Archaeological Computing Systems Final

8/6/2019 Archaeological Computing Systems Final

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ARCHAEOLOGICAL COMPUTING SYSTEMS: AN INVESTIGATION INTO THEPOTENTIAL OF THE MENTAL RAY ENGINE TO ARTIFICIALLY REPRESENT LIGHT IN

THE NEOLITHIC SITE OF ATALHYK.

1. Introduction: Realistic Graphics in Archaeology?

Currently, many virtualreconstructions are limited because their level of realism cannot

be validated. The generated images may look realistic, but their accuracy is not

guaranteed since they have no physical basis in reality. (Devlin et al 2001)

There is great potential, but also incredible danger in incorporating three dimensional

technologies into the study of archaeological sites. In particular this is most poignant in

areas where reconstructions factor as both a base for visualisation and as an analysis

for artefacts and structures that are no longer present. Constructing imagery using the

latest programs and techniques can be an incredibly powerful, persuasive tactic.

Therefore responsibility lies with the artist to make sure any modelling is deemed to be

as physically accurate in all areas of investigation as possible, In order for the

archaeologists to benefit from computer-generated models and use them in a predictive

manner, they must accurately simulate all the physical evidence from the site being

reconstructed [Devlin et al. 2001].

One of the most important areas of research in this respect is lighting.

Rembrandt said that All is light, and within the commercial world of three

dimensional graphics, film, television and photography, it is perhaps the most vital tool

in conveying an emotional and physical response from the viewer. This is no different in

archaeological representation, without light there would be no scene and without

accurate shadows and illumination, the way the viewers respond to what they see can

be fundamentally affected, if we are to avoid misleading impressions of a site, then the

computer generated images should not only look real, but must simulate accurately all

the physical evidence for the site being modelled (Chalmers and Debattista 2005: 2).

This dependence upon light is echoed by Chalmers and Stoddart (1996: 87), who state


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that, In all image synthesis techniques, the fundamental step is computing the amount

and nature of the light from the three-dimensional environment that reaches the eye

from any given direction.

Lighting was also essentially for past societies, with a clear physical example

visible in the Orkney Islands, where the site of Maeshowe is orientated to face the

south-west, allowing light to spill into the monument only at the heart of winter. It

relegates the rest of the year within to darkness beginning, at the very point of

midwinter solstice (Richards 1996: 202) and it has been suggested that it signals the

death of the old year and the rebirth of a new year through illumination. Richards

(1996) clarifies that at its construction, Maeshowe would have represented the

landscape, fulfilling a role as a cultural and cosmological marker to its society.

Consequently, light defines more than what people saw, it lies at the very heart of

existence, influencing architecture and belief in a myriad of different ways, Light in

architecture is a complex phenomenon which penetrates every day practices and

rituals (Papadopoulos, C. & Sakellarakis, Y. 2010: 417).

In virtual imagery, this can be seen in the work of Gruber and Dobbins (2010),

who used a Maya script to generate virtual daylight in a model of the House of the

drinking contest in Antioch. Speaking about their model, they note that the software

was vital in analysing light at the site and that the ability to apply realistic, physical

lighting based on global positioning would have many uses outside of their project

(Gruber & Dobbins 2010: 422). Critically, their success in re-contextualising a series of

mosaics using the technology allowed them to be viewed in a way they cannot be

traditionally. Importantly, they felt their inferences using the software were reliable.

This desire for perspective is mirrored at the site of atalhyk. It is a place

where vision, expression and cosmology formed a valuable aspect of a society. If the

material culture remaining could be replaced into its original context these remains

could provide a great deal of information about life at a site, of unique international

significance (www.catalhoyuk.com).


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2.Aims: virtual accuracy at atalhyk

This project will attempt to discuss just how reliable the Mental Ray rendering engine is

in producing an image that cannot just be trusted visually, but also reinforced physically

in its ability to generate light. Speaking about Mental Ray in 2007, Joep van der Steen

comments that it is not only an engine with enormous potential, but possibly the best

available at providing beautiful, trustworthy imagery. Consequently, whilst it may not

be as efficient as other commercial rendering engines such as VRay and Brazil, this

ability to provide realistic equations is why it is placed at the heart of this study. The

features it contains extend to providing accurate techniques for Global illumination,

Reflection/refraction, Ray-tracing, Area lights, Bounced Light and Direct Light.

