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FULLDOME 3D FOR EVERYONE全景球幕立体解决方案!  

2013-11-09 15:10:24|  分类: 图像技术 |  标签: |举报 |字号 订阅

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written by Roberto Ziche
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THE RESEARCH AND DEVELOPMENT

The Stereo Domemaster shader is the result of an innocent question asked by a friend at the Chabot Space and Science Center in the Oakland hills, California, where I had been volunteering for just a few months.

Was it possible to create 3D movies for a dome?

I immediately thought that it would be possible, despite seeing immediately some obvious limitations. But it seemed like a good challenge to take on, and come up with a workable solution.

Fulldome 3D for EverybodyThe first round of research about existing technology, and 3D images in general, found that some proprietary technology existed, but adoption was very limited. Costs to enable 3D projection on planetariums were high, but in my opinion, it was the classic chicken and egg issue. As long as production of 3D content was limited because of scarce tools availability, 3D on domes would have never been mainstream.

So, a free, open source solution, seemed like a good idea for a start. The chosen missing production tool was a lens shader for one of the most common 3D content creation tool: 3ds Max and mental ray.

A lens shader is a plug in for mental ray that modifies the way a camera sees the scene. The way I wanted to use it was to overcome the limitations of the common 2-cameras rigs that are used in the production of traditional “flat screen” 3D movies.

Armed with my high school level math and geometry knowledge, and after 15 years that I didn’t write a single line of C++ code, I enjoyed every single minute of those 6-7 months of research and development I squeezed out of my spare time.

THE DOME LIMITATIONS

3D on a flat surface, like your TV or movie theater screen, is the easiest form of 3D. I didn’t say “easy”, as it still requires lots of understanding and tweaking at the capture (or rendering) and post-processing stages, but it’s a limited view area with predictable viewing positions that can be easily understood and addressed.

Fulldome 3D For Everybody - Dome Limitations

Left: Left and right cameras take images of a subject.
Right: The same images projected and filtered for each eye reproduce the 3D effect.
Both setups are horizontal, simplifying the whole process.

The dome is a different beast.

Imagine a horizontal dome, and for the sake of simplicity, just ignore the upper part, and focus on the lower edge. It might help to think of a cylindrical screen, open at the top.

It’s easy to see that a standard fixed 2-cameras/2-projectors setup wouldn’t work. If we simply extend a traditional screen and wrap it around the viewer, we would create areas where the 3D effect would be null as the cameras appears aligned.

Fulldome 3D For Everybody - Fixed Cameras & 3D effects

Two fixed cameras with a wide field view lose the 3D effects on the sides a the points of view align.

Even worse, in the area on the back side (not shown in the illustration above) the effect would be reversed, as the cameras effectively swap their position.

What’s the problem here? The problem is that the rendering process can create the wrap-around image in one go (through a 360 degrees lens shader), and this is a common technique in 3D renderings, but in reality, a human looking around a panorama, will turn his head. A fundamental difference for 3D effects to work.

If we could put a lot of traditional 3D screens side by side, wrapping around the viewer, the effect would be maintained, as now the cameras/projectors pairs rotates as the viewer’s head does, but would require multiple renderings, one for each screen, or “slice”.

By reducing the width of each screen, and increasing the number of slices, edge distortions and misalignments would be minimized, and with an infinite slicing of the cylinder, we could create the perfect viewing experience.

Slicing is a common method used for real life 3D capture of panoramic or dome images, and the number of slices needs to be something manageable. But since here we are talking about computer generated images, reaching infinite slices is perfectly possible.

THE VIRTUAL POINT OF VIEWS TECHNIQUE

The solution is pretty easy, and it’s not something new. For cylindrical screens Paul Bourke already proposed a solution. His web page is full of excellent research papers and documentation for domes and stereoscopic imagery.

My inability to read complex papers and the different goal of my shader made me set existing papers aside and come up with my own set of formulas. My findings are probably close to the ones described in Paul’s papers, but added some extra control parameters that I would need to control the 3D effect on different areas.

