GPU Gems

GPU Gems

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Part IV: Image Processing

When most people think of GPU power, they focus on purely 3D applications, yet the pictures we actually see on our monitors are 2D. Programmable pixel shaders provide personal computers with unprecedented image-processing power, extending our abilities for both 2D and 3D development.

Graphic designers and illustrators have long used complex controls in still-image photo-editing applications, but such programs can process only one picture at a time. The newest GPUs can perform these previously slow operations at interactive rates, allowing us to apply the full power of complex compositing and color-control applications not just to still images and layouts, but also to full-motion video and gameplay. Complex video coloring that previously required an entire suite of specialized equipment can now be done on a laptop PC.

Understanding color spaces is one aspect of image processing, whether we are mapping 2D images into new 2D images or rendering 3D scenes to the screen. Equally important is understanding how images of varying sizes and shapes can be filtered during manipulations to provide smooth, fast results. GPUs are capable of executing the same filtering algorithms as CPU-based image-processing tools, but they also can invoke new hardware-accelerated methods.

In Chapter 21, "Real-Time Glow," Greg James and John O'Rorke give us an example of how 3D gameplay can be enhanced with 2D image processing. By adding 2D lighting effects such as glows, they show how a little image processing can completely alter the feel and play-action of 3D imagery. Once you see how these results are accomplished, you may not be able to enjoy 3D imagery without them again.

In Chapter 22, "Color Controls," I extend the discussion of image processing in games to the uses and methods of technical and artistic color control, for moving imagery into and out of unusual color spaces, as well as quickly adding polished color-tuning to any scene, 2D or 3D. The colors we see in print and on television today are almost universally color-controlled. Developers should be able to understand and use the same tools for their game engines.

In Chapter 23, "Depth of Field: A Survey of Techniques," Joe Demers writes about using GPU operations to create depth-of-field effects in real time. By following a few simple filtering rules, developers can simulate the complex effects of real-world camera focusing, film saturation, and more on 3D models.

Chapter 24, "High-Quality Filtering," generalizes image filtering and effects to images of arbitrary size, applying the notion of filter kernels and analytic calculation to the problem of 2D and 3D antialiasing. Significantly, we can see that some "classical" antialiasing and filtering problems are best solved on the GPU by using hardware accelerations not typically available to CPU-based approaches.

Matt Pharr describes an unusual application of texturing in 2D space in Chapter 25, "Fast Filter-Width Estimates with Texture Maps." By cleverly manipulating the results of texture operations, he's able to determine local partial derivatives of complex functions, even when using hardware profiles that don't provide direct hardware support for these operations.

In Chapter 26, "The OpenEXR Image File Format," Florian Kainz, Rod Bogart, and Drew Hess of Industrial Light & Magic (ILM) describe the OpenEXR standard, a new, high-dynamic-range image format that's quickly spreading through the top tiers of motion-picture computer imaging. OpenEXR is a key tool for developers looking to exploit the new world of image-based lighting, and the ILM team shows how they've adopted GPU processing speed to make OpenEXR a valuable day-to-day tool at ILM—not just for 3D work, but also for image acquisition, compositing, and playback—again, in real time.

Of course, to apply these techniques requires the developer to manage image-processing tasks. In Chapter 27, "A Framework for Image Processing," Frank Jargstorff presents a scheme for 2D image processing that's flexible and applicable to a variety of applications. The framework can even be extended to mix GPU and CPU operations in a way that's fairly transparent to developers of games, photo applications, and video applications alike.

Kevin Bjorke, NVIDIA


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