Following preliminary contact regarding reconstruction work at the site of

atalhyk in Turkey, a desire for a stringent test of Mental Ray was needed to convince

site director Ian Hodder into its potential as an analytical tool. The site holds many

conserved wall paintings, sculptures and other artefacts that are to be, enhanced by

virtual reality techniques and interactive video (www.catalhoyuk.com) and ultimatelyanalysed in their original context using three-dimensional software. A reference image

was provided of the onsite Neolithic House (Fig. 1) and from this a photorealistic,

physically accurate render was expected with lighting placed as the focus using a single

daylight system to light the entire scene. Future virtual study could be critical if such a

system can be relied upon to generate light accurately and from any global position.

More importantly, proving the programs ability and precision is crucial in providing any

rendered work from atalhyk with credibility, if computer reconstructions are to gobeyond mere digital images and models, and become a predictive tool for

archaeologists, physically-based rendering techniques have to be used. (Gutierrez et al

2008: 2).

This study will evaluate the stages taken to show exactly how much realism can

be attributed to Mental Ray, evaluating the positive and negative aspects of Mental Rays

light distribution.


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(Fig. 1) Reference Image from atalhyk, Turkey

3. Setting up a lighting Rig

There are various ways that 3DS Max and Mental Ray can light a scene, from the basic

three point lighting system (http://www.mediacollege.com/lighting/three-point/), to

complex scenes with multiple levels of lights, both standard and photometric

(Physically accurate). However, where considerable study is compiled into structures

such as those at atalhyk, dependent upon seasonal natural light, one of the most

important is the daylight system fashioned by the Mental Ray Sun and Sky package. To

use it within Mental Ray, all that is needed is to access the systems tab and create (Fig.

2). Once set, the Daylight system acts as a directional light source that exhibits crisp

shadows using the mrSun, to produce direct illumination, whilst the mrSky factors in

the many softer, diffuse shadows that provide the environmental bouncing of light. This

is formulated through the Final Gathering process that will be discussed later (Reinhart,

C, Breton, P.F, Landry, Marion 2008: 4).


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(Fig. 2) Setting up a Daylight System

As opposed to the IES equivalent, the Mental Ray Sun and Sky is the most

physically accurate daylight generator and is therefore focused upon in this project. Van

der Steen (2007) justifies this by saying it holds superior options, due to its ability to

provide soft shadows, haze and allow for changing cycles, I advise you to use this

mental ray Daylight system whenever you need to create an outdoor scene; it is far

better than the alternatives previously available inside 3ds Max. (Van der Steen 2007)

and importantly, it includes ways of accurately providing light from any location in the

world.

4.Analysing Light in Mental Ray

4.1. Direct Light

There are different aspects to compiling a successful lighting model using the daylight

system in Mental Ray, the first of these is direct lighting. Direct light represents the

exposed area of surface that is illuminated directly by a lighting source, in this case is

the Mental Ray Sun, Direct light is a pretty common term in the computer graphics

environment. Basically, it is light that is present in the scene in which all the light rays


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stop when they hit a surfacethere is no bouncing of light occurring. (Van der Steen

2007: 8). By highlighting the first areas of light, it provides useful visual information

about exactly where rays are falling and hitting surfaces. As shown below (Fig. 3), light

can be seen spilling into the room from its roof entrance, creating distinctive areas of

illumination comparable to those seen in the reference image.

(Fig. 3) - An Example of direct light using only the mrSun

To determine what the viewer should see, Mental Ray shoots light into the scene

until it comes into contact with an object. It is then passed through a shader that

describes how the material should look, before colouring the pixels for the resulting

image. (Van der Steen 2007:7). As shown in image (Fig. 3), when isolated, the Mental

Ray sun is very one dimensional, providing very intensive shadow and rays of light

without any soft shadow. This light simply represents the first stage of accurate

illumination as Mental Rays real power lies in indirect lighting.


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4.2. Environmental Light: Its Role.

The sun on its own cannot create accurate light, there needs to be another dimension. Inreal life, a huge aspect of lighting is comprised of indirect, environmental light. As light

radiates outwards, it hits various surfaces and fragments, being either absorbed or

reflected into the surrounding environment. How it bounces and how it returns from

the various surfaces it hits is down to numerous factors including translucency, density,

colour and texture. If a ray hits a smooth object it can be reflected in a corresponding

angle to the one that it arrived in, a mirror is a good example of this. This is called a

specular surface. In contrast, light can also hit rough surfaces and be scattered in aseries of different directions. These are called diffuse surfaces (Van der Steen 2007: 7).

