HDRI - High Dynamic Range Images
Please Note: This section was written many years ago, when D-SLR Cameras and HDRI techniques were in its infancy. I decided to keep this old page up as the basics remain the same, even though the technology has progressed in leaps and bounds since the early days.
All work on this site is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 2.5 License.
[HDRI FAQ][Fisheye vs Mirror Ball][Fisheye D-SLR Workflow Explained Visually][LDRI Reflections][Examples][HDRI Services]
HDRI for Film and Television Post Production.
Anyone that ever dealt with 3D before, knows how frustrating and time-consuming it can be to try and achieve a seamless integration between CGI and live action. There is finally a photographic technique that eliminates this age old problem, and it is called 'HDRI'.
HDRI FAQ (Frequently Asked Questions):
Nikon D200 D-SLR.
What is HDRI..?
HDRI stands for "High Dynamic Range Image". In short it is a specialized photographic technique that allows one to capture the exact lighting conditions and reflections on-set. By using HDRI maps in 3D software, one is able to seamlessly integrate computer generated objects into a live action environment, and thus achieve completely believable results. This is due to the fact that the correct lighting, highlights, contact shadows and reflections are contained in the HDRI photographs captured on-set during the live action shoot. The HDRI data can now be used in 3D to recreate the exact same lighting conditions that was present in the 'real world' at a specific moment in time. Realism is thus far easier to achieve in 3D, and seeing that one does not have to try and match the lighting conditions from scratch, HDRI dramatically cuts down on the lighting time in production.
How does HDRI work..?
The on-set lighting conditions are captured with a Fisheye lens (capable of taking 180 degree photographs). A HDRI photograph is unique in the fact that it stores both colour and intensity values of the environment, as the image integrates numerous exposures (camera stops) of the environment in one file at an extraordinary high colour depth and image resolution. This allows one to realistically control the lighting of computer generated objects in a real or 3D environment. In 'Old School' Post Production terms, the level of exposure control that HDRI offers in 3D, can be compared to the flexibility of grading 35mm film-stock in TeleCine.
How can we use HDRI in Post-Production..?
HDRI can be used in all the high-end 3D software packages today. Once the HDRI photographs are unwrapped and converted, it can be used in production, saving on 3D lighting and texturing time, and ensuring realistic results for film projects and high-end television commercials.
What is the process for HDRI generation on-set..?
When a commercial or film is being shot, about 5 minutes is required on-set (per scenario) to take the necessary photographs for HDRI generation. Only shots that require CGI integration into live action need HDRI maps, but HDRI can also greatly enhance completely computer generated scenes (see examples below).
Would HDRI work in a "Green-Screen" Studio scenario..?
Yes, it is still possible to extract the lighting and contact shadow information successfully. Seeing that the studio environment won't match the final surroundings that the "Green-Screen" footage will be composited into, the reflection information in the HDRI photographs will be incorrect. Depending on the requirements, a number of techniques can be used to remove or desaturate the "Chroma-Screens". It is also possible to light a 3D computer generated environment with the HDRI photographs, and then render new Fisheye images from within the 3D software. These images can then be combined with (or completely replace) the shot HDRI photographs, and will contain both the original "On-Set" HDRI lighting, and the correct reflection information from the 3D environment.
Typical Green-Screen studio shoot.
Master lighting HDRI Exposures (0.6 EV Steps).
"Green-Screen" Studio HDRI Examples.
Note: The Nikon 10.5mm Fishey does not suffer from traditional lens flare problems. Even when you take photographs directly into bright studio lights, large "Bag-O-Lights" (or the sun for that matter), the images are flare free due to the high quality ED lens elements.
What are the technical specifications of
the HDRI files that you will provide..?
The photographs are taken at 10.2 Megapixel (3872 x 2592 pixels) in uncompressed 12 bit per channel sRGB RAW format, on a professional Nikon D200 D-SLR (in Post Production terms, this resolution and colour depth is higher than required by Discreet Inferno for Full Frame Academy 2K Film resolution). The original high quality photographs can then be saved as 16 bit per channel Tiff files, converted to HDRI format (.hdr), or saved in any other image format that the Post Production House or Animation Studio might require. When a full 360 degree panorama is required, the final HDRI files can be generated at over 10000 pixels horizontal resolution (at 8 or 16 bit/channel colour).
Why I prefer using a Fisheye Lens, instead of a Mirror Ball:
Fisheye Lens versus Mirror Ball:
You can generate HDRI images by photographing the reflections in a Mirror Ball, or using a Fisheye lens. Mirror Balls are used more frequently, due to the low cost of a chrome bearing (or reflective Christmas tree decoration), compared to the hefty price tag of a professional D-SLR Camera and a prime Fisheye lens. A good Fisheye lens on a new generation D-SLR Camera (like the Nikon D70) has a lot of obvious advantages.
Fisheye HDRI Benefits:
* The photographer and tripod doesn't reflect into the Mirror Ball, and thus don't need to be painted out.
* The image doesn't contain the dents, scathes and imperfections of a Mirror Ball reflection.
* The image doesn't have to be unwrapped from a ball, which eliminates resolution problems on the edges.
* The colour depth and superior image resolution is a clear advantage.
* The process is faster, and thus less irritating to the Director and crew On-Set.
About the Nikon AF DX Fisheye 10.5mm /
2.8 G Lens:
The Nikon DX Fisheye 10.5 mm lens is specifically designed for use with the new generation D-SLR cameras, and feature superb ED (Extra-low Dispersion) lens elements, which minimize Chromatic Aberration on the edges of the frame (an age old Fisheye Lens problem). Standard 16 mm SLR Fisheye lenses aren't able to produce a 180 degree field of view on D-SLR cameras, due to the fact that the CCD is smaller than a traditional SLR camera's 35mm film gate. The Nikon 10.5 mm lens compensates for the smaller CCD, and produces a full frame 180 degree photograph on a D-SLR camera. Seeing that the photograph is captured full frame (and not in a traditional circular Fisheye ball), greatly enhances the resolution and minimizes detail breakup when the image is unwrapped. Note from the included examples that undesirable lens flares are also not present when shooting directly into studio lights or the sun.
HDRI form Fisheye - Workflow Explained Visually:
> Click on images to Enlarge <
What a Fisheye photograph looks like on a professional D-SLR Camera:
The straight lines and geometric nature of architecture, clearly illustrates the Fisheye distortion.
Original Fisheye photograph (Nikon D70 D-SLR with Nikon DX Fisheye 10.5mm Lens).
Photograph Un-wrapped in Nikon Capture Software.
Photograph Un-distorted in Nikon Capture Software.
Bracketing Exposures for HDRI Generation.
In this example, I only required a 180 degree upper hemisphere HDRI dome. To achieve this, the camera is placed on a stable tripod (like a Manfrotto with a Geared Head for accuracy) looking straight up, and fired via IR Remote or a Laptop (to eliminate bumping the camera). Exposure bracketing now creates under exposed, correctly exposed, and over exposed versions of the environment (required for generating HDRI maps).
About Nikon's RAW NEF (Nikon Electronic
Format), and Digital DEE (Dynamic Exposure Extender):
The Nikon D70 D-SLR can capture photographs in RAW Format (Nikon Electronic Format). NEF format is ideal for HDRI photography, as the images are not compressed, and captured at an extraordinary colour depth and resolution. The histogram is packed with image information that is not even be visible in the original exposure. All the detail in the shadows and highlights can be extracted without any loss of image quality. Nikon's Digital DEE (Dynamic Exposure Extender) control can also over and under expose the image correctly by up to 2 stops, using the dense colour depth contained in the photograph. The "White Balance" of the images can also be changed to compensate for incorrect colour temperature that artificial lighting (like florescent, flash and tungsten light) can produce . The amount of control is so impressive, that it is unnecessary to use handheld ambient and spot light-meters. Colour temperature correction filters are also a thing of the past.
All of the above simply means that by shooting HDRI in RAW (NEF) format, one can correctly generate more exposures from the existing exposure bracketed photographs. This increases the accuracy and the amount of HDRI lighting control dramatically.
Note: The Nikon D70 D-SLR is able to shoot with custom curves for the best results in every scenario. One can for instance load a curve to raise the exposure by .3 EV (.3 of an exposure value or camera stop) without burning out highlights. It is also possible to shoot in Adobe RGB (instead of standard sRGB), as the colour range is far superior.
The following links show some of the flexibility of NEF photographs in Adobe Photoshop and Nikon Capture software.
[ NEF in Photoshop ] [ Adobe RGB Color Space ] [ 16 bit/channel in Photoshop ] [ Digital DEE in Nikon Capture ]
About 180 and 360 degree panoramas:
Exterior - 360 Degree Cubic QuickTime VR Panorama (548 Kb).
360 Degree Cubic QTVR Panorama at the Botanical Gardens close to my house - Quicktime VR (1.58 Mb).
Panorama at the Botanical Gardens close to my house.
Interior - 360 Degree Cubic QuickTime VR Panorama (416 Kb).
Panorama of the second floor entertainment area at "Ministry of Illusion".
For more on Quicktime VR, visit my Interactive QTVR Web Demo page.
360 Degree Cylindrical and Spherical Panoramic Maps.
360 Degree Cylindrical Panoramic Maps.
In most cases it is sufficient to only shoot a 180 degree upper hemisphere HDRI dome. This successfully captures the lighting from horizon to horizon. Bounced light and floor reflections can be extracted from the live action footage in the form of LDRI (Low Dynamic Range Images), various Raytracing techniques, and via 3D Camera Projection Mapping. In some cases it is however necessary to capture a complete 360 degree HDRI environment. This can be done by shooting sets of overlapping (exposure bracketed) HDRI photographs at calculated rotational increments. For the best results, this must be done with a specialized rotating tripod pan head, that is able to rotate around the nodal point of the lens (and not around the back of the camera body). The nodal point is the exact point in a lens were all light converges and flips over before reaching the CCD or film back. By correctly positioning the nodal point the effects of parallax is greatly minimized, as the nodal point of the lens will line with the center of panoramic rotation. The images can then be "Stitched" together to create a complete 360 degree HDRI lighting sphere or panorama. Through the techniques that I use, the final HDRI files can be generated at over 7000 pixels horizontal resolution at 16 bit/channel colour. Depending on the requirements, the results can be output as Cylindrical, Spherical or Cubical Maps for 3D.
Preparing the HDRI Images for 3D mapping:
Depending on the requirements, the HDRI map can now be warped to map correctly in 3D.
Longitude / Latitude Map (for 180 Degree Spherical Mapping).
Cubic Map (for 180 Degree Cubic Mapping).
HDRI can also provide Diffuse Maps (far left), and Specular Maps (middle) for addition lighting control. By combining this with an Ambient Occlusion pass (to restore the shadow areas), great realism can be achieved.
Mapping the HDRI Environment in Maya:
The HDRI map can now be mapped in Maya (and most other 3D packages). Instead of trying to match the lighting artificially in 3D, the HDRI map is now used to achieve the correct lighting, contact shadows and reflections. As a result, the on-set lighting conditions can now be recreated in 3D, allowing a seamless integration between 3D and live action. The correct exposure and shadow intensity can be achieved (and correctly interpreted by the renderer), as all the data of the exposure bracketing is available in 3D.
Shaded view from under the HDRI Environment Dome in Maya (180 degrees, horizon to horizon).
A picture is worth a 1000 words, so lets look at the results. For this example, I especially chose the most obvious and overused computer graphics subject matter. If one can make a simple sphere look good, it is easy to see the possibilities of a detailed realistic model in a real (or computer generated) environment. This image was rendered in MentalRay (Maya 6.0) with standard (basically un-tweaked) Lambert and Blinn Shaders. The Bump Maps are standard Fractal Textures, and all MentalRay and Final Gathering settings were on the Maya defaults (and thus renders fast).
The Rendered HDRI Image (using the interior HDRI Map shown above).
Caustic Render Pass for the Glass Ball.
The Final Result (An additional Depth pass will add even more realism).
Exactly the same scene and shaders (only the HDRI Maps were changed).
LDRI (Low Dynamic Range Images) Reflections:
Here are LDRI (non-bracketed) examples of a 360 degree Environment Sphere. The renders were done in MentalRay for Maya with default settings. The background is a Cylindrical map that was generated form the panoramic photographs. A Blinn Shader reflects the 360 degree LDRI Spherical Environment. In these examples the objects only reflect the environment, and don't reflect back into each other. The combination of LDRI and limiting the amount of reflections, can give good results in a fraction of the time.
Jpg DivX Movie - 4.83 Mb. 360 QTVR Thumbnail - 85 Kb.
Jpg DivX Movie - 5.44 Mb. 360 QTVR Thumbnail - 108 Kb.
HDRI Project Examples:
HDRI for "Number 10" Feature Film:
CGI Crowds - Making 80 000 people.
Film - No 10- Making Of (32.32 Mb Quicktime 7 - H.264 Codec - 640 x 480 pixels)
3D VFX Supervisor at Ministry of illusion, Vicon Motion Capture, Crowd Simulation, HDRI and Match-Moving.
No 10 Movie Trailers:
[ Bridge Teaser ] [ Celebration Teaser ] [ Rrugby Teaser ] [ Number 10 trailer ]
HDRI for "Toyota Fortuner" television commercial:
Job done as VFX Supervisor at Ministry of illusion.
TV - Toyota Fortuner - Making Of (17.7 Mb Quicktime 7 - H.264 Codec - 640 x 480 pixels)
VFX Supervision, On-Set HDRI, Match-Moving, Texturing and Lighting.
HDRI for "Outsurance" television commercials:
Cloth Simulation and HDRI..
TV - Outsurance"Cover" - Making Of (7.09 Mb Quicktime 7 - H.264 Codec - 640 x 480 pixels)
3D VFX Supervisor at Ministry of illusion, R&D, On-Set HDRI, Texturing, Lighting, Match-Moving & Syflex Cloth Simulation supervision.
HDRI for "Toyota Hilux Aliens" television commercial:
In collaboration with AnimMate.
TV - Toyota Hilux Aliens - Making Of (17.69 Mb Quicktime 7 - H.264 Codec - 640 x 480 pixels)
VFX Supervision, Vicon Motion Capture, HDRI, Digital Set Creation & Match-Moving.
In collaboration with AnimMate.
Final "Toyota Hilux - Aliens" TV Commercial (9.42 Mb - Divx Codec - 640 x 480 pixels)
Shot 1 Digital Environment Reconstruction (6.06 Mb - Divx Codec - PAL)
Quicktime VR (unedited panoramic - normal exposure for HDRI) (98 Kb Quicktime VR Codec -240 x 128 pixels)
Green-Screen HDRI for "Coca-Cola Collaboration" television commercial:
The HDRI was photographed on-set in a green-screen studio. The on-set prop was used as a visual guide for the completely computer generated environment.
3 Exposures (-2 <- 0 -> +2 Stops).
The Fisheye photograph at the correct (3D Matrix Metered) exposure.
The colour corrected HDRI interior (tweaked to match the Spirit DataCine Film grade).
The "Green-Screen" Studio HDRI photographs.
Examples of the Sound Booths in the "Coca-Cola Collaboration" television commercial.
The final "Coca-Cola Collaboration" television commercial.
DivX Codec - 384-288 pixels - MP3 16 Bit Stereo Audio - 9.51 Mb.
Note: Due to the tight deadline and limited rendering resources, only the Sound Booth interiors are "baked" HDRI.
All work on this site is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 2.5 License.
Freelance HDRI Services for Film and Television Post Production.
For more information, contact:
Martin Heigan (Freelance 3D Animator / VFX Supervisor).
Time Zone: GMT +2
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