Tone mapping

About: Tone mapping is a research topic. Over the lifetime, 1713 publications have been published within this topic receiving 48490 citations.

Testing tone mapping operators with human-perceived reality

Abstract: A number of successful tone mapping operators for con- trast compression have been proposed due to the need to visualize high dynamic range (HDR) images on low dynamic range (LDR) devices. They were inspired by fields as diverse as image process- ing, photographic practice, and modeling of the human visual sys- tems (HVS). The variety of approaches calls for a systematic per- ceptual evaluation of their performance. We conduct a psychophysical experiment based on a direct comparison between the appearance of real-world scenes and HDR images of these scenes displayed on an LDR monitor. In our experiment, HDR im- ages are tone mapped by seven existing tone mapping operators. The primary interest of this psychophysical experiment is to assess the differences in how tone mapped images are perceived by hu- man observers and to find out which attributes of image appearance account for these differences when tone mapped images are com- pared directly with their corresponding real-world scenes rather than with each other. The human subjects rate image naturalness, overall contrast, overall brightness, and detail reproduction in dark and bright image regions with respect to the corresponding real-world scene. The results indicate substantial differences in the perception of images produced by individual tone mapping operators. We ob- serve a clear distinction between global and local operators—in fa- vor of the latter—and we classify the tone mapping operators ac- cording to naturalness and appearance attributes. © 2007 SPIE and

Fast automatic compensation of under/over-exposured image regions

Abstract: This paper presents a new algorithm for spatially modulated tone mapping in Standard Dynamic Range (SDR) images. The method performs image enhancement by lightening the tones in the under-exposured regions while darkening the tones in the over-exposured, without affecting the correctly exposured ones. The tone mapping function is inspired by the shunting characteristics of the center-surround cells of the Human Visual System (HVS). This function is modulated differently for every pixel, according to its surround. The surround is calculated using a new approach, based on the oriented cells of the HVS, which allows it to adapt its shape to the local contents of the image and, thus, minimize the halo effects. The method has low complexity and can render 1MPixel images in approximately 1 second when executed by a conventional PC.

Face image acquisition method under uneven lighting condition

Abstract: The invention discloses a face image acquisition method under an uneven lighting condition. The face image acquisition method can obtain high-quality face images under the uneven lighting condition. According to the invention, an area of interest of a face contained in an image is divided into different illumination areas; the exposure time is adjusted as for the different illumination areas, and each illumination area is enabled to take the neutral brightness as the target exposure brightness, so that detail information of the different illumination areas when the face is under uneven lighting condition is obtained; and the high dynamic range synthesis is performed for obtained images of different exposure degrees, and the tone mapping technology is used to convert a high dynamic range image into a low dynamic range image which is easy to process and display by a computer. The method provided by the invention can effectively solves a problem that the quality of a face image is degenerated due to the uneven lighting condition, and the obtained high-quality face image is beneficial for subsequent image processing and machine visual sense analysis and the like.

Constant Bracket High Dynamic Range (cHDR) Operations

Abstract: Systems, methods, and computer readable media to capture and process high dynamic range (HDR) images when appropriate for a scene are disclosed. When appropriate, multiple images at a single—slightly underexposed—exposure value are captured (making a constant bracket HDR capture sequence) and local tone mapping (LTM) applied to each image. Local tone map and histogram information can be used to generate a noise-amplification mask which can be used during fusion operations. Images obtained and fused in the disclosed manner provide high dynamic range with improved noise and de-ghosting characteristics.

Hierarchical tone mapping for high dynamic range image visualization

Abstract: In this paper, we present a computationally efficient, practically easy to use tone mapping techniques for the visualization of high dynamic range (HDR) images in low dynamic range (LDR) reproduction devices. The new method, termed hierarchical nonlinear linear (HNL) tone-mapping operator maps the pixels in two hierarchical steps. The first step allocates appropriate numbers of LDR display levels to different HDR intensity intervals according to the pixel densities of the intervals. The second step linearly maps the HDR intensity intervals to theirs allocated LDR display levels. In the developed HNL scheme, the assignment of LDR display levels to HDR intensity intervals is controlled by a very simple and flexible formula with a single adjustable parameter. We also show that our new operators can be used for the effective enhancement of ordinary images.