Natural light is therefore comprised of both direct light (direct illumination) and

crucially, scattered, environmental light (indirect illumination). In Mental Ray an entire

element of the rendering engine is dedicated to this factor of lighting, highlighting its

importance. In any renders of atalhyk, bounced light will hold a crucial role

importance due to its ability to recolour surfaces, highlight different areas of shadow

and create pockets of illumination. Understanding this aspect of light is essential and

when applied to atalhyk could be used to understand structures and their uses. This

is shown by Papadopoulos and Sakellarakis (2010) in their assessment of natural and

flame lighting on the usage of a potential pottery workshop.

4.3 Shadows

With indirect illumination detailed shadow is created and in Mental Ray these areachieved primarily using ray tracing. This casts rays to every light in the scene from the

point that is being rendered, and checks if the rays intersect any of the objects on its

way. If so, the point is excluded so that a shadow is generated. Obviously, based on the

materials and how light bounces throughout the environment different coloured and

weighted shadows are created, Opaque objects create full shadows; transparent

objects create density and coloured shadows, based upon how much light travels

through the object material definition. (Van der Steen 2007:8). Without environmentallight, the human eye would instantly spot unnatural differences in perception, due to its


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constant experience of such phenomena in real life. A good isolated example of this can

be seen below (Fig. 4), where environment light from the scene has been alienated to

highlight how bouncing light moves through the room, creating gradient like shadows

and areas of light fallout. This is drastically different to (Fig. 3) that is very crisp, with

areas of drastic light and dark contrast. The balance between these two natural

phenomena is further emphasized in (Fig. 5), where both elements have been combined.

(Fig. 4) Isolated Environmental Light using the atalhyk Model

Fig. 5) Combination of Direct and Environment Light


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4.4 Mental Rays Indirect Illumination

There are two main ways Mental Ray can create environmental lighting, Final Gatherand Photon Mapping (Global Illumination). Both of these techniques generate bounced

light in different ways, presenting potentially different results and both can be used

independently of each other (Respective of the light setup) or be linked together.

Although both techniques may show differences, critically, they are both 100% correct

physically. These differences are usually due to the shaders used inside the scene and

not the underlying algorithms (Van de Steen 2007: 12).

4.5 Final Gather

Final gather is way of generating the indirect light that occurs in real life lighting by

firing light rays around a scene in a very similar way to how light bounces in reality,

with one fundamental difference, The rays used for Final Gather do not originate from

light sources or a camera; they originate from the geometry itself. (Van de Steen 2007:

12). This means that the Final Gather technique shoots rays into the environment and

then back to the light source to collect information and analyse shading. This

information is then compiled to decide how much light reaches the origins of the final

gather rays. It is then cross referenced with neighbouring points and averaged to create

smooth shading.

Within Final Gather there are a series of options that control the spread of

indirect illumination that are crucial to the rendering process. These are Rays, Point

Density, Interpolation and Bounces. To use an analogy, every final gather point

shoots an amount of rays back towards the light source like fingers from a hand and

logically, the more points that are shot, the more information that can be computed.

Point density controls how many points are within the scene and defining more FG

points will provide a greater spread, pushing the total amount of information that can

be collected up, and thus increasing the quality of the image. However, there is a drastic


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change on the render times and as visible in (Fig. 6) below, point density and the

amount of rays in a scene only really increase in the very highest settings of Mental Ray.

The interpolation works like a catchment area, looking for a certain amount of

points around the pixel in question and when it finds this amount of rays, it then

averages out the result and as before, the higher this setting, the greater accuracy in the

spread of toning across an image. A benefit to this setting in Final Gather is that it can be

increased without a real drastic difference in rendering times, as can be seen in the

graph below (Fig. 6). Taking in large interpolation settings will make sure that a blotchy

image (Fig. 10) is avoided, as small areas can result in pockets of drastically contrasting

pixels, making the image look uneven and noisy.

Bounced light affects how many diffuse reflections there are in the scene. It is

created when the Mental Ray Engine is told to refract light off of a surface, so that the

light carries on in the scene (Van der Steen 2007: 9)and as mentioned by Reinhart et al

in their study on the daylight system, bounced light is the single most important

attribute for accurate daylight simulation and, For interior renderings, a Final Gather

Bounce of 4 to 7 is recommended. (Reinhart, C, Breton, P.F, Landry, Marion 2008: 7).

