Tone mapping

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

Tone Mapping Operators on Small Screen Devices: An Evaluation Study

Abstract: In the last decade, an increasing number of techniques have been developed to reproduce high dynamic range imagery on traditional displays. These techniques, known as Tone Mapping Operators (TMOs), have been compared and ranked in different ways according to several image characteristics. However, none of these algorithms has been developed specifically for small screen devices (SSD). In this paper, we present an evaluation of currently used TMOs to show that SSDs with limited size, resolution and colour depth require specific research to find or create an appropriate solution. The research described in this paper is based on psychophysical experiments; using three different types of displays (CRT, LCD and SSD). The obtained results show that rankings obtained are similar for the LCD and CRT but are significantly different for the SSD. Furthermore, these rankings show additionally that some characteristics of TMOs need to be emphasized to obtain better high-fidelity mapped images for SSDs.

Method for tone mapping based on histogram equalization

Abstract: The invention discloses a method for tone mapping based on histogram equalization. The method comprises the steps of: 1) inputting a high-dynamic range image; 2) acquiring the image brightness and converting the image brightness into a log domain; 3) carrying out histogram statistics; 4) calculating the average brightness of the image, and carrying out segmentation on the histogram by taking the average brightness as a segmentation point; 5) carrying out differentiation setting on mapping parameters of two segments of the histogram; 6) carrying out a histogram equalization algorithm in a segmentation mode; 7) restoring a brightness channel after the tone mapping to an RGB color space; and 8) outputting a displayable low-dynamic range image. According to the invention, the differentiation setting is carried out on the mapping parameters of the two segments after the histogram is segmented, and a bright background is enabled to map linearly as far as possible so as to reduce missing of a highlight part, and a foreground part is still subjected to histogram equalization processing so as to expand the contrast ratio of the image. The method disclosed by the invention can effectively maintain the original brightness of the image while increasing the contrast ration of the image, and effectively improves a phenomenon of brightness saturation in a classical histogram equalization algorithm.

On the perceptual similarity of realistic looking tone mapped High Dynamic Range images

Abstract: High Dynamic Range (HDR) images are usually displayed on conventional Low Dynamic Range (LDR) displays because of the limited availability of HDR displays. For the conversion of the large dynamic luminance range into the eight bit quantized values, parameterized Tone Mapping Operators (TMO) are applied. Human observers are able to optimize the parameters in order to get the highest Quality of Experience by judging the displayed LDR images on a realism scale. In the study presented in this paper, two TMOs with three parameters each were evaluated by observers in a subjective experiment. Although the chosen parameter settings vary largely, the chosen images appear to have the same QoE for the observers. In order to assess this similarity objectively, three commonly used image quality measurement algorithms were applied. Their agreement with the preference of the observers was analyzed and it was found that the Visual Difference Predictor (VDP) outperforms the Structural Similarity Index and the Root Mean Square Error. A threshold value for VDP is derived that indicates when two LDR images appear to have the same Quality of Experience.

Impact of temporal coherence-based Tone Mapping on video compression

Abstract: Tone Mapping Operators (TMOs) aim at converting real world high dynamic range (HDR) images captured with HDR cameras, into low dynamic range (LDR) images that can be displayed on LDR displays Even though most of the designed solutions provide good results for still HDR images, they are not efficient for tone mapping video sequences The main issue is their inability to preserve the temporal correlation inherent in a video sequence This has a consequence on the video compression efficiency In this work, we show that higher compression ratios can be obtained by preserving the temporal coherency of a sequence We evaluate temporal coherency and video compression in regard to two aspects The first one evaluates the quality of the decoded LDR sequences after applying different TMOs The second aspect assesses the quality of a reconstructed HDR sequence when a TMO and a codec are applied