The HDRI Handbook review
HDRI has become a familiar term for most CG artists. If you are reading this, chances are you are already using HDR images in your work and have probably seen your share of related tutorials on the net. So after learning that a new book on the subject has been released the logical question arises: what does The HDRI Handbook have to offer to further your knowledge in the HDRI front? A short but accurate answer: a lot.
Christian Bloch’s book combines detailed explanations of concepts behind HDR imaging with hands-on, step-by-step examples on how to apply that knowledge to your work. This proves to be a useful approach: the theory part contains many eye-openers (even for experienced CG artists), and the tutorials provide practical, real-life examples, while also offering many tips on how to obtain the best possible results. What are the pros and cons that the various HDRI formats have to offer? What is the best way to capture a panoramic HDRI? Do you really think you’re shooting that mirror-ball right? Think again.
Inside “The HDRI Handbook”
The book is divided into seven chapters:
A tone mapped version of an HDR image shows details in highlights and shadows
1. The Background Story – The first chapter lays down the basic concepts for understanding high dynamic range imaging: from exposure values to the human eye’s non-linear response to light, the ideas described in this chapter provide a clear explanation of what high dynamic range imaging is and why we should start making the move today towards an HDR future. A concise description of gamma encoding, and what it means for digital imaging is also included.
2. New Tools – This chapter charts the map of current HDR image formats as well as the software available for working with HDR images. It also provides a window onto HDRI history: Greg Ward, Paul Debevec, Florian Kainz, Helmut Dersch, Maryann Simmons, their work and contributions show up here. Still, the focus is on practical information: which format provides the lowest file size? What are the main advantages offered by OpenEXR? Is HDR-JPG the way to go?
3. Capturing HDR Images – Provides interesting information on image sensors and explains in great detail how to capture quality HDR images with currently available technologies. A step by step tutorial on merging LDR images into an HDR image (in various applications) shows how to obtain the final prize, and a list of tips for inspecting the quality of an HDR image helps develop a critical eye.
4. Tone Mapping – Examines the process of fitting an HDR image into an LDR image by reducing its dynamic range, while retaining details in highlights and shadows. Global and local operators are discussed as well as the various possible uses of tone mapping (“true tone mapping”, “new impressionism” and “texture extraction for CG” – as categorized by Mr. Bloch). This chapter also offers an unexpected treasure: two complete sections written by professional photographers Uwe Steinmüller and Dieter Bethke. These sections offer invaluable insights into how seasoned photographers are using HDR techniques for producing quality images. Some case studies that deal with common issues such as problematic interiors, night shots and scenes with strong backlighting are discussed thoroughly.
5. HDR Image Processing – Shows the many benefits that an HDR workflow brings to image processing and editing. Practical examples are given on how common Photoshop tools become much more useful thanks to editing in HDR mode, as well as how it affects the behavior of filters, which produce more natural results.
An HDR workflow brings image editing to the next level – one of the many tutorials featured in the book
6. Shooting Panoramic HDR Images – Covers the basics of panoramic photography and goes in-depth into the various methods for capturing panoramas: one shot, using a mirror ball (with a step-by-step tutorial on how to get the best results), segmental capture and skydomes. This chapter provides a lot of useful information for capturing environments that can be later used in CG, and also for panoramic photography in general. One of the best chapters in the book.
7. Applications in CGI – This is probably what you are looking for, so let’s spend a bit more time on this one. A few pages are dedicated to explaining the basics of CG rendering and lighting, then it quickly moves on to more advanced subjects. There’s a very clear explanation of how gamma correction affects 3D renderings, and which parts of the process should be modified when working with HDR images (“Linear Workflow” vs. “Cheater’s Workflow”). A section is dedicated to compositing and using render passes as an aid in achieving photorealism, with some welcome tips (though it focuses on a pure 3D scene, not on integrating 3D elements with a photographic image, which would have been more in line with the subject at hand). Image-based lighting using HDR images is then discussed in detail, as well as the principles for creating these setups in 3D applications. The book also comes with a companion DVD that contains a program called Smart IBL (i.e. the Smart Image-Based Lighting system), which automates the process of creating such setups. Smart IBL is a great time-saver that makes the components of an HDR lighting system available for any given scene at the click of a button. A convenient script is available for Max, as well as any other major 3D software, which automates the needed tasks for importing maps and setting up the basics of the scene (see Notes). The Smart IBL software comes with a sample collection of sIBL sets (which includes 20 HDR panoramas), and of course allows you to create your very own: it will take a high-res HDR image provided by the user, scale it down a bit and save it as a reflection map, tone map the original image for use as background and save it as a high-res LDR image, and finally resize and blur the original and save it as the environment lighting image. The Smart IBL editor even allows you to choose the format of the images it will output and make some relevant adjustments (such as shifting the UV coords of all associated maps at the same time, automatically guess the position of the sun so the sIBL Loader script creates a light source at that location, and more). Finally, other possible creative uses for HDR lighting are briefly covered, such as capturing the characteristics of a real lamp and using the resulting HDR image for lighting a scene.
The tutorials presented in the book are easy to follow and their results can be replicated using the corresponding sample files provided in the accompanying DVD. Concepts are explained clearly and the writing style helps make potentially dry subjects both interesting and enjoyable to read. This is quite an accomplishment in itself, especially considering The HDRI Handbook is at least partially based on the diploma thesis the author wrote while finishing his studies at the University of Applied Sciences Leipzig.
Mr. Bloch has also created a website at HDRLabs.com, where visitors can find the latest news on the HDRI front, the most recent versions of the sIBL software (yes, they are all freely available for download), discussion forums on all things HDRI, and more.
SIGGRAPH panoramas can help you light your scenes, thanks to sIBL
So what’s missing from The HDRI Handbook? The strength of the 3D application-independent approach implemented in the last chapter has pros, but it also has cons. It leaves some information missing for Max users (as well as users of other applications), namely how to use the various parameters available for tweaking image maps and light sources from inside 3DS Max in order to make the lighting components match a photographic background. Max users will have to make that final jump themselves, and for those who are not experienced in this regard, it will probably make them feel like they’re still standing a few steps away from crossing the image-based lighting bridge. Some of this information can be found scattered in tutorials around the net and in the Max 2009 help file. But a 3DS Max book dedicated to the subject is, surprisingly, still waiting to be written.
Also of note, one must take into account that HDR imaging is an emerging field. Certain parts of the book are bound to become outdated in the not too distant future. Mr. Bloch knows this, and has created his website as a way of expanding the content available in the book, so that readers can keep up with the latest developments and updates on HDRI matters. Most of the principles detailed in the book, however, should remain useful for years to come.
HDR technology is here to stay. Its advantages will no doubt displace film as the medium of choice for recording quality motion pictures (at last!), and will sooner than later spread into all types of software and hardware applications. The HDRI Handbook gives a solid theoretical background for understanding how it works, covers a wide range of practical uses, and provides a window to future developments. If you are looking for step-by-step instructions on using HDRI in Max, you will not find that content here. If you want to learn more about HDRI technology, and get an in-depth grasp of its practical applications in photography and CG, this is an excellent book to read and to keep on hand for continued reference.
- As of this writing the script for importing sIBL sets into Max works better with certain renderers than others. It’s advisable to download the script and try it out, and in case it fails, inspect the code to see if your renderer is included. Scripts are available at: http://www.hdrlabs.com/sibl/loader.html
- A word straight from the author on the subject above: “The MAX script is Open Source, and if someone can enhance the code, please please please say Hi in our forum so we can put the enhancements in the official distribution.”
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Original images courtesy of Christian Bloch.