PAGE 16

MORE CLOUDS

Below the altitude and depth settings are those for 2d and 3d clouds. To get the best effect when using 3d clouds, you need to use the settings sliders on the render control panel.

render settings Just below the render preview on the render control panel is a button marked settings. This gives access to several options. When using 3d cloud rendering, it is important to take the cloud shading slider right over to high. For the picture on the right below, I have also taken the atmosphere slider over to high. Even though I have left the atmosphere settings at their default values, they will still have their effect on the sky and clouds.

The three boxes under miscellaneous are checked by default. We could speed up testing the effects of sky by unchecking render landscape, but I prefer to see the effect of our sky with its landscape so I have left it checked. The gamma correction slider can be used to improve the quality of the render if the previews have been too washed out or too dark. Our test previews seem fine, so I am leaving that setting at default.

On the sunlight/background light control I have switched to multi-directional shadow lighting.

Using the maxiumum accuracy on cloud shading and atmosphere, and checking ultra on the antialiasing options will greatly lengthen the render time. This is something you would normally do on a final rendering, after doing all your previews, even the hi-res ones, at the default settings for the two sliders and with ultra unchecked. I am making the comparison renderings a little larger for these two images, so that you can see the difference in quality more easily.

2d clouds3d clouds
These are the two renderings, the 2d clouds on the left and the 3d clouds on the right. The differences are subtle, but there are more shades of colour in the 3d clouds, and therefore they have a more natural appearance. The best area to compare to see the difference in these two renderings is the cloud right in the centre of the sky.

Using multi-directional shadow lighting has also improved the foreground hill on the left of the picture, which is no longer so dark

The picture on the left took 7 minutes to render, the one the right 25 minutes. You can see from the time difference in these two very small images, that in a full sized image, that would translate into a rendering taking perhaps several hours.

For the rest of the examples in this section I am reverting to 2d clouds and the default settings for atmosphere and cloud shading accuracy on the render control settings page, though I shall leave the multi-directional shadow lighting in operation.

darker colourcloud darkeningBelow the 2 and 3d options is the button for changing the cloud colour. The default colour, a medium grey, gives very realistic colours under blue sky conditions. For the picture on the left, I reduced the three colour values to 70, still keeping the neutral grey, but now a much darker shade which gives clouds which look as though they are going to gather together into rain clouds. For a sunset picture you might wish to reduce the blue in the cloud colour, to give a more yellowish tinge to the clouds, or to increase the red a little.

In the picture on the right, I have used the slider at the bottom left of the cloudscape generator, to increase the darkening on the cloud lighting settings from its default 25% to 50%. This has darkened the clouds even further, and their being small and few, together with the bright blue sky and the sunlit landscape, is beginning to look inappropriate with the blackness of the clouds gathering. At the end of this section I will render a gloomy overcast sky, with an appropriately dull and shadowless landscape.

density shift 15density shift 40We can increase the number of clouds by moving the density shift slider at the bottom right of the cloudscape generator from its default position of 0 to 15. If you then click the update view button you can see the increase in the cloud coverage in the two display panels. The picture on the left is at density shift 15, and the one on the right at density shift 40. In the second one, there is little blue sky left, but the clouds themselves are rather too blue now, and even though I have reduced the blue content of the cloud colour now to 55, we should really, for a more realistic picture, now reduce the blue in atmospheric blue on the atmosphere controller. We have already changed the simple haze colour, because in the current version of Terragen simple haze is used for the cloud colour, and changing one changes the other.

density shift=-15density shift=-100Taking density shift to negative values will reduce the number of clouds in the sky. On the left is the render at density shift -15. At -100, seen on the right, we get a cloudless blue sky.

Density contrast changes the contrast between the light and dark areas of the clouds. At a lower density contrast than the default value of 50, (below left) there are few shades of colour and the clouds look softer. At a higher density contrast, (below centre) the difference between the darker parts of a cloud and its 'silver lining' is emphasized. Increasing the density contrast will also increase the percentage of clouds in the sky.

density contrast=10  density contrast=150   shift down, contrast up

These very contrasty clouds are particularly useful in scenes where the sun is in or near the picture and the glow factors are higher. If the colour contrast is required without an increase in cloud coverage, the density shift slider is taken to a minus figure to remove some. The example (above right) has density contrast at 150, density shift at -10.

The update view button applies changes in parameters to the existing cloud pattern. The generate clouds button allows a new pattern of clouds to be produced. There are two other controls available when this button is activated, and a third, recurrence, which is not implemented at the time of writing.

largest cloud maximum-1The largest cloud size control is self-explanatory. In the picture on the left I have taken this control to one place below its maximum setting, which has resulted in one very large cloud. However, it was a rather lifeless and colourless cloud, so for the preview you see here, I also increased depth/thickness to 20 and density contrast to 75 to give it some bulk and colour, and took density shift to -2 to prevent density contrast from increasing the overall cloud cover.

After setting all these controls you must click on generate clouds to get the new cloud pattern. In fact, I clicked on it 3 times to get a pattern I thought would be useful in this tutorial. The first two generated clouds which were either at the side of the image, or would have been hidden by mountains leaving large expanses of blue sky, and so would not have shown you what the largest cloud control was doing.

You can see that it is unusual to change just one of these controls. It soon becomes necessary to change others to improve on what the first one does, or even to constrain the operation of the first one.

large clouds plus persistencesmall clouds plus persistencePersistence governs the number of very small clouds generated around the ones governed by the largest cloud size figure. In the picture on the left, largest cloud size is at maximum -1 as before, but now persistence is at 80. Cloud depth/thickness is still at 20, but because persistence produces rather contrasty clouds, density shift and density contrast are returned to their default values. The result is that there are big clouds, but there are also many little tiny ones around them.

With largest cloud size at minimum +1, persistence at 80, density shift at -10 and depth/thickness at 8, a skyscape of tiny clouds is generated. (right)

gloomy dayThese are the settings I changed to generate the gloomy weather scene on the right.

Cloud generator
cloud darkening=40% depth/thickness=20 altitude=60 density contrast=50 density shift=10 persistence=25 largest cloud size=maximum -3 cloud colour=R,G,B all set at 76

Lighting conditions control
Direct sunlight/sunlight strength=50% background light/shadow lightness=64 and multi-directional shadow lighting

Atmosphere control
Atmospheric blue colour=R,125 G,125 B,256

On the final page I shall generate a skyscape and make a final rendering of the sunset, snow and water scene we have been building up throughout the tutorial, but before that we are going to look at the scripting feature which brings animations to Terragen.

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