Tone Reproduction Curve Research Articles

A method of tone reproduction curves computation by means of gradation trajectories in the form of Bézier curves

Tone reproduction curves (TRCs) have long been the basis for color adjustment in printing systems. Moreover, new algorithms for their processing and calculation, including tone value increase (TVI)‐based ones, are being constantly proposed. However, due to the fact that TRCs are just one‐dimensional curves covering only one colorant, they are not able to produce an exact match of all colors. Color adjustment with the help of the TRC is unstable, that is, a slight change in one color channel has a dramatic effect on the color reproduction in output. The use of gradation trajectories (GT) as an analytical model within the CIE Lab color space describing the behavior of the entire color gamut of the reproduction device makes it possible to more accurately adjust the individual color channel. Describing GT using the parametric Bézier curves further simplifies this process. In this work, we use GT to fit the TRC/TVI with the parameters recommended by ISO 12647‐2:2013.

Determining the ideal initial printing colorants in electrophotography by the discrete gradation trajectories

The accuracy and repeatability of the color reproduction in print is determined by the fine‐tuning of the tone reproduction curves of the basic printing colorants (most often this is CMYK). However, the diversity of manufacturers of printing equipment and dyes introduces an element of significant uncertainty about color uniformity. In addition, the traditional approach does not take into account the effect of hue change when applying the original dyes, as well as the nonlinearity of the hue rise in high‐ and low‐density areas. Determining the color of base colorants that produces the most uniform tone change is an important engineering challenge. Previously, there was no scientific basis for such calculations. We recently proposed an alternative color correction model based on gradation trajectories as an analogue of gradation curves in the CIE Lab space. We have also described the extension of the approach to double color overlay (gradation surfaces) and its analytical and discrete implications. The trajectories are the geodetic lines on gradation surfaces. In this paper, we propose using the gradation trajectories to determine “ideal” or “true” initial printing dyes for electrophotography. To simplify calculations, natural color discretization in digital printing is used.

Image quality evaluation for OLED-based smart-phone displays at various lighting conditions

The image quality of three organic light-emitting diode (OLED) based smart-phone displays was assessed at three levels of ambient lighting conditions corresponding to the darkroom, indoor and outdoor environment, respectively. Seven perceptual attributes, i.e., naturalness, colorfulness, brightness, contrast, sharpness, preference, and overall image quality (IQ), were evaluated in both standard dynamic range (SDR) and high dynamic range (HDR) mode via psychophysical experiments by rank order method, while readability was assessed only in SDR mode and gradation was investigated only in HDR mode. The experimental results demonstrate that, besides the color gamut, the tone reproduction curve is also an important factor affecting the colorfulness of mobile display in the two modes. Higher peak luminance would not mean better performance on brightness and contrast for HDR images, which is opposite to SDR mode. Further analysis of variance (ANOVA) indicates that the ranking results of all perceptual attributes are not significantly affected by the ambient lighting levels in both SDR and HDR modes.

Gray Balance Adjusting in Electrophotography by Means of Discrete Geodesics of Gradation Surfaces

Gray balance is one of the key issues of color balance and color appearance adjustment during printing. It takes into account the overlap of two or more colorants to achieve a visually neutral tone. It works in parallel with the adjustment of the main color channels. In electrophotography, the setting of color channels separately is usually carried out using tone reproduction curves. However, this traditional approach does not take into account the effect of changes in shades caused by their overlapping, We previously suggested using gradation trajectories (an analogue of tone reproduction curves in CIE Lab space) as an alternative paradigm for color channel adjustment. Further, we expanded the idea to the gradation surfaces as an expression of binary overlays. We proposed both analytic and discrete approaches to the computation of gradation trajectories and surfaces. The computations use the mathematical apparatus of differential geometry of spatial curves and surfaces. Discretization uses color quantization in digital printing devices and means that color coordinates are considered as continuous functions of filling a discrete raster cell with dyes. The color space metric is determined by the value of the CIE dE color difference. As gradation trajectories, we apply the discrete type of geodesic lines on the gradation surfaces of the corresponding binaries. In this work, we suggest using gradation surfaces in discrete form as a mathematical model of double dye overlays to adjust the gray balance in electrophotography.

Tone Reproduction Curve: rendering intents and their realization in halftone printing

Approaches to determining the Tone Reproduction Curve (TRC) which provides the reliable transfer of visual information in typical conditions of the halftone gray scale compression in relation to dynamic range of a graphic original or input image file are overviewed. The issues of such curve realization are also analyzed with taking into account the specifics of multiple stages of illustrative printing technology.