The lens shader is applied to a camera in the 3D world, and starting from the camera orientation, creates two point of views (left and right eye) that constantly rotate to look directly at the point of the dome where the pixel being rendered will be projected.

Fulldome 3D For Everybody - Interactive Simulator

In the illustration above, the virtual points are visualized as red (Right eye) and green (Left eye) markers. This screenshot is the interactive simulator I built to develop the actual formulas for the lens shader, and allowed me to visually see the effects of all parameters.

THE CONTROL PARAMETERS

As we move from the cylindrical screen to a dome, we need to take into consideration a lot of other issues.

For example, a dome could have concentric seating, or all seats facing the same direction, Also, domes could be horizontal, tilted, or vertical.

Fulldome 3D For Everybody - Tilted domes

Stereo images generated for a tilted dome need to take the tilt angle into consideration to correct the convergence to the side of the dome. While the turned head remains horizontal (red lines) the Left and Right images on an uncorrected domemaster image pair would converge following the dome tilt (blue arrows).

Viewers in a dome facing the same direction will look at the top of the dome with their head facing forward, but look at the back by turning it 180 degrees.

Fulldome 3D For Everybody - Front & Back

A) The easy area, where everyone looks forward, like in a standard 3D movie.

B) The sides, where dome tilt need to be taken into account to achieve proper convergence.

C) The top area, where users will still look with their head facing forward while the default lens shader would instead try to turn the virtual cameras.

D) The back area where users need to turn their head around.

The top of the dome also pose a challenge because the virtual cameras rotates (remember the cylindrical screen example) and in the small area at the top would generate a pinch effect.

Fulldome 3D For Everybody - Pinch effect

The pinch effect at the top of the dome for the right eye. The distortion on the reference grid is clear. The left eye pinch would be clockwise instead. The 3D effect in this area would be impossible for a person to see.

To solve those problem, and to allow the generation of images for all sort of domes orientations and seating layout, I added a series of maps that can control individual 3D effect parameters for each point of the dome.

The controls are three:

  1. The cameras separation multiplier allow the cameras to be moved closer up to be coincident to eliminate the 3D effect.
  2. The head turn multiplier allow to match the direction of the viewer head and force it to look forward.
  3. The head tilt allows for side tilting of the head to align the eyes convergence with the most natural head orientation viewers could assume for different areas of the dome.

The head turn multiplier can be used to control the top area of the dome and eliminate the pinch by forcing the head (or cameras, same thing in this contest) to assume a specific direction.

But by forcing the head forward at the dome top, and assuming that the viewer turns his head 180 degrees to look at the back of the dome, we create an area between the top and the back where the eyes position needs to be swapped.

That would create obvious artifacts, but if we eliminate the 3D effect in that area, the transition can be achieved without anyone really noticing.

Fulldome 3D For Everybody - Control Maps

Example of control maps (with dome reference overlay).
The Turn map forces the head to look forward in the front and top areas of the dome.
The Separation map eliminates the 3D effect in the area between the top and the back to allow the camera position switch.
The Tilt map can add a side head tilt in specific case. A 50% gray means no tilt. This map is rarely used.

Fulldome 3D For Everybody - Reference Grid

Example of a reference grid rendered using the Turn and Separation maps above. The front of the dome is the lower part of the image. Note the absence of any pinch and the transition area between the top and back of the dome.
This image if for illustration purposes only, and more refined control maps can be created.

The control maps can also be used to address any other dome style. On a dome with concentric chairs, you can use them to simply eliminate the pinch at the top. On tilted dome, 30 degrees or more, maybe with reclined seats, you can keep the head looking forward even for the back of the dome.

Fulldome 3D for Everybody - Solution for All Dome Types

A simple Separation gradient map can disable the 3D effect for all but the front part of the dome, providing an easy solution to create shows for all dome types.

 


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TILTED DOMES

The shader has a dome tilt parameter and a switch to enable automatic compensations. What happens when compensation is turned on, is that all the calculations are shifted and assume that the head of the viewer sits vertically, while the dome tilts.

