Global Tone Research Articles

A Simple Algorithm for Managing Color in Global Tone Reproduction

Abstract Simple tone reproduction methods, such as the Reinhard global photographic tone-mapping operator, are popular methods for mapping high-dynamic range images to a low-dynamic range display. However, these methods deal mainly with how luminance is mapped; much less attention has been paid to how a full RGB color is produced. We introduce a simple method, inspired by traditional photography's use of polarizers to manage color, to map RGB colors when using global photographic operators for luminance. This method allows the user to trade off luminance for colorfulness, avoids unpredictable hue shifts and desaturation of the image, and guarantees that results lie in the RGB color cube without clamping.

Noise reduction in high dynamic range images

Multiple images with different exposures are used to produce a high dynamic range (HDR) image. Sometimes high-sensitivity setting is needed for capturing images in low light condition as in an indoor room. However, current digital cameras do not produce a high-quality HDR image when noise occurs in low light condition or high-sensitivity setting. In this paper, we propose a noise reduction method in generating HDR images using a set of low dynamic range (LDR) images with different exposures, where ghost artifacts are effectively removed by image registration and local motion information. In high-sensitivity setting, motion information is used in generating a HDR image. We analyze the characteristics of the proposed method and compare the performance of the proposed and existing HDR image generation methods, in which Reinhard et al.’s global tone mapping method is used for displaying the final HDR images. Experiments with several sets of test LDR images with different exposures show that the proposed method gives better performance than existing methods in terms of visual quality and computation time.

An Adaptive Tone Mapping Algorithm for High Dynamic Range Images

A common task of tone mapping algorithms is to reproduce high dynamic range images (HDR) on low dynamic range (LDR) display devices such as printers and monitors. We present a new tone mapping algorithm for the display of HDR images that was inspired by the adaptive process of the human visual system. The proposed algorithm is based on center/surround Retinex processing. Our method has two novel aspects. The input luminance image is first compressed by a global tone mapping curve. The curvature of the compression curve is adapted locally based on the pseudo-Hilbert scan technique, so it can provide a better overall impression before the subsequent local processing. Second, the local details are enhanced according to a non-linear adaptive spatial filter (Gaussian filter), whose shape (filter variance) is adapted to the high-contrast edges of the image. The proposed method takes advantage of the properties of both global and local processing while overcoming their respective disadvantages. Therefore, the algorithm can preserve visibility and contrast impression of high dynamic range scenes in standard display devices. We tested the proposed method on a variety of HDR images and also compared it to previous research. The results indicated that our method was effective for displaying images with high visual quality.

Tone-mapping high dynamic range images by novel histogram adjustment

In this paper, we present novel histogram adjustment methods for displaying high dynamic range image. We first present a global histogram adjustment based tone mapping operator, which well reproduces global contrast for high dynamic range images. We then segment images and carry out adaptive contrast adjustment using our global tone mapping operator in the local regions to reproduce local contrast and ensure better quality. We demonstrate that our methods are fast, easy to use and a fixed set of parameter values produce good results for a wide variety of images.

CIECAM02-based tone mapping technique for color image contrast enhancement

We propose a CIECAM02-based tone mapping technique for color image contrast enhancement that works especially well in bright surrounding conditions. The CIECAM02 is inherently strong when considering human visual systems (HVS) and surrounding conditions. In general, dark regions look darker in bright surrounding conditions, so some details in these dark regions tend to disappear. To overcome this problem, we propose a global tone mapping technique for color image contrast enhancement that uses a gamma encoding and the I/O relationship of the CIECAM02 in bright surrounding conditions. The proposed method makes the contrast of the source image stronger in bright surrounding conditions. We confirmed the superior performance of the proposed method in bright surrounding conditions by psychophysical experiment.

