The Foundry showed some new features of the new MODO 901 release today in a webinar. While those features were interesting (see UDIM below), Mike Seymour has this exclusive look at some of the changes in the MODO renderer which the team did not discuss but are just as exciting.
The renderer in 901 is very much a viable production renderer. The MODO team could have walked away from making their renderer a serious production option, leaving the market open to third party renderers such as V-Ray, RenderMan, Maxwell or Arnold. After all, the primary strength of MODO is modeling, no one would be upset if their renderer was adequate for students and indie users but not really fast or highly optioned…well, everyone except the MODO guys, who are it seems committed to having serious render technology in-house. This core technology is not just for 901, but it is key to several projects still very much under wraps. It is also important given the cross-product module level technology swaps we are seeing, with key tech from all The Foundry products being swapped in each other’s product road maps.
In MODO 801, the renderer was very much in an acceptable category of speed and performance, but with 901 there have been some serious additions. Top of this list is Multiple Importance Sampling (MIS), an addition in the spirit of Eric Veach’s 1997 thesis (the bible that all the top renderers have consulted when implementing MIS).
In 1997 Veach, a Sci-Tech Oscar winner for his rendering contributions, published a range of key rendering theories which:
“…include a new technique called multiple importance sampling, which can greatly increase the robustness of Monte Carlo integration. It uses more than one sampling technique to evaluate an integral, and then combines these samples in a way that is probably close to optimal. This leads to estimators that have low variance for a broad class of integrands.”
In short, MIS produces much better results, more accurate and just as about as good as you can do. MIS in 901 has been implemented for diffuse and specular shading and is in complete sync with the move to area light sources. For both spec and diffuse, MIS can greatly reduce visible noise in MODO renders. In earlier releases, the shading was computed by choosing “random sample points on the light source, determining if they are visible by firing shadow rays, then multiplying the incoming light by the surface’s BRDF,” commented Shane Griffith, MODO’s Product Marketing Manager. “Or, if the user enabled the light’s Visible to Reflection Rays option, its specular shading was handled as part of computing blurry reflections, which involves choosing random directions according to the BRDF and seeing if rays fired in those directions hit the light source.”
From what we saw, both of these approaches are likely to be noisy compared to the same scene rendered with the new MIS approach for the same render effort. Users can activate the MIS using the Direct Light MIS channel of the render item. The user can specify whether to use MIS for diffuse shading, specular shading, both, or neither. As the renderer was not slow, comparatively speaking, this new solution will be welcomed by users for both its speed and improved noise performance.
In Veach’s 1997 thesis and in a paper he co-published just prior (1995 Veach & Guibas), this is an image which shows the problem and solution solved via MIS. In the original 1997 black and white original there are four area lights, varying in size by a factor of three from their neighbors (and varying in radiance by a factor of nine so that they each emit the same total energy).
(Note how in the Veach example, sampling the BSDF works for area lights and not tiny spots, and sampling favouring the lights does the opposite)
Below is The Foundry’s replication of this classic shot in three images each showing five rectangles using a highly specular GTR material with roughness settings of 2%, 4%, 8%, 16%, and 32%.
The first image uses traditional area light source sampling. This does not work well when the light is large and the roughness is low, because the chances are very small that a random sample on a large light source will fall within the very narrow specular lobe of a smooth, mirror-like BRDF. When such a rare event does happen, the result is an unnatural bright speck.
The second image shows what happens when the reverse is the case (again non-MIS) – the lights are specified to be visible to reflection rays, direct specular shading is turned off and blurry reflections are used instead. This does not work well when the light is small points and the roughness is high, as you can see below. This is because it’s unlikely that a random direction within the broad specular lobe of a rough BRDF will hit a tiny light source.
The MIS solution covers both cases, all three images are rendered in 901 and interestingly the render times are roughly the same for all three.
While the results are less dramatic for diffuse, MIS is used also for 901’s diffuse.
Adaptive Light Sample Allocation
“In 901,” explained Brad Peebler, The Foundry’s President of the Americas, “the ALSA (adaptive light sample allocation) direct illumination method adaptively allocates samples from a global count to the lights in a scene based on its estimated contribution. This can result in faster renders with less noise and requires significantly less user input. Faster, cleaner and easier to use. ALSA is a triple threat feature… Nice work from Mr. Hastings!” he joked referring to co-founder Allen Hastings.
ALSA is a new feature point – given the number of lights often required in a production shots. Massive numbers of lights slows the render, but with this new adaptive approach when there are multiple lights you can ignore the traditional sample counts for each light item, reducing render time dramatically. Instead, each light’s probability of being sampled will vary at every shading evaluation depending on factors such as the various light’s brightness and distance. The main benefit becomes apparent with large numbers of direct light sources. In such cases you can expect to see a very real reduction in render time and reduced noise.
In one test case a hall was lit by just 20 area lights and rendered in 801 and then again using the new MIS and ALSA in Modo 901. The traditional light sampling with four samples per light (for a total of 256 samples) and two bounces of Monte Carlo indirect illumination led to a render time of around 17mins. With the Adaptive Light Sample system this dropped to 6.5 mins or 300% faster and the image looked noticeably less noisy to our eye. As the number of lights increases fxguide saw test shots with even more dramatic results.
And below is the same file rendered in Modo 901 300% faster..
The test image used here was modeled by 3D artist Vaughn Ling, from Pasadena in the USA, – who Brad Pebbler remarked was “a great guy, talented artist and deserves some props!”
Other leaks from The Foundry included improved UV and UDIM tools – which will be very welcomed by many MODO users. While UV tools may not be sexy, the difficulty in wading through UV maps to get things to work is beyond annoying – it breaks the creative flow. While 901 has many other cool features which will be made public RSN (real soon now)…already the UV and MIS makes 901 a strong release.
More on 901 when The Foundry officially release the new version.
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