Info zum MH Subsurface Scattering Script

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Das Original [en] dieses Tutorials finden Sie hier.

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MH Tutorial: using the SubSurface Scattering script.

This tutorial aims at showing how works the SubSurface Scattering Script of the MakeHuman project [en]. The script is a different version of the Superficial Scattering script already featured on ::feeblemind.org::, and, as it can simulate the translucency of the material, it gives more realistic results for such materials needing transparency to be taken into account.

Hier können Sie das Script herunterladen: MHsss beta 04, and here you can see: The discussion about features and usage.

:: Preliminaries ::

Zuerst müssen Sie Lampen in Ihrer Szene definiert haben. Das Script wird diese einbeziehen (in welchem Layer diese auch gesetzt sind) und kalkuliert dann den Scattering-Effekt entsprechend ihrer Position zum Gegenstand, auf dem der Scattering. Effekt beabsichtigt ist.

Das Scattering wird als Vertex Color Light Information gesetzt. Dazu muß der VCol Light Button in dem Material-Tab innerhalb des Shading (F5 key) Menüs aktiviert werden.

Sie können natürlich das Script für alle Objekte innerhalb Ihrer Szene verwenden. Sie müssen dazu jeweils nur diese auswählen bevor Sie das Script auf diese anwenden.

• Setzen Sie mindestens eine Lampe
• Setzen Sie den VCol Light Button auf 'on', für das Material des Objektes
• Stellen Sie sicher das das jeweilige Objekt auch ausgewählt ist

Die Verwendung des Scriptes ist sehr einfach.
Teilen Sie Ihr 3D View in zwei Hälften. In einem davon, drücke Shift+F1 um das Script per Append zu laden. Wechseln Sie in das Verzeichnis in welchem Sie MHsssbeta04.zip entpackt haben und gehen zu MHsssbeta04.blend. Gehen Sie nun in das Text-Verzeichnis und wählen dort das MHsssbeta4.py aus. Wechseln Sie nun in einem der beiden Fenster in das Text Window (SHIFT+F11).
Klicken Sie nun den Auswahl-Button um zwischen den verfügbaren Textdateien auswählen zu können. Wählen Sie nun MHsssbeta4.py aus.
Starten Sie das Script anschließend mit Alt+p.
Die GUI des Scriptes sollte jetzt auf dem Bildschirm erscheinen.

• Epidermal scatter:
  The three sliders (Rt, Gt, Bt) set the tangential color of the scatter effect, e.g. the dermal color. They range from 0 to 255. The color should be as close as possible to the the base material color.
• Subdermal scatter:
  The three sliders (Rp, Gp, Bp) set the perpendicular color of the scatter effect, e.g. the subdermal color. They range from 0 to 255. For a human skin, the color should be red-like.

• Scattering:
  This rules the diffusion of the scatter effect through the object effected, by increasing or decreasing the luminosity and contrast of the scattering effect. Low value will simulate a very local scattering effect, while a high value will produce a scattering effect diffusing more widely through the object's surface. Starting with a low value (e.g. 0,15) is a good idea. It could range from 0.01 to 1.00.
  
  
  On this picture, only the Scatter value is changed (0.05 on the left, 0.15 on the middle, 0.35 on the right). The scatter effect grows in influence and intensity just as the Scatter value does.

• This sets the density of the material. The higher the density, the lower will get the scattering effect. The density is the same than the IOR for transparent objects. Here you can find an extensive list of material densities. For the script purposes, it could range from 0.01 to 4.00.
  
  
  On this picture, only the Density value is changed (0.5 on the left, 1.5 on the middle, 3.0 on the right). The scatter effect is really more important when low Density is encountered, as light can propagate more easily than when density is high.

• This rules the quality and the intensity of the scattering effect. A high value will produce a scatter effect of good quality and high intensity, but to the price of longer calculations times. It could range from 10 to 50 and starting with a medium or low value (e.g. 15 to 20) can be quite time saving for your first tests!

• Exit:
  This button simply exits from the GUI of the python script. All values and settings are automatically discarded.
• Save:
  This button lets you save the settings of the GUI. It's very convenient if you want to recall old values, or if you wan to run the script on multiple objects, each with their own settings.
• Load:
  This button lets you load settings previously saved.
• GO:
  This button starts the calculation of the scattering effect according to the settings of the GUI, on the object that is currently selected. It stores the result of its computations as VCol Light intensity.

• Maintaining the balance between the Scatter and the Density values:
  By increasing the Scatter value too much, you can get some strange colors artifacts. To get rid of them, you will have to maintain a good balance between the Scatter value and Density value. When both are strong, the artifacts are easy to spot. If you need high Scatter values, try to decrease the Density value. Obviously, in real world, it's frequently the case! Think of a paper lamp, lit from the inside by a bulb. The lamp will be mainly translucent due to the thin layer of the paper and its very light density: it has a high Scatter value and a low Density value.
• Dealing with density values:
  If you have no clue about the density of a material, use your common sense and start with the water value: 1.33. Then increase or decrease the value, according to the material buoyancy: if a small ball of the material floats on water, decrease the density, if it drowns, increase it. Keep in mind that human body's density is not constant, even if made out of 70% of water, so tweaking this value in order to get eyes-friendly results will be needed anyway for most organic objects
• Maintaining the lighting balance:
  As the script writes SSS results as VCol Light information, after using the script, it will be clearly visible even in unlit or dark scenes. If you have strong lamps in your scenes, and perhaps also make use of Ambient Occlusion, then your object could quickly become overlit. To correct this, you can make use of many tricks: decrease the Light Received value; decrease the Ref value of the Material shader; decrease the Iteration value.