Basic Mathematics of Color Space Invariants

Color management in printing processes has been traditionally based on an analysis of the behavior of tone reproduction curves (TRC) calculated for the initial color channels. The tone curves, as well as, the color channels, are considered separately. This approach does not take into account the mutual influence of colorants when they overlap. We propose replacing two-dimensional tone reproduction curves with three-dimensional gradation trajectories in the CIE Lab metric space. When two colors overlap, one considers the space between two gradation trajectories that forms a gradation surface. These objects are described using the apparatus of differential geometry of spatial curves and surfaces, respectively, and are also invariants of color spaces. In this paper, we offer their analytical description.

Intelligent Image Rendition

The traditional image rendition process assumes an ideal output imaging system where each image pixel will be perfectly reproduced regardless of different image formation processes. In reality, each individual imaging system can be approximated as a linear system with its own unique transfer function characteristics, which could exhibit spatial and/or temporal variations. Consequently, it will produce inconsistent tone scale reproduction curves during the print production run. The objective of this paper is to investigate the tone reproduction curve variations caused primarily by the interaction of neighboring imaging pixels. An intelligent image rendition algorithm is presented to compensate for this macroscopic imaging process deficiency. Experimental results will be demonstrated to show the effectiveness of the proposed algorithm, which has been deployed commercially on a digital printing press.

AN IMPROVED HDR IMAGE PROCESSING USING FAST GLOBAL TONE MAPPING

People always try to reconstruct images that look like original scene. But it is not succeeded up to the expected level because the display devices cannot accommodate the actual r ange of illumination. The original scene is having high dynamic range (HDR) and the display devices are having low dynami c range (LDR) of values. Tone mapping can be used t o display HDR image in an LDR device. In this paper we are trying to de velop a better tone mapping method. A number of i mages with different exposure are fused to form an HDR image.. Here we u sed average method for this which is the simplest o ne. Then by using tone mapping the HDR image is converted into LDR. We tri ed Tone Reproduction Curve (TRC) based global tone mapping. TRC method results faster operation The global tone map ping operator algorithm is simple and does not int roduce ghosting. The image will also free from blur and halo like artifa cts. We took log average of the images to keep the pixel values within limit.

Lattice-Based $n$-Point Time-Sequential Sampling and Two-Stage Process Control for Maintaining Tone Consistency of Xerographic Processes

This paper proposes: 1) a lattice based time-sequential sampling approach that requires the printing and measuring of the smallest number of tonal samples to characterize the high-dimensional tone reproduction curve (TRC) at each print cycle, and 2) based on this characterization, the design of a two-stage control strategy to maintain tone consistency of a xerographic printing process. The printer's TRC maps the desired tones to the actual printed tones and it is high dimensional due to the large number of desired tones. To avoid using many sensors, the measurement of the TRC is achieved by sampling it time-sequentially and by reconstructing the TRC from the samples via a Kalman filter. In time-sequential sampling, only a few distinct <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$n$</tex></formula> tones are printed and measured at each print cycle. Using a lattice-theoretic framework, an optimal time-sequential sampling sequence with <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$n=1$</tex></formula> is designed. This is then extended to the case of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$n&gt;1$</tex></formula> to enable the tradeoff between sampling time and sampling resources. With the reconstructed time-varying TRC, a two-stage control strategy uses both the physical xerographic and the image processing processes to compensate for the TRC variations from the desired TRC. Simulations and experiments show that the proposed TRC stabilization system is effective for practical implementation. By stabilizing all the cyan, magenta and yellow primaries of the color xerographic print system, color consistency can be maintained. Furthermore, the proposed time-sequential sampling approach with <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$n=1$</tex></formula> exceeds the capability of conventional three-fixed-point sampling (light, middle, and dark tones) approach while requiring three times fewer samples.

30.3: Comparison of On‐Screen Display‐based and ICC Profile‐based Calibration for OLED Displays

AbstractThe tone reproduction curves of an OLED display were measured and modeled as a function of three on‐screen display (OSD) settings. The optimal OSD settings, derived from the model, outperformed two ICC profile‐based color calibration kits by reducing the calibration errors from 2.89% to 0.25% and the quantization errors from 9.28% to 0%.

Model-Based Calibration Approach to Improve Tone Consistency for Color Electrophotography

