..::non photorealistic rendering::..

There are numerous plugins available for Max, which will produce such an image. This is normally done by the plugin changing the renderer and materials, but some will not let you to mix styles, or achieve a specific style that you are after. Another method is to apply an overall effect in Post; a Photoshop filter will normally do a quick but effective job, but, again, if you want to mix styles, then this is not the way to go.

You can, with some minor amendments here and there, create standard Max materials to produce an NPR effect. The most commonly used one would have to be a cellshade, but as this was covered in a Q&A back in issue 4, I’m not going to go into detail for this method, although I advise you look into a Gradient Ramp map, with Lighting type and Solid interpolation, mixed with a Falloff map set to Fresnel. Other effects can be generated similarly.

The general rule when designing materials for NPR is that nine out of ten times, there has to be actual shading on the rendered objects. The shading and shadow effect is generated by lighting; with shadows cast and various degrees of luminance (etc) from assigned materials. This is normally in the form of a graded shade or (almost) solid block colour for a shadow. Basically, what we need to do is to remove all block and graded shading from an object, then design the shading method ourselves. And the best way to do this is to crank the self-illumination up to 100%.

We shall look at producing a pencil sketch, mainly because in this style, shadows are not a solid colour, but vary in intensity due to the pressure of the ‘pencil’. So how do we produce this pencil effect? Easy… with a pencil. Three or four different intensities of shade should be produced, from very light to almost charcoal. These should then be scanned and tiled in, say, Photoshop. Next, we have to add these maps to the material in such a way that they will change from one to the next depending on the amount of light received. This is achieved by using multiple Falloff maps in the diffuse slot, with each pencil texture applied in the dark slot (from darkest to lightest), and the next Falloff map in the light slot. And so on until all textures are used.

Ensure that each pencil texture set to screen environment mapping, so it appears that the image has been applied directly to the ‘paper’ and not wrapped around objects. The beauty of this method allows you to even use raytracing in your materials, and by copying the falloff map tree into the Basic Tinting slot of the Raytrace map, you can even make reflections appear in the same style, or not, depending on your preference!

You could also make the hand drawn effect more effective by using animated pencil textures, about 10 frames should do for each pencil shade, to give the impression that the entire animated sequence does not move behind the sketch effect.

	The original scene consisting of basic Max objects, lit simply with Omni lights and no materials applied.
	The same scene with only the ‘Pencil NPR’ and ‘Pencil Raytraced NPR’ materials assigned. Note how the reflections in the teapots are also pencil shaded.
	Zip file to accompany - 3ds max scene & maps.

Initially published: 3D World magazine, Issue 15, August 2001.

Copyright © Pete Draper, August 2001. Reproduction without permission prohibited.

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