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..::space clouds::..

The closer you view textures, either by zooming / panning towards or distorting them, the more the colours and patterns have a tendency to bleed together and become very blotchy. This is due to the program trying to blur out the texture's enlarged pixels that are being displayed which normally wouldn't be seen so closely. Turning supersample on would sometimes fix this problem (another way would be by blurring the texture further depending on the requirements), but if you're getting closer still to the texture then drastic action may be needed.

The problem with cloud maps is that if you look closely to some NASA reference material of the Earth taken from a low orbit, then you can in some places see the sides of the clouds and not just the top, which is what a wrap-around texture is obviously based on. Somehow we have to add detail to the texture depending on what angle the camera is at to the Earth's surface and where the Sun is positioned to add depth to the bumps.

Creating an overlaid bump texture in Photoshop is one method, with a nice turbulant cloud texture. This could be created from cloning parts of numerous cloud views to get a nice variation in texture. The resulting texture would preferably be larger to get a closer view (but still maintaining the same aspect ratio) and would be overlaid on top of the existing texture (maintaining the existing texture's opacity) in the 3D package's diffuse (if necessary), specular, opacity (if required), diffuse roughness, diffuse level and bump slots for the cloud's material. However a method of fading out the texture back to the original depending on the distance from the camera would be required (such as a Falloff - Distance Blend map) else when the camera was panned back, the overall cloud surface would look slightly odd.

This method works, provided, again, you don't get too close to the cloud texture else the image tends to get slightly blotchy. Also at extreme angles the sides of the clouds are not all that visible. Therefore another method needs to be determined. If your 3D package allows, mix procedural textures using a smoke map (for the large cloud puffs) with a noise shader in the darker of the two colour slots to add smaller clouds puffs so the result isn't so uniform. Using the existing cloud wrap-around texture as a mask for the procedural noise, instance-clone the full stack into the specular, bump, diffuse level and diffuse roughness slots (if applicable).

Using the original wrap-around texture this way won't be a problem, even zooming the camera in really close to the clouds as the blurred and blotchy edges of the texture will be replaced by the detailed procedural texture, which, as it's generated by the 3D package itself, won't become blurred or blotchy, but will remain crisp throughout. A couple of additional points though. Procedural textures as a whole have a tendency to take longer to render than textures due to the program having to calculate and create them itself. Also, if the camera is being zoomed right in (so it's just about to pass through the cloud layer) it might be worthwhile adding an additional noise map to the white colour of the smoke map just to add more detail at closeup. Again, as with the overlaid texture map example, falloff masks linked to the camera's distance (or do two sets of renders and fade between the two in post) should be considered for the procedural example also.

Enlarge ScreenshotThe normal render of the cloud's surface appears flat and blotchy due to the texture being viewed closer than normal.
Enlarge ScreenshotBy adding a mixture of procedural textures and using the wrap-around texture as a mask, added depth and detail can be added even at close views.

Initially published: 3D World magazine, Issue 5, November 2000.

Copyright Pete Draper, November 2000. Reproduction without permission prohibited.

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