This paper aims to improve tone consistency for color electrophotography (EP). Color accuracy is crucial for printing. Calibrations are performed in EP printers to maintain consistent tone reproduction curves (TRCs). The calibration performance directly impacts the quality of color rendering. In this study, a model-based calibration approach is proposed to stabilize the TRCs. Regression models are developed to predict the primary color TRCs based on operating conditions and/or on-board sensor measurements. During a calibration, TRCs are predicted by the regression models, and the deviation is compensated by adjusting EP control parameters and modifying the tone correction mapping. The effectiveness of the proposed approach is validated using an off-the-shelf in-line four color EP printer under various environmental conditions and consumable factors. The experimental results demonstrate a 63.3% reduction in root-mean-squared error over the existing calibration method. VC 2011 Society for Imaging Science and Technology. [DOI: 10.2352/J.ImagingSci.Technol.2011.55.6.060505] INTRODUCTION The color reproduction quality of an electrophotographic (EP) printing system can be affected by changes in operating conditions. A tone reproduction curve (TRC) is commonly used to characterize the color that is reproduced on the printed media for each primary color. A TRC is obtained by measuring the reproduced color on the output media at a set of predetermined halftone levels. A consistent TRC implies that the reproduced color does not change under different operating conditions. Ensuring the consistency of the TRCs is the first step to ensure consistent color reproduction. Calibrations are performed in an EP system to improve TRC consistency. For an EP engine, tone reproduction on a given media is sensitive to variations in temperature, humidity, air pressure, organic photoconductor (OPC) drum age, throughputs, and other environmental factors and operating conditions. During a calibration, a number of primary color patches are printed on either the internal transfer media or the final output media at a set of predetermined halftone levels. Sensors embedded in the printer measure the printed patches. EP control parameters and the tone correction mapping are adjusted based on these on-board sensor measurements to ensure consistent primary color reproduction. Researchers have proposed approaches to improve tone reproduction consistency. Li and Dianat proposed a calibration routine to minimize least-squared photoconductor TRC errors under various operating conditions using a static linear model between the EP parameters and the sensor values with the presence of disturbances and uncertainty in the system description. Staelin et al. developed machine learning models to improve color reproduction consistency for an HP Indigo digital press. Sim et al. used time-sequential sampling to address the difficulty in generating reliable measurements that span the color gamut of a color EP engine. Totsuka et al. proposed a tone curve Received Sep. 27, 2010; accepted for publication Aug. 8, 2011; published online Dec. 16, 2011 1062-3701/2011/55(6)/060505/9/$20.00. J. Imaging Sci. Technol. Nov./Dec. 2011 060505-1 Journal of Imaging Science and TechnologyV 55(6): 060505-1–060505-9, 2011. VC Society for Imaging Science and Technology 2011

70.2: Virtual Display: A Platform for Evaluating Display Color Calibration Kits

AbstractWe propose a method of evaluating the performance of color calibration kits for LCD monitors. Routine color calibration is imperative for critical applications that rely on color fidelity such as digital pathology and professional graphics. However, the commercially available products vary greatly in price and performance with no available evaluation standard. We propose the concept of Virtual Display, a universal display platform that emulates tone reproduction curves. A field programmable gate array board was used to process the video signals based on a preprogrammed look‐up table, which contains the tone reproduction curves of the target display. A spectroradiometer‐based and a colorimeter‐based color calibration kits were challenged by 8 virtual displays that have problematic tone reproduction curves. The results show that both color calibration kits offer only one‐dimensional lookup tables for each channel, which might be insufficient. We also spectrally characterized three real displays of different grades and derived spectral models for them. By using the virtual display and spectral models, evaluation of color calibration kits can be greatly simplified and standardized without the burden of optical measurement on target displays.

How to Control the Tone Reproduction Curves in Color Separation Works

How to Control the Tone Reproduction Curves in Color Separation Works

P‐86: Channel‐Dependent GOG Model for Colorimetric Characterization of LCDs

AbstractAccurate colorimetric characterization is an important step in establishing the color management system (CMS) for liquid crystal displays (LCDs) to achieve device‐independent color reproduction. The gain‐offset‐gamma (GOG) model that is accurate enough in describing the tone reproduction curves (TRCs) for CRT displays has been found inadequate for characterizing LCDs due to mainly channel interaction and non‐constancy of channel chromaticity. In this paper, a modified GOG model that takes channel interaction and backlight leakage into account is proposed to accurately characterize the TRCs of LCDs. Experimental results indicate that the proposed model outperforms the conventional GOG model in terms of the CIEDE2000 color difference between the XYZ values of the measured color sample and the estimated XYZ values.

A Visual Calibration Method for Calibrating the Tone Reproduction Curve and the Chromaticity of White Point of a Monitor

A Visual Calibration Method for Calibrating the Tone Reproduction Curve and the Chromaticity of White Point of a Monitor

Visual gamma measurement and methods to compare gamma models

Abstract— The correct estimation of the gamma exponent describing the tone‐reproduction curve of a display is an important step in color management. Several methods for visual gamma estimation have been proposed. In this study, the theoretical merits and practical problems of a number of these methods are discussed and compared, and improvements are suggested. A new method to compare gamma models with different numbers of parameters is introduced. In an experiment, spatial and temporal brightness‐matching methods were tested with 32 untrained subjects working on a CRT and an LCD with different resolutