the scenes components, such as ambience/diffuse, reflection or motion vectors into individual images. As most of these components are calculated individually by Mental Ray anyway they’re not going to affect the time needed to render the image. In addition, channels can be used to render partial or multiple render trees, adding ambient occlusion, outputting mattes or any other type of information within a single pass. In this case however, you won’t get them for free. 

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Expanding the width of the rendered image without distorting the camera perspective

By changing the cameras position and increase the size of the output resolution you’ll obviously be able to widen the shot. Unfortunately you’ll end up with a completely different perspective. By compensating the cameras field of view angle in relation to the added pixels the expanded images will line up exactly with the original image when superimposed. The procedure will work just as well if you need to reduce the size of the image.

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Rendering XXL Sized images

While the images for a typical brochure often are printed at a resolution of between 150 and 300 dots per inch (dpi) posters rarely exceeds 100dpi. Once you reach the size of billboards you’ll probably end up at a resolution less than 30dpi. With the above in mind you should have limit the need for extreme high resolution rendering, but there are situations when you do want the extra pixels. The central problem with large images is the amount of RAM needed. Not only do you need to cover the frame buffer/image itself which can easily grow to several hundred mega bytes (this is without considering the recourses need to actual compute the rendering) you also need to have this amount of free continuous memory.

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Cast Shadow Only Lights in XSI

Using two lights

While it may sound simple enough, it does require a little trick. By adding a light to the scene you’ll get the wanted shadow but you’ll also get the extra illumination. So you’ll need to create a second light that will remove the added illumination but leaves the shadow intact. Open the scene NegativeLight.scn from this issues CD.
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Custom Depth Pass in XSI

 

There are a couple of different ways to create depth passes in XSI, including the pre defined that can be found in the Render > Pass > Edit > New Pass menu. Since it’s only a mouse click away, it’s obviously the quickest to create. However, finding the proper values may not be the most intuitive with this setup.
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Studio Lighting

There’s a certain irony involved when people enquire about photorealism because, apart from the spelling, there isn’t really anything ‘real’ about it. What we perceive as being ‘realistic’ in an image (or an animation, for that matter) has more to do with whether it’s consistent with our expectations of it, rather than whether it’s truly representative of the real world. Over time, we get used to certain motifs being rendered in a certain way, and any deviation from this stands the risk of being regarded as strange or unnatural. As an extreme example, imagine Godzilla painted in vibrant pink and yellow stripes. No matter how good the paint job is, or how cute he looks, the effect would still look slightly odd, to say the least.

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