11/6/2023 0 Comments Lut format![]() However, one may observe that no matter how complex the function, it can evaluate to only one of 255 output values (corresponding to each unique input). The naive implementation would be to step through the image and for each pixel to evaluate the function. Typically leveraging three LUTs-one for each color channel-these tables enable the computationally efficient modification of pixel intensity just before an image reaches the monitor.Ĭonsider an analytical color operator, f( x), applied to an 8-bit grayscale image. One-dimensional LUTs have long been utilized in image processing, most commonly in the form of the monitor gamma table. The identity lookup table is defined as the transform that maps the input index back to itself over a given domain, as shown in Figure 24-1.įigure 24-1 How One-Dimensional Lookup Tables Work The simplest LUTs are indexed by a single variable and thus referred to as one-dimensional (or 1D) LUTs. 24.1.1 One-Dimensional LUTsĪ lookup table is characterized by its dimensionality, that is, the number of indices necessary to index an output value. For data requests that fall between the table's samples, an interpolation algorithm can generate reasonable approximations by averaging nearby samples. If the table lookups can be performed faster than computing the results from scratch (or if the function is repeatedly queried at the same input), then the use of a lookup table will yield significant performance gains. By precomputing the evaluation of a function over a domain of common inputs, expensive runtime operations can be replaced with inexpensive table lookups. Lookup tables (LUTs) are an excellent technique for optimizing the evaluation of functions that are expensive to compute and inexpensive to cache. The techniques presented in this chapter, and variations thereof, have been successfully utilized in the production of numerous motion pictures and should be regarded as "production ready." 24.1 Lookup Table Basics Our approach offers excellent performance characteristics, being independent of both the number of color operators applied as well as the underlying color transform complexity. ![]() In this chapter, we present an algorithm that leverages three-dimensional lookup tables to enable the real-time color processing of high-resolution imagery. ![]() On the consumer side, enabling the real-time color correction of video and rendered image streams is becoming an increasingly useful tool to shape media's thematic "look." However, directly applying multiple sophisticated color transforms to high-resolution imagery is beyond the real-time capability of modern graphics hardware. In feature-film visual-effects production, maintaining interactive feedback of high-quality color operations is extraordinarily beneficial to an artist. Using Lookup Tables to Accelerate Color Transformations The CD content, including demos and content, is available on the web and for download.Ĭhapter 24. You can purchase a beautifully printed version of this book, and others in the series, at a 30% discount courtesy of InformIT and Addison-Wesley. GPU Gems 2 is now available, right here, online.
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