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.
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.
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.
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).
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.
normal render of the cloud's surface appears flat and blotchy due to the texture
being viewed closer than normal.|
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.|
3D World magazine, Issue
5, November 2000.
Draper, November 2000. Reproduction without permission prohibited.