This compensation is pretty effective, but remember that the tilt value might not be the actual tilt of the dome, but a combination between the dome, the reclined seat, and the headrest.

Fulldome 3D For Everyone - 45° Tilted Domes

An example of a reference grid rendering with a tilt of 45 degrees. Note that the pinch has now moved toward the back of the domemaster image. Control maps need to be adjusted for the proper dome tilt correction.

VERTICAL MODE

There is also a vertical mode switch. When that is selected, some parameters are ignored, and instead all the formulas change to automatically adjust for vertical domes, where the head stays vertical and the pinch areas at the top and bottom need a different type of correction.

Fulldome 3D For Everybody - Vertical Mode

Vertical mode simplifies everything. No control maps are really necessary, but they can still be used for example to control the left and right edge different image crop. Make this image small enough so that the centers separation is less than the distance between your eyes, and look far away. If you can focus, you will see a perfectly 3D room.

THE CAMERAS

The shader can generate images for one camera at a time. Your animation will have to be rendered twice, first for one eye, than for the other.

There is an option to use the Center camera. That means that no virtual point of views are created and the shader behaves like a traditional Angular Fisheye.

Fulldome 3D For Everybody - Angular Fisheye by Daniel Ott

All the parameters of the lens shader as seen in 3ds Max.

The shader code is an evolution of Daniel OttAngular Fisheye code, and the Center camera option is meant to keep compatibility.

The Center camera code adds a few optimizations to the original angular fisheye code to make it a bit faster and more efficient.

THE TESTS

To test the shader I created a lot of still images and a few animations. I was able to test them simulating the domes on a dome simulator created in 3ds Max. The simulator was generating relaxed-eyed image pairs of what the viewer would see when looking at a specific area of the dome.

Fulldome 3D For Everybody - Images generated by Daniel Ott's Lens Shader

Above, are the Center, Left and Right domemaster images generated by the lens shader. As you can see, the top pinch has been corrected.

Fulldome 3D For Everybody - 3D Images

Above, are sample stereo pairs created by the dome simulator using the Left and Right domemaster images above. Relax your eyes and you will see them in 3D.

This simple simulator was able to verify that the technique and the math I developed were generating correct images also for tilted and vertical domes.

Real testing with animation was performed in a couple of opportunities. First on a 10 meters inflatable dome at Treasure Island, in the San Francisco bay. A big thank you to Timothy Childs for the opportunity and to let me see for the first time the result of weeks of work.

Later on, thanks to Aaron, I managed to get some time at the San Francisco Academy of Science planetarium. There I could check four test animations and verify that the dome tilt correction was working wonderfully. Another big thank you to Cheryl Vanderbilt, Kira Hammond, Michael Garza, Ryan Wyatt, Tim Horn, Tom Kennedy.

At that time Aaron Bradbury was already experimenting with the shader too. And since we used anaglyph glasses, he warned me that the red channel was quite dark.
In fact, two of my tests didn’t work well as the eye looking through the red filter could not see much.

But the two brighter tests were spectacular, with the 3D effect perfectly visible all over the dome, and with a surprisingly ability of the eyes to adapt when looking at the screen even with the head slightly tilted from the assumed position.

Open Source
The project is now open source and available on Google Code.





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ASTRONAUT 3D – A STEREOSCOPIC FULLDOME PRODUCTION

Astronaut 3D is our first foray into stereoscopic fulldome at NSC Creative. The original Astronaut was released in 2006 and since then has been screened at over 100 domes worldwide. It’s a film that is very close to our hearts and we felt that it would be the perfect place to begin our adventures into the world of stereoscopic fulldome.

PARALLEL VS PANORAMIC

Before deciding to go ahead with the production, we needed to figure out a good workflow and what tools we could use to get the best possible results. There are a number of solutions available but there are really only two methods of stereoscopic fulldome production; the parallel method and the panoramic method.

