Greg Ward

High dynamic range display systems

The dynamic range of many real-world environments exceeds the capabilities of current display technology by several orders of magnitude. In this paper we discuss the design of two different display systems that are capable of displaying images with a dynamic range much more similar to that encountered in the real world. The first display system is based on a combination of an LCD panel and a DLP projector, and can be built from off-the-shelf components. While this design is feasible in a lab setting, the second display system, which relies on a custom-built LED panel instead of the projector, is more suitable for usual office workspaces and commercial applications. We describe the design of both systems as well as the software issues that arise. We also discuss the advantages and disadvantages of the two designs and potential applications for both systems.

High dynamic range imaging

Current display devices can display only a limited range of contrast and colors, which is one of the main reasons that most image acquisition, processing, and display techniques use no more than eight bits per color channel. This course outlines recent advances in high-dynamic-range imaging, from capture to display, that remove this restriction, thereby enabling images to represent the color gamut and dynamic range of the original scene rather than the limited subspace imposed by current monitor technology. This hands-on course teaches how high-dynamic-range images can be captured, the file formats available to store them, and the algorithms required to prepare them for display on low-dynamic-range display devices. The trade-offs at each stage, from capture to display, are assessed, allowing attendees to make informed choices about data-capture techniques, file formats, and tone-reproduction operators. The course also covers recent advances in image-based lighting, in which HDR images can be used to illuminate CG objects and realistically integrate them into real-world scenes. Through practical examples taken from photography and the film industry, it shows the vast improvements in image fidelity afforded by high-dynamic-range imaging.

JPEG-HDR: a backwards-compatible, high dynamic range extension to JPEG

The transition from traditional 24-bit RGB to high dynamic range (HDR) images is hindered by excessively large file formats with no backwards compatibility. In this paper, we demonstrate a simple approach to HDR encoding that parallels the evolution of color television from its grayscale beginnings. A tone-mapped version of each HDR original is accompanied by restorative information carried in a subband of a standard output-referred image. This subband contains a compressed ratio image, which when multiplied by the tone-mapped foreground, recovers the HDR original. The tone-mapped image data is also compressed, and the composite is delivered in a standard JPEG wrapper. To naive software, the image looks like any other, and displays as a tone-mapped version of the original. To HDR-enabled software, the foreground image is merely a tone-mapping suggestion, as the original pixel data are available by decoding the information in the subband. Our method further extends the color range to encompass the visible gamut, enabling a new generation of display devices that are just beginning to enter the market.

Automatic High-Dynamic Range Image Generation for Dynamic Scenes

Automatic high-dynamic range image generation from low- dynamic range images offers a solution to conventional methods, which require a static scene. The method consists of two modules: a camera-alignment module and a movement detector, which removes the ghosting effects in the HDRI created by moving objects.

54.2: A High Dynamic Range Display Using Low and High Resolution Modulators

We have developed an emissive high dynamic range (HDR) display that is capable of displaying a luminance range of 10,000cd/m2 to 0.1cd/m2 while maintaining all features found in conventional LCD displays such as resolution, refresh rate and image quality. We achieve that dynamic range by combining two display systems — a high resolution transmissive LCD and a low resolution, monochrome display composed of high brightness light emitting diodes (LED). This paper provides a description of the technology as well as findings from a supporting psychological study that establishes that correction for the low resolution display through compensation in the high resolution display yields an image which does not differ perceptibly from that of a purely high resolution HDR display.

Ldr2Hdr: on-the-fly reverse tone mapping of legacy video and photographs

New generations of display devices promise to provide significantly improved dynamic range over conventional display technology. In the long run, evolving camera technology and file formats will provide high fidelity content for these display devices. In the near term, however, the vast majority of images and video will only be available in low dynamic range formats. In this paper we describe a method for boosting the dynamic range of legacy video and photographs for viewing on high dynamic range displays. Our emphasis is on real-time processing of video streams, such as web streams or the signal from a DVD player. We place particular emphasis on robustness of the method, and its ability to deal with a wide range of content without user adjusted parameters or visible artifacts. The method can be implemented on both graphics hardware and on signal processors that are directly integrated in the HDR displays.

