PAGE 6

ATMOSPHERICS

There are three settings on the Atmosphere control panel. Each has sliders for adjusting density or decay and half height, and a button which accesses the colour control box. These settings are often more effective if used in conjunction with the light settings - the sun direction, strength, glow power and so on, but it is also important to know the effect of changing them on their own. In these comparisons, I have used as the control picture the settings used for the last render, on page 5.

First, I want to look at the centre one of the three settings, atmospheric blue. This is the setting which controls the colour of the sky, the reflection of the sky in water, and so on. You can change the colour of this atmosphere, by clicking on the colour button, but simply changing the sliders can usually give all the control you need for a natural scene. I have taken the sliders to rather extreme levels to emphasize what they do. Normally quite small adjustments are enough to give the effect you want.

CONTROL
Density=20%
Half height=128
DENSITY UP
Density=75%
Half height=128
DENSITY DOWN
Density=10%
half height=128
HALF HEIGHT UP
Density=20%
Half Height=10016
control  density up density down half height up
You should be warned that raising the half height to levels like 10000 will greatly increase the render time.

The third setting on the atmosphere control is light decay /red. This is the control you will use most often when you are arranging sunset scenes. Again, although the colour of the light can be changed in this setting, but it is very easy to make the scene look over dramatic and unnatural if colour changes are too extreme.

For these tests, the atmospheric blue settings were restored to their defaults of 20% and 128, and the colour left at the default setting.

CONTROL
Decay=20%
Half height=128
DECAY UP
Decay=70%
Half height=128
DECAY DOWN
Decay=10%
half height=128
HALF HEIGHT DOWN
Decay=20%
Half Height=5
control, locked Decay up, locked Decay down, locked Half height down, locked
The effects of changing the colours on this one are different if the setting is unlocked from atmospheric blue. By unlocking the decay setting from the atmospheric blue setting you can balance the colours to give a convincing sunset sky, and changing the colour of this setting can also be useful in misty and moonlit scenes. If decay is locked to atmospheric blue, changes you make to atmospheric blue colours are mirrored in the balance of the decay colours. If you add red, for instance to atmospheric blue, a similar amount of red will be removed from light decay/red. If you have been changing the colours with the lock unchecked, as soon as you check it the colour of light decay/red will change to the inverse of the colour levels you used in atmospheric blue.

At the time of writing, the state of the lock to amospheric blue will not be changed if you reload a saved atmosphere. If you saved it, say, with the lock unchecked and have been working on another image with the lock checked, the check will not be reversed when you reload the first atmosphere and the colours in light decay/red will be reset to the inverse of atmospheric blue. If the colours in your saved image are not the same as you intended, reverse the check on the lock and reload the atmosphere.

I have left the simple haze setting till last because the changes in this setting are frequently best made in combination with other settings on this control panel and on the light one. I will do the same tests, however, so that you can see the haze setting in action. This is the setting which gives mist and fog, the basic colour to the clouds, depth to sunsets, midday heat haze, and so on.

Again, it is possible to change the colour of this setting, but I have only found a few occasions when it is appropriate to do so. The mist and the clouds take some colour from the sky and the other atmosphere settings anyway, and the scene is usually more convincing if this setting is left as a neutral grey and does not contribute conflicting colours to the scene. However, there are occasions when changing it can be useful. In misty scenes, for instance, the colour of the mist can be adjusted with this setting, to remove some of the residual blue which is difficult to eradicate with the other colours alone.

The variables on the other two settings have been returned to their default values.

CONTROL
Density=20%
Half height=128
SIMPLE HAZE UP
Density=75%
Half height=128
SIMPLE HAZE DOWN
Density=10%
Half height=128
HALF HEIGHT DOWN
Density=20%
half height =5
control simple haze up Simple haze down Half height down

On the next page we shall go on to look at combinations of settings to give sunset, moonlight, and misty scenes.

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