Since working with HDR images is comparable to working with light itself, we can use this property to illuminate CGI objects and simulate extremely accurate reflections to seamlessly blend 3D and 2D components together. The following example demonstrates what movie studios have been doing for years to create very realistic compositing scenes and effects.
We start out with a background plate, which was merged together from 8 different exposures. The location is DUMBO, Brooklyn—an area between the Brooklyn and Manhattan Bridges. The cobblestones and part of the original railroad track date back to the 19th century when the area was primarily populated with factories that made machinery, paper boxes, and Brillo soap pads.
Shooting directly into the sun and getting great local contrast and detail throughout the entire tonal range of the scene is an easy task for a 32–bit HDR file. Here, several adjustments were made to balance out light levels and emphasize warm late–afternoon sun.
At the same time we shot the background, we've also created a light probe—a 360–degree HDR panorama, which will be used to illuminate our CGI object. This one file contains all the information about the lighting conditions of this particular spot at this particular time of day. This will also be our source for creating very accurate and realistic surface reflections on the model. Below you see a tonemapped representation of this HDR file.
Next we place a Baureiche 52 German locomotive (WWII era) on the rails and match virtual camera's focal length and angle to the real one we used for the background shot to match the perspective.
In this render a polished stainless steel material was applied to the model to clearly demonstrate the effects of the HDR light probe, which now invisibly surrounds the model. Notice how the nose of the locomotive (the smoke box door) is accurately reflecting the buildings and the Manhattan Bridge which are behind the camera. Same reflection can also be seen on the buffer in front. The color palette comes from the light probe as well.
Here the final textures were applied to the model. The rusted metal is still showing some reflections to enhance realism. Also, the position and intensity of the sun were matched to create a streak of light across the side of the locomotive. Front lights were turned on and the render was saved as a 32–bit EXR file.
The final compositing was done in 32–bit mode as well. Only minor color tweaking was necessary to seamlessly blend the train with the background. The ground shadow was added along with the lens flare to tie everything together. A larger version of this final image is available in the gallery section to the left.
Using HDR images to accurately mimic real–world lighting conditions is a rather new development in the photography world. So far it has primarily been used in car advertising. Nonetheless, photographers from other disciplines (still–life, architectural, editorial) can benefit from this revolutionary technique. Possibilities of its application are only limited by one's creative abilities.
< back to introduction and chapters
All photographs © DOT Editions, 2008. All Rights Reserved.