Render Studio AO Tutorial

Render Studio for Poser: Ambient Occlusion Tutorial

Written by Karibou


Welcome to the first in a series of tutorials aimed at transforming your renders through the use of Render Studio for Poser! In a few, simple steps, this lesson should help you master the subtle art of Ambient Occlusion (AO) through the Advanced Ambient Occlusion Editor included in RSP. While this tutorial is aimed at novice artists, it contains some helpful tips that even veterans may find useful.


What is Ambient Occlusion?

If you closely examine a photograph which shows two objects sitting near each other, you can see that gentle shadows occur in the crevices and valleys that exist where the two objects touch. While many render engines are capable of producing fairly realistic and complex shadows through depth mapping and raytracing, the process which renders these shadows often falls short when it comes to creating those subtle details. "Ambient occlusion" is a supplemental shadow technique that creates the faint, natural darkening which occurs where two surfaces sit very close to one another.


When ambient occlusion is used boldly, the differences between an image without AO and one with AO are quite dramatic:



In the image with ambient occlusion it's easy to see the delicate shadowing around the eyes, under the necklace, and near the edges of the tank top. AO creates a sense of depth and realism that is lacking in the first image.


How Are Ambient Occlusion Effects Created?

With Poser 6 or 7 and the Firefly Render Engine, creating ambient occlusion effects is possible in two ways. The first method involves adding AO to one or more of the lights in your scene. However, since lights create AO effects uniformly over everything in their path, sometimes this method is not the best choice.


The second, more flexible method of adding ambient occlusion to your scene involves adding AO nodes to the materials which you want shadows to appear on. While it is possible to do this using just the Poser Material Room, adding many, individual nodes to a scene one-at-a-time can become a very time-consuming process.


This is where Render Studio for Poser becomes invaluable. With a few clicks, the Advanced Ambient Occlusion Editor (included with RSP) makes adding AO nodes to materials quick and amazingly easy.


How Does the Advanced Ambient Occlusion Editor Work?

You should start by posing and lighting your scene normally. When you are ready to render, you can add AO effects by running the "Advanced Ambient Occlusion Editor" python script.

In Poser 6, this can be accomplished in two ways. You can open the python window and then load the Render Studio menu to it. This brings up the following window, from which the AO Editor can be accessed:



You can also simply select the "Advanced AO Editor" option from your runtime's Figure menu, under the "!Render Studio" folder:



In Poser 7, it is even easier to access the AO editor. Simply use the Scripts pull-down menu and select the AO Editor from the RSP sub-menu:



When the editor opens, you are presented with a long list of all the materials in your scene, as well as several options for selecting the materials.



The first time you open the AO editor in your scene, you will probably see that none of the materials have AO nodes attached to them yet. Adding these nodes is very simple. Check the boxes next to the materials you want AO shadows to appear on, and then select "Add AO node" from the middle column of choices below the checklist. The Advanced AO Editor will then add AO nodes to every selected material in a matter of seconds.


Since there are often dozens of materials in a scene, the AO editor even makes it easy to select or deselect many materials at once. "All" and "None" are self-explanatory. "Select AO Materials" selects only those materials which have AO nodes attached. "Current Figure" selects all the materials of the current figure. "Invert" turns all open boxes into checkmarks and vice-versa. And "Choose" provides the user with infinite flexibility in selecting materials.


For example, in this scene, I have Victoria 4 (by DAZ3D) loaded into the scene. I know that V4's materials are grouped by number, with 1 being all facial materials, 2 being the torso, and 3 being the limbs. Typically, these are the materials I want AO nodes attached to, as they make up the external parts of Vicky's body. It is very easy for me to choose these materials using the AO Editor. When I select "Choose," the following pop-up window appears:



By choosing "1_" for face materials, "2_" for torso materials, and "3_" for limb materials, I can easily select all of Victoria's skin in one click.


When deciding which materials to include in your selection, you should first take a quick visual inventory of the scene. Don't select materials which aren't visible. Remember that you will see the most dramatic effects on surfaces which have crevices or valleys, or are in close proximity to other figures. In some very high-polygon figures, you may want to forego AO nodes, simply because it will overwhelm system resources during rendering.


Okay... But What Do All Those Settings Mean?!

After you have added AO nodes to your desired materials, you will see data about the nodes appear beside each AO material in the scene. When an AO material (or group of materials) is selected with a checkmark, there are three things you can change about their AO nodes: Samples, MaxDist, and RayBias.


MaxDist: I'll start by explaining Max Distance because it's the primary way to control how much AO shadowing appears in your scene. (Please note: the numbers shown in these screen-captures are displayed in INCHES. If you have Poser's default unit set to "feet," your numbers will look VERY different!) Maximum distance (MaxDist) is the approximate distance two surfaces need to be from one another for an AO shadow to be rendered. Objects farther than the maximum distance will not cast AO shadows. A large MaxDist will essentially cause more nearby objects to cast shadows on the material, thus creating a bolder AO effect. In the image shown below, you can see the difference between a render with no AO, and renders with a MaxDist of 4, 12, and 18 inches:



Note how the shadows around the eyes and under the necklace become much bolder as the MaxDist increases.


RayBias: This is also an important setting, but one which is primarily used to fix glitches in your render. Recall that the Max Distance is the farthest a ray of light can travel between two surfaces and still cause an AO shadow. In contrast, the ray bias is pretty much the opposite of this. RayBias is the smallest distance a ray can travel and still cause AO shadows. Ray bias becomes important when strange, blotchy shadows (called "artifacts") appear on your renders. Often, when artifacts are created, it's because the RayBias is too small. Increasing the ray bias by a small amount (perhaps increments of 0.1) will usually make these artifacts disappear. On skin, I typically use a ray bias of 0.4.


Samples: This number affects the numbers of rays sampled by the render engine. In nearly all renders, leaving the Samples setting at 3 is fine. In cases where you have a very large MaxDist, you may want to increase the samples to 4 or 5, in order to create a high-qualtity, smooth shadow. Be aware that doing so will increase rendering time.


Is There Anything Else I need to Do Before Rendering?


If you are rendering AO effects in Poser 6 or 7, you must use the Firefly render engine and have raytracing turned on. It's worth noting that when you use the Advanced AO editor to add AO nodes, the editor automatically changes your render settings to include raytracing.


If you are rendering in Poser 7, there is one other render setting you should be aware of, called "Irradiance Caching." Poser 7 uses Irradiance Caching (IC) to speed render times when Ambient Occlusion is present in a scene. When IC is set to a very low number, scenes render quickly, but AO shadows can appear splotchy or grainy. When IC is set to a very high number, scenes render slowly, but with higher quality AO effects. You can see the difference below:



Look closely at the shadows around the edge of the tank top. The image with the low IC has grainy, uneven shadows. Also, in the render with the high IC, you can see a clear, shadowed outline of the necklace just below the figure's collarbone which is not present at lower IC settings.


Other Tips and Tricks:

Unless you have a very good reason to do so, I recommend against adding AO nodes to hair. Because hair is usually quite complex, AO nodes on hair can bring rendering to a near-standstill. Artifacts are also common when AO nodes are applied to hair.


Another note about hair: if you are using depth-mapped shadows, you may want to turn raytracing completely off on hair figures. This will not only speed up render times, it will prevent the formation of artifacts along the hairline where the skullcaps of many hair objects contact a figure's head.

If you notice your figures appear to be hovering above the background or paper roll, even though they are touching it, you can add an AO node to the paper roll. With a high MaxDist, a very realistic shadow will appear on the ground. You can see the difference here:



Lastly, be careful about using the Advanced AO editor on textures which already have AO nodes on them. (When a product contains an AO texture, it is usually noted in promotional information or in the readme file, since not all versions of Poser support AO.) If you create AO nodes on a texture which already has AO nodes, be prepared for odd, artifact-filled results.


I hope that this tutorial has provided you a solid foundation for adding perfect ambient occlusion effects to your images!


Happy Rendering!


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