There are drawbacks to using Final Gather. It can be too smooth, presenting

flickering in animation and it can also lack texture definition, but critically, it provides

accuracy in all levels of its use if used correctly.

FG Point Density Rays per FG Point Interpolate over Number of FG

Points

Draft 0.1 50 30

Low 0.4 150 30

Medium 0.8 250 30

High 1.5 500 30

Very High 4 10.000 100

(Fig. 6) Table showing the breakdown between the Final Gather settings


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(Fig. 7) - Point Density [0.1] Rays [1] Points [1]

Bounces [1]

This image shows a low spread of points with a low

amount of rays. Each point is firing a single ray that

is returning to the light of the scene. The

interpolation then decides how many points will be

used to find an average shade for the pixel. Using

very small settings can create a disco like effect.


Bounces [1]

The real difference in this image is the density.

Whilst the rays and bounces are the same, the size of

the clusters is much larger. Density is a great way to

increase detail in shadow, however it is one of the

problematic areas for drastically increasing

rendering times.


Bounces [1]

When Rays and Points are increased, the quality of

shading quickly progresses. This blotchy effect is

often seen in interior rendering as it requires a

greater level of atmospheric light than external

scenes. It simply represents the images above but

spread across a larger area.

(Fig. 10) - Point Density [1.0] Rays [250] Points

[250] Bounces [1]

With 250 Rays and Points, the image is finally

looking smooth and the catchment areas have finally

reached a happy medium where there are enough to

allow for consistent shading across the entire image.

To develop greater contrast in shadows, a high point

density is needed.


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The images below show the difference between one bounce and five. On first

viewing, the difference is unnoticeable, however increasing the bounces creates more

softened shadows, that gravitate towards the corners and crevasses of the room. Getting

shadows to form correctly is something that is incredibly important in demonstrating a

life like image to the viewer. It is very difficult to look between these images and find

instant differences, however where the real quality can be shown from the high bounce

image is in the subtle gradient of the shadows, the build up of shadow is a lot cleaner.

The images below represent a higher point density than is seen above (Fig. 10) and have

greater contrast.

(Fig. 11) - Point Density [4.0] Rays

[250] Points [250] Bounces [1]

The effect of the four bounces is very

difficult to distinguish between these

two images and is usually best seen

on shadows cast from objects,

however

When observing the different in the

tonality of shadow it is clear that the

image below provides a more natural

falloff.

(Fig. 12) - Point Density [4.0] Rays

[250] Points [250] Bounces [4]

Between 4-7 bounces produces a

model that realistically highlights

the amount of reflection that

happens in real life. When

comparing in particular the darker

areas of shadow, the smoothness

and realism in the quality of higher

bounces can be seen


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4.6 Photon Mapping

Globalillumination is a universal term for the description of a scene in which all aspects of light have been

considered as bounced, reflected, and refracted light. Rendering algorithms that calculate the way light

travels between surfaces of objects are called Global Illumination algorithms. The two most important Global

Illumination algorithms are raytracing and radiosity. Radiosity is used by the scanlinerenderer, whereas

mental ray uses ray-tracing.(Van der Steen 2007: 7)

Photon mapping is the second Indirect Illumination technique that is used by the Mental

Ray renderer. Unlike Final Gather, it works in a very similar way to how light is bouncedin real life. Using the mrSun (Or any Photon emitter), it fires small particles, called

photons towards the room, where these are either absorbed or reflected. Photons track

energy and colour wavelength, so this technique of indirect illumination is able to bleed

colour onto other surfaces, Photons in mental ray simulate the phenomena of real-

world photons. Photons are reflected by mirrors, refracted through glass, or scattered

by diffuse surfaces. The big advantage of photons is that they replicate what happens in

nature. (Van der Steen 2007: 12). The Global Illumination that is achieved throughusing photons is split into various sub-features in a similar way to Final Gather. The

most important of these include the amount of photons per sample (The look-up), the

sampling radius and crucially the amount of photons that are fired into the scene.