The parallel method is currently the most widely used for fulldome. The stereoscopic effect is restricted to the front and top of the dome; the effect flattens off towards the sides of the dome and is inverted when turned to look at the rear of the dome. Using parallel cameras also produces a completely negative parallax, that is to say, everything comes from the screen into the viewer space. It is possible to achieve positive parallax by converging the images in as a post-process or using toe-in cameras, but this can cause vertical disparities towards the sides, which in turn can cause eye strain from prolonged viewing. It is possible to use any 3D software and any rendering engine with a fisheye lens to produce stereoscopic fulldome using this method. It is a valid method of producing stereoscopic fulldome for specific types of shots but can be very restrictive for many of the more panoramically immersive shots.

The panoramic method, which is achieved using the Domemaster Lens Shader, allows for a high degree of control of the stereoscopic effect across the whole dome. It allows for positive parallax and also flattening areas of the image. It is designed for use with Mental Ray, so third party effects that use other render engines cannot be used with this method.

Astronaut 3D is rendered using the Domemaster Stereo Shader. As our workflow has been deeply rooted in finalRender for 10 years, a complete switch of render engine had a huge impact on the project. It added several weeks of additional R&D to find suitable alternatives for third party plugins and many more weeks converting materials and lights. Never-the-less, our decision to go with the Domemaster Stereo Shader was based on the fact that we could achieve an all-round richer stereoscopic experience.

ANAGLYPH TESTING

Anaglyph testing in a variety of colour coded glasses can be troublesome at best. The red lens in a typical pair of red and cyan glasses is dark enough to completely block the red channel of a typically low luminance projection system. Only a very bright system is really suitable for testing using this method. Due to the lack of any stereoscopic domes in the UK, this was our only means of testing during the early phase of the project. A good technique to overcome this issue is to apply a self illuminating, light grey checker material to all of the objects in the scene. This helps with colour and luminance issues and also creates surface texture with which the eyes can converge to build the 3D image. Another useful technique is to boost the red channel of the anaglyph image for dome viewing, but this can only be used moderately before it becomes detrimental to the 3D effect. We were able to do some anaglyph testing here in the UK on one of the very bright demo and R&D dome systems at theHoloVis campus and our thanks to them for the invaluable support.

Fulldome 3D For Everybody - Low Luminance Domes

Left: Light grey checker material for improving low luminance dome anaglyph reviews.
Centre: Standard Anaglyph is difficult to see in low luminance domes.
Right: Red Boosted Anaglyph for improving low luminance dome anaglyph reviews.

INFITEC TESTING

The Infitec system is the most widely used 3D system in stereoscopic domes, so testing using this system is essential to experience the film as most audiences will. A common issue I’ve experienced with several different Infitec systems is what I would describe as ‘glossiness’ of highly saturated orange and cyan. There is often a slight hue difference between each eye, which cannot be compensated for. Although it’s far from desirable to affect the colours in a film based on the viewing technology it may be worth reducing the saturation of the very highest saturated cyans and oranges to avoid these issues. I was able to do some Astronaut 3D tests on the infitec system at Fraunhofer FIRST in Berlin, which highlighted some additional issues regarding the opacity of the glasses. Thanks to Ivo Haulsen and Kay-Ingo Ahlers at Fraunhofer FIRST for accommodating this and also to Robin Sip for taking part in the review process.

SCRIPTED TOOLS

Fulldome 3D For Everybody - Toolset UI as seen in 3ds Max

Toolset UI as seen in 3ds Max.

I worked closely with our max scripter Philip Day to produce a set of tools to help speed up the feedback process. Using these tools we can make changes to the shader settings and render a stereoscopic image to view in anaglyph on the monitor. Stereoscopic fulldome images can be particularly hard to view on a flat screen, but with some experience it is possible to work in this way.

DIFFERENT DOME CONFIGURATIONS

It is possible to optimise the settings in the Domemaster Stereo Shader to work with many different dome configurations. Dome tilt and seating tilts are different in most domes, but the important factor to take into consideration is how people move their head in the dome. We spent a lot of time understanding how people move their heads during different types of shots and compositions, and this is what we worked with when editing values on the shader. To make sure we weren’t missing any issues that might arise from unexpected factors in other domes, we sent tests to several 3D domes around the world to get feedback from as many different systems and setups as possible. Many thanks to Shawn Laatsch at Imiloa, Annette Sotheran-Barnett from Sky-Skan, Miroslav Andel from Norrk?ping Visualisation Centre, and once again Ivo Haulsen for all the valuable feedback.

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DOMOGRAPHY

Fulldome by its nature allows many different viewpoints. It is important to understand how the viewer moves their head during each shot and to know what is achievable in 3D. If the shot is set up to allow exploration of the whole frame, the stereoscopic settings need to allow for this. If the composition is extremely focused, the settings can be optimised for the best results. It is also possible to animate between different setups during the same shot.

Judging the stereoscopy using still frames can be misleading. Head movements over a still image are very different to those during a moving shot. To get the best results, full shot reviews are a crucial part of the workflow.

It is perhaps most important to understand all of the stereoscopic issues related with eyestrain and headaches, commonly called ‘brain shear’, and how to avoid these in a multi perspective environment. There are many ways to accomplish this using the Domemaster Stereo Shader.

CREATIVE CONSIDERATIONS

Stereoscopic depth can be a powerful and creative tool. There are many creative considerations that should be made when working on the stereography for a fulldome shot. A wealth of information already exists about flat-screen stereography, but fulldome stereography has many differences to be explored. Different shots can have different motivations and emphasis. It is important to understand the aim of the shot before working on the 3D aspects.

AFTER EFFECTS STEREOSCOPIC SCRIPTS

A number of other useful tools work well alongside the Domemaster Stereo Shader and form a broader part of the stereoscopic fulldome pipeline.

For all post production on Astronaut 3D, we used After Effects. We also used a set of scripts written by Chris Keller to help maintain the stereoscopic workflow and preview in 3D.

Fulldome 3D For Everybody - After Effects Scripts

Top right: Stereoscopic toolset.
Top: Left comp preview and optimized anaglyph preview.
Bottom: Red and Blue layers representing Left and Right channels are synchronised using the scripts.

DOME VIEW

A virtual dome is a useful tool to use alongside the Domemaster Stereo shader for fast feedback of 3D. As our dome is open to the public during working hours, we use DomeView to check initial 3D renders before reviewing dailies in the dome itself. There is only so much testing you can do at this level in 3D as the projection size is another crucial factor when creating 3D. The positive parallax on the image below looks very small, yet when seen in a large dome this as perceived at an infinite distance away.

Fulldome 3D For Everybody - DomeView Interface

DomeView interface and virtual dome display.

AllSkyViewer is an excellent free alternative and there are several other virtual dome solutions available.

GRADING

When grading it is beneficial to know what sort of display system will be used and the typical luminance levels and colours it is capable of. Luminance issues can be compounded in stereoscopic domes due to the glasses and projector lenses. We added boosting to the lower end of the light levels in most shots to maintain balanced levels when viewing on a stereoscopic system. Also, to counteract cross-bounce in some scenes, we used a mask or vignette towards the rear of the dome.

As technology improves these grading techniques may no longer be relevant, but currently they should be considered during the process.

SHOT EXAMPLES

Fulldome 3D For Everybody - Fulldome shots

For the internal Space Station shot we used a high separation value and larger dome radius to emphasise the sensation of being in a cramped space. It is possible to see the heavy rear vignette, which helps with cross-bounce in this very bright and focused shot.

Fulldome 3D for Everybody - Fulldome Shots

The Neurons shot is very ambiguous and is usually looked at in many different directions as the viewer tries to understand the scene. The stereoscopic setup allows the viewer to explore the whole frame comfortably, whilst maintaining a rich contrast in depth through the complex structures.

Fulldome 3D For Everybody - Fulldome Shots

The centrifuge shot aims to disorient the viewer to highlight the topic being discussed. We wanted to emphasise this in 3D, by increasingly distorting the space throughout the shot. Due to the extreme camera movement the shot quickly became too disorientating in 3D, so we kept the stereoscopic effect very subtle throughout the shot.

Open Source Platform
One of the greatest things about the Domemaster Stereo Shader is that it is free and open source. This means that it is open to development by the fulldome community, so it can be improved and built upon. Most importantly to me though, is that it is freely available for artists to experiment with and push the boundaries of what’s possible in fulldome.

Further Information
Astronaut 3D was produced by NSC Creative at the National Space Centre in the UK. We’re currently working on our next stereoscopic fulldome film and continuing to explore the language of the medium.

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MAYA AND SOFTIMAGE FULLDOME STEREO SUPPORT

In photography one of the considerations a photographer makes when they shoot an image is the choice of lens. The lens will determine the focal length, the field of view, focus, and exposure of the final image.

Of all the lenses available to a photographer the most specialized lens is the fisheye lens. It creates a unique look that captures a whole environment in a single image.

Often when artists create renderings on the computer they overlook the creative possibilities offered by lens shaders. My interest in compiling the Domemaster3D stereoscopic fulldome shader was to provide artists with tools to simulate a variety of physically accurate fisheye lenses.

Fulldome 3D for Everybody - Domemaster3D Shaders

There are four shaders that make up the Domemaster3D fulldome shader collection.

The Maya and Softimage versions of the Domemaster3D fulldome lens shaders work with the integrated stereoscopic camera rigs found in each package. The domeAFL_FOV_Stereo lens shader is connected to the stereo cameras in your scene and is used to render angular fisheye images suitable for projection in a stereoscopic 3D fulldome theater.

The Domemaster3D shader is compatible with mental ray and has been compiled for Maya on Mac OS X, Windows, and Linux, and a Softimage edition of the shader is available for Windows and Linux. The Domemaster3D shader also supports network rendering with mental ray standalone.

RENDERING IN AUTODESK MAYA

The Domemaster3D lens shader is compatible with Maya’s native stereo camera rig system. With the stereo camera rig in Maya it is possible to interactively create stereoscopic fulldome renderings in the render view using the anaglyph, luminance anaglyph, parallel freeview, and crossed freeview stereoscopic display modes.

Fulldome 3D For Everybody - Stereoscopic Viewing Formats in Maya

Maya supports 6 different stereoscopic viewing formats in the render view when the mental ray IPR renderer is active.

Fulldome 3D for Everybody - Domemaster 3D Presets for Maya

The Domemaster3D shader for Maya has a custom shelf with presets that simplify fulldome production.

The latest version of the Domemaster3D shader for Maya now includes a set of Python functions that simplify common fulldome production tasks. Now with a single click a stereoscopic fulldome camera rig can be added to the current scene. The Domemaster3D shelf also has the “AutoMagic” tool that creates a test scene with a stereoscopic fulldome camera rig, a simulated fulldome reference grid, and a few test objects.

Fulldome 3D for Everyone - Domemaster 3D Fulldome Shader in Autodesk Maya

When the Domemaster3D fulldome shader is used in Autodesk Maya you can view an interactive 3D preview of the final scene. This feature saves artists from having to switch to another program to review their stereoscopic renderings.

RENDERING IN AUTODESK SOFTIMAGE

The Softimage version of the Domemaster3D shader is configured using the node based render tree. When it is time to render your stereoscopic fulldome scene the Softimage “Render Manager” is used to render the left and right camera views as separate render passes.

Fulldome 3D for Everybody - Domemaster3D for Autodesk Softimage

This is the Domemaster3D fulldome shader running in Autodesk Softimage.

The Domemaster3D fulldome lens shader is based upon Roberto Ziche’s Domemaster Stereo shader for 3DS Max. The Domemaster3D shader also includes modified copies of the domeAFL_FOV and domeAFL_WxH shaders by Daniel Ott.

The Domemaster3D fulldome shaders for Maya and Softimage are open source and are available for download from the Domemaster Stereo Shader Google Code page.

For the latest news on the Domemaster3D shaders you can read the fulldome section on my blog.

more ifo:http://316studio.blog.163.com/

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