Subband encoding of high dynamic range imagery

The transition from traditional 24-bit RGB to high dynamic range (HDR) images is hindered by excessively large file formats with no backwards compatibility. In this paper, we propose a simple approach to HDR encoding that parallels the evolution of color television from its grayscale beginnings. A tone-mapped version of each HDR original is accompanied by restorative information carried in a subband of a standard 24-bit RGB format. This subband contains a compressed ratio image, which when multiplied by the tone-mapped foreground, recovers the HDR original. The tone-mapped image data may be compressed, permitting the composite to be delivered in a standard JPEG wrapper. To naive software, the image looks like any other, and displays as a tone-mapped version of the original. To HDR-enabled software, the foreground image is merely a tone-mapping suggestion, as the original pixel data are available by decoding the information in the subband. We present specifics of the method and the results of encoding a series of synthetic and natural HDR images, using various published global and local tone-mapping operators to generate the foreground images. Errors are visible in only a very small percentage of the pixels after decoding, and the technique requires only a modest amount of additional space for the subband data, independent of image size.The transition from traditional 24-bit RGB to high dynamic range (HDR) images is hindered by excessively large file formats with no backwards compatibility. In this paper, we propose a simple approach to HDR encoding that parallels the evolution of color television from its grayscale beginnings. A tone-mapped version of each HDR original is accompanied by restorative information carried in a subband of a standard 24-bit RGB format. This subband contains a compressed ratio image, which when multiplied by the tone-mapped foreground, recovers the HDR original. The tone-mapped image data may be compressed, permitting the composite to be delivered in a standard JPEG wrapper. To naïve software, the image looks like any other, and displays as a tone-mapped version of the original. To HDR-enabled software, the foreground image is merely a tone-mapping suggestion, as the original pixel data are available by decoding the information in the subband. We present specifics of the method and the results of encoding a series of synthetic and natural HDR images, using various published global and local tone-mapping operators to generate the foreground images. Errors are visible in only a very small percentage of the pixels after decoding, and the technique requires only a modest amount of additional space for the subband data, independent of image size.

II.5 – REAL PIXELS

Publisher Summary This chapter analyzes the concept of real pixels. It discusses a floating point format that only requires 32 bits per pixel and is completely portable between machine architectures. The idea is using an 8-bit mantissa for each primary and following it with a single 8-bit exponent. In most floating point formats, the mantissa is normalized to lie between .5 and 1. Because this format uses the same exponent for three mantissas, only the largest value is guaranteed this normalization, and the other two may be less than .5. It appears that this format favors the largest primary value at the expense of accuracy in the other two primaries. This is true, but it is also true that the largest value dominates the displayed pixel color so that the other primaries become less noticeable. The 32-bit real pixel format presented in the chapter preserves the bits that are most significant, which is the general goal of any floating point format. The chapter highlights that besides the ability to perform more general image processing without losing accuracy, real pixels are great for radiosity and other lighting simulation programs, because the results can be evaluated numerically well outside the dynamic range of the display.

Photometric image processing for high dynamic range displays

Many real-world scenes contain brightness levels exceeding the capabilities of conventional display technology by several orders of magnitude. Through the combination of several existing technologies, new high dynamic range displays have been constructed recently. These displays are capable of reproducing a range of intensities much closer to that of real environments. We present several methods of reproducing photometrically accurate images on this new class of devices, and evaluate these methods in a perceptual framework.

Practical global illumination with irradiance caching

Since its invention 20 years ago, irradiance caching has been successfully used to accelerate global illumination computation in the Radiance lighting simulation system. Its widespread use had to wait until computers became fast enough to consider global illumination in production rendering. Since then, its use is ubiquitous. Virtually all commercial and open-source rendering software base the global illumination computation upon irradiance caching. Although elegant and powerful, the algorithm often fails to produce artifact-free images. Unfortunately, practical information on implementing the algorithm is scarce. The objective of the class is twofold. The first and main objective is to expose the irradiance caching algorithm along with all the details and tricks upon which the success of its practical implementation is dependent. Various image artifacts that the basic algorithm can produce will be shown along with a recipe to suppress them. We will also put strong emphasis on practical aspects of irradiance caching integration in production environments and discuss the particularities used in two big production houses, namely PDI/DreamWorks and Pixar. The second objective is to acquaint the audience with the recent research results that increase the speed and extend the functionality of basic irradiance caching. Those include: exploiting temporal coherence to suppress temporal flickering; extending the caching mechanism to rendering glossy surfaces; accelerating the algorithm by porting it to the GPU. Advantages and disadvantages of those methods will be discussed.