A larger amount of photons being emitted into the room will provide a greater

potential for information as there are more points to registering data from. These

photons are then collected within a radius that averages the amount of points set in the

max photons per sample setting. A 30 sample will there look for that amount within the

specified area size from itself and if there are more, it will retrieve the closest. Like with

Final Gather, if the radius is too small, or there are not enough photons to register a

consistent image, the results will appear blotchy (Fig. 13). It is therefore important that

all three of these key aspects are balanced so that the maximum amount of photons

entering the scene to fill it is combined with a decent sized sample to create a smooth

image in a radius that is not going to isolate areas of the image.


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(Fig. 13) - Photos per Sample [100] Radius

[0.5m] Average Photons Per Light [20000]

The blotchiness in the image to the left

highlights how a small sampling size can isolate

photons leaving uneven areas of averaged

shading

(Fig. 14) - Photos per Sample[100] Radius


Instantly, by increasing the radius in whichsamples are taken, smoothing can occur.

However, it is still only sampling 100 maximum

photons, meaning that the colour and energy

will still be very similar. To create a more

balanced image a larger sample size is needed.



Increasing the maximum sample size and

balancing it with the radius allows for more

data to be processed maintain a blended image.



We can finally see that 300 photons per sample

were needed to smooth the walls and the floor.

With this amount of data, Mental Ray can

generate a decent, smooth image.


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As with final gather, there is no direct science to which settings are needed, each

scene will require the lighting settings to be tweaked. However there are guidelines to

how to approach photons. As credited to Mental Images themselves, to achieve a

successful image by increasing photons, the user must, Shoot 4 times as many photons

in the scene from the light source, and then decrease the radius by a factor of 2. By

doing this, you will keep roughly the same amount of photons in the sample, but the

potential for a smoother image is increased due to more surface detail. Consequently,

van der Steen takes this further, stating that actually, We should have done the

following: divide the radius by 2, multiply the number of photons by 8, and multiply the

number on the lookup by 2; this is courtesy, again, of th e people from mental images.

(van der Steen 2007: 46).

When combining Photons with Final Gather, the first bounce is overlooked,

meaning that there is only need for one in the Final Gather settings. Photons will then

take over, and provide a rendered image that has, both great light depth in the shadows

and soft tonal variations in the lighted areas (van der Steen 2007: 12).

4.7 Ambient Occlusion

On top of the lighting mentioned above there are a number of other techniques that can

be used to further induce accurate light and provide depth to an image. One of the key

techniques for this is Ambient Occlusion. However, unlike Final Gather and Photon

lighting that is concerned with bounced light and multi-bounce transparency, Ambient

Occlusion is concerned at detailing the absence of light in order to develop a successful

shading method.

In the images below, the Ambient Occlusion shader has been used and whilst this

is not the only way to achieve such an outcome, it provides a nice balance to being able

to provide an added dimension to lighting that can be independently edited, The output

can be used to modulate other render passes to achieve proper compositing in

postproduction (Figure 1.20). (Van der Steen 2007: 14). The theory behind ambient

occlusion is that there is an ever present light source in the scene (Irrespective of our


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lighting system). The amount of shading is distinguished by how much of the geometry

is hidden, or blocked, What happens internally is that the area above the point to be

shaded is sampled for blocking geometry. If any is found, the percentage of blockage

translates directly to an occlusion factor. (Van der Steen 2007: 14). It therefore

calculates based on their visibility how much shading the pixels should get. To properly

achieve it using an occlusion pass (Fig. 18), exposure and final gather need to be turned

off and the entirety of the objects in the scene are overwritten by a specific, mental ray

shader. On top of simply being used for shading, Occlusion can also be used on a

specular level, to develop a higher level of detail regarding reflections visibility.

Whilst in the images below it is difficult to instantly see what impact ambient

occlusion has to the image, in the corners and where objects sit in front of each other, or

occlude view, the difference is remarkable. In terms of credibility, Ambient Occlusion is

a tool that can be used to simulate an extra dimension to provide an image with depth,

however its use, particularly in post production is an aspect that needs to be stringently

modelled based on an understanding of natural lighting, a knowledge rapidly developed

through consistent work in virtual lighting. This technique in particular is an area that

can easily be carried away with, potentially justifying Barcel (2000: 28) in hisdiscussions about archaeological accuracy falling behind the desire to demonstrate new

techniques. Ultimately it should be a very subtle effect, requiring definite responsibility,

but when used correctly, it can provide a great deal to an image.

(Fig. 17) - Ambient Occlusion Parameters.

The Ambient/Reflective Occlusion is placed in thesurface shader option of a Mental Ray material and

then into the Material Overwrite section of the

processing tab. On top of normal AO, the type can be

changed to create different results etc Specular

diffusion passes. The samples affect the smoothness of

the image, the trade off in higher samples is render

time. Spread tightens, or lossens the diffusion of the

occlusion similar to a Guassian Blur filter in photoshop.


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4.8 Participating Media

An aspect of internal lighting in particular that is often forgotten is how participating

media can affect the quality and natural equilibrium of an image. Especially within

archaeology, the need to represent different mediums that would have refracted light

through varying environments is important. With rooms like those found at atalhyk,

there are clear examples of hearths and fires that would have been used to heat and

cook in a fashion we have ultimately become out of touch with in contemporary society,

In archaeological sites in particular, the materials used to provide interior light, for

example, candles and wood fires, would have generated smoke, perhaps significantly

affecting visibility in these environments [Rushmeier 1995]. It is therefore important

to recreate these phenomena to provide accuracy in not just how the geometry looks

through light but also external, cultural and geographical factors like dust and smoke.

Within 3DS Max and Mental Ray there is a very realistic shader that can be

utilized to create these effects in a physically accurate form, Fog, clouds, and saltwater

scatter the light that passes through them; in other words, they contribute to the light

transport. To simulate this effect, you need a Parti Volume shader. ( Parti is an

abbreviation for participating.) (Van Der Steen 2007: 81). This spreading is caused by

tiny Particles and in Mental Ray this shader can produce a number of different effects

and must be applied to the camera shaders in the rendering tab of the rendering

settings. The main components for the shader are mode, scatter colour and minimum

and maximum step. Mode effectively changes whether the particles affect the entire

scene or simply elements of it. As its base setting, 0 will fill the entire scene and 1 willrelegate the phenomena to only certain areas before asking for a height modifier to

determine where in the scene it occurs. Scatter colour is incredibly important, as it

determines how bright the image is. As a default it is set to around 50% white, which

renders an incredibly over exposed image (Fig. 24). To allow for anything near realism,

this setting needs to be reduced to around 0.08% white. Minimum and Maximum step

effect the sample size and it is useful to start big (around 4.0/4.0) and then slowly

decrease until you get a smooth image(http://3dsmaxrendering.blogspot.com/2009/03/parti-volume-shader.html).


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The Parti Volume shader, like the Ambient Occlusion variant can be applied in

post production (Fig. 22) and I found that this was a very good way of using it. As can be

seen in the images below, when used with the original image, there was a fair amount of

issue with creating a clean output (Fig. 21). In comparison, by simply overwriting the

entire scene with a simple non reflecting black diffuse material, a very clean render pass

could be completed, highlighting not just the participating media itself, but also isolating

the phenomena and allowing a greater insight into its effect on the room.

(Fig. 21) - Natural Part Volume Pass (Fig. 22) - Separate Parti Volume Pass

(Fig. 23) Parti-Volume Settings (Fig. 24) - High scatter colour


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5. The Final Images(Fig. 25) (Original)

The photograph provided clearly

shows the areas of the image that

needed to be represented clearly.

Contrasted, dark shadows clung to

the walls and around the baskets at

the right wall, forming a very

distinctive pattern. Light entering the

room also left distinctive spread.

(Fig. 26) GI/FG (Image 1)

This is the image that combines both

final gather and global illumination.

It provides an accurate texture and

depth to the shadows. If there is one

criticism, it lies in the colour

bleeding into the room. It feels too

warm in relation to the photograph.

(Fig. 27) Final Gather (Image 2)

This image is much cooler in its

complexion and therefore closer to

the original in its colour. However,

only using Final Gather has made

the interior surfaces seem too

smooth. In comparison to the image

above, there is some depth missing

to the image, especially in regards to

lighting around the lip of the roof

entrance.


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(Fig. 28) -Analysis of light spill in the top-right corner. Left Original MiddleImage 1 Right Image 2

(Fig. 30)Top Original

Middle- Image 1 Bottom-

Image 2

(Fig. 29) Selection of the right hand wall. Left Original Middle - Image 1

Right - Image 2

It is clear from looking at the observations that Mental Ray has produced an

incredibly realistic series of images. (Fig. 29) shows how seamlessly the

three images are and in particular when comparing the Photon based image

with the original, as well as correct shadows, there is also a very similar

texture to the render. The Ambient Occlusion has also brought out theshading around the baskets and in the corners of the room successfully,

especially in image 1, where the light penetrates the area between the

baskets in exactly the same manner as the photograph, leaving accurate

arcs of shadow where they block the wall. If there is one criticism of the

Photon based render (Image 1) it is that the colour bleed is slightly off.

However that is a texture issue, not a light malfunction. The spilling of light

is identical in the renders, with the volumetric lighting provided the added

extra realism needed in representing the gentle haze (Fig. 30). The only real

difference between Image 1 & 2 is colour bleed and texture. If further workcould be completed to combine the mood of the Final Gather with the

texture of the Photons, the results could be stunningly accurate.


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(Fig. 31)Above - Colour Corrected Photon/Final Gather Render Below - Original Image

To produce something that can be regarded as physically accurate as possible in all regards, the levels on

the image were colour corrected to provide a more correct result. Whilst this was completed in post

production, any future work using the Mental Ray engine to render will provide firsthand experience of

textures as opposed to a second hand archive. This will enable greater accuracy in their creation and

colour. If there was a drawback to this project it was that the model was created without the author

having any measurements, or experience of the site.


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6. ConclusionA great deal was learnt by examining Mental Ray. In looking at the final output images, it

is clear that there is great potential in the rendering engine to deliver clean, reliable

imagery. When comparing the two final renders to the original, physically, the way the

light is falling is incredibly realistic. Furthermore, although each render has slight

differences, they both fulfil the claim by van der Steen (2007) that they are 100%

physically accurate (Figs. 26 & 27). This is remarkable considering the entire scenes

dependence upon a single light source. This trust can only be further extended with the

knowledge that the models geometry has been compiled from photographs and not

measurements.

This justification into the power of Mental Ray is incredibly important for work at

atalhyk where a synthesis of virtual reality could present art and culture in its

original habitat, providing a new dimension to both research and viewer experience.

However, this is not just important from an aesthetical and luminary view, accuracy

becomes even more important when taking into account how light affects both

perception of space and crucially such cultural inferences as art, religion and the

domestic household at atalhyk. It is hopeful that future work at the site will have as

successful an impact as the work in Antioch where contentment in their software

evolved to new understanding, it may invoke a new and more accurate level of

comprehension of ancient environments (Gruber & Dobbins 2010: 424)

To conclude, the author feels that Mental Ray has proved an immense amount in

this study. From its use of Final Gather to its Ambient Occlusion, the final images created

by the engine have shown a level of realism down to the smallest detail. Shadow and

light has been accurately represented and Mental Ray has been a resounding success in

laying the groundwork for exciting future work reconceptualising physical culture at

the site. In contemporary society it is easy to forget how involved light was in Neolithic

life, However, it was not the case in ancient times (Papadopoulos, C. & Sakellarakis, Y.

2010: 417) and it has not been the case on the part of the author.

Mental Ray offers a sublime ability to both balance photorealism with accuracyand at atalhyk with detailed observation and solid software, virtual reconstruction


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can provide new understanding about how art and culture influenced life in one of the

oldest cities in the world (www.catalhoyuk.com).
http://www.catalhoyuk.com/http://www.catalhoyuk.com/http://www.catalhoyuk.com/


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References

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Bender, B. 1998Stonehenge: Making SpaceOxford: Berg

Chalmers, Alan , Stoddart, Simon. 1996 Photo-Realistic Graphics for visualising

archaeological site reconstructions in, Imagining the Past: Electronic Imaging and

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Diego Gutierrez, Veronica Sundstedt, Fermin Gomez, Alan Chalmers, Modeling LightScattering for Cultural Heritage.ACM Journal on Computing and Cultural

Heritage, 1(2). ISSN 1556-4673, pp. 115. October 2008

Gruber, E. , Dobbings, J. 2010 Illuminating Historical Architecture: The House of the

Drinking Contest at Antioch in, Fusion of Cultures, Abstrats of the XXXVIII Conference

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Melero, Pedro Cano & Jorge Revelles, Pgs 421-424


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Kantner, J 2000 Realism vs. Reality: Creating Virtual Reconstructions of Prehistoric

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Van der Steen 2007 Rendering with Mental Ray

www.catalhoyuk.com (Accessed 22/05/2010)

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thomas.net/pages/free_tutorials/tut_ambient_occlusion_shader/ct_tut_mentalray_ambi

entocclusion_shader.htm- (Accessed 20/05/2010)
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Documents

Archaeological Computing Systems Final