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.
Conclusions
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.
Notes:
- 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."
Original images courtesy of Christian Bloch. All other content (c) 2008 MaxUnderground.
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