HDR Image Rendering by Combining Single-Scale Local and Global Tone Mapping Operators

HDR Image Rendering by Combining Single-Scale Local and Global Tone Mapping Operators

Human epididymal and prostatic tracts of vas deferens: Different contraction response to noradrenaline stimulation in isolated organ bath assay

In the present study epididymal and prostatic portions of human vas deferens were separately isolated and stimulated with exogenous noradrenaline to study their contractile properties. The results displayed that the epididymal tract produced a phasic–tonic response, while the prostatic strip produced only a phasic response suggesting a different functional role of each vas deferens segment. Moreover, it has been verified if α 1-adrenoceptor antagonists doxazosin, alphuzosin and terazosin could differently block the noradrenaline response in each segment. Doxazosin, the most potent antagonist, displayed similar potency in epididymal and prostatic tract (pA 2 = 8.51 and 8.42, respectively). Analogously, alphuzosin, although less potent than doxazosin, displayed in the same tracts a superimposed potency (pA 2 = 7.25 and 7.30, respectively). In contrast with doxazosin and alphuzosin, terazosin displayed higher potency in blocking the contractile response in prostatic tract (pA 2 = 7.67) than in epididymal segment (pA 2 = 6.43). These results showed that α 1-adrenoceptor antagonists doxazosin and alphuzosin, although with a different potency, did not discriminate between epididymal and prostatic segment while terazosin showed high potency in prostatic tract and only a moderate activity in epididymal section. Moreover, the biological model employed in our experiments could be a valid screening method to test the potential interferences of drugs indicated for bladder outlet obstruction with the peristaltic activity or the global tone of the human vas deferens.

Encoding of high dynamic range video with a model of human cones

A recently developed quantitative model describing the dynamical response characteristics of primate cones is used for rendering high dynamic range (HDR) video. The model provides range compression, as well as luminance-dependent noise suppression. The steady-state (static) version of the model provides a global tone mapping algorithm for rendering HDR images. Both the static and dynamic cone models can be inverted, enabling expansion of the HDR images and video that were compressed with the cone model.

Perception-motivated high dynamic range video encoding

Due to rapid technological progress in high dynamic range (HDR) video capture and display, the efficient storage and transmission of such data is crucial for the completeness of any HDR imaging pipeline. We propose a new approach for inter-frame encoding of HDR video, which is embedded in the well-established MPEG-4 video compression standard. The key component of our technique is luminance quantization that is optimized for the contrast threshold perception in the human visual system. The quantization scheme requires only 10--11 bits to encode 12 orders of magnitude of visible luminance range and does not lead to perceivable contouring artifacts. Besides video encoding, the proposed quantization provides perceptually-optimized luminance sampling for fast implementation of any global tone mapping operator using a lookup table. To improve the quality of synthetic video sequences, we introduce a coding scheme for discrete cosine transform (DCT) blocks with high contrast. We demonstrate the capabilities of HDR video in a player, which enables decoding, tone mapping, and applying post-processing effects in real-time. The tone mapping algorithm as well as its parameters can be changed interactively while the video is playing. We can simulate post-processing effects such as glare, night vision, and motion blur, which appear very realistic due to the usage of HDR data.

Improving the Retinex algorithm for rendering wide dynamic range photographs

Digital photography systems often render an image from a scene-referred description with very wide dynamic range to an output-referred description of much lesser dynamic range. Global tone maps are often used for this purpose, but can fail when called upon to perform a large amount of range compression. A luminance formulation of the Retinex ratio-reset-product-average algorithm produces a smoothly changing contrast mask of great benefit, but it too can fail where high contrast edges are encountered. A slight but critical modification to the Retinex equation - introducing a ratio modification operator - changes the nature of the generated contrast mask so that it is simultaneously smooth in regions of small contrast ratios, but extremely sharp at high contrast edges. A mask produced in this way compresses large and undesirable contrast ratios while preserving, or optionally enhancing, small ratios critical to the sensation of image contrast. Processed images may appear to have a greater contrast despite having a shorter global contrast range. Adjusting the new operator prior to processing gives control of the degree of compression at high contrast edges. Changing the operator during processing gives control over spatial frequency response.

A Study of Kono Tone Spacing

Abstract Measurements were made of the fundamental frequency of a register two-tone language, Kono, a Northern Mande language from the Niger-Congo group. This language has the tonal feature of downstep which conveys linguistic information in specific contexts and introduces a terracing effect on successive high tones. The physical values were converted into their musical scale equivalents and comparisons were made with a three-tone system. They were found to be different. Observations of local and global tone ranges were made and were discussed in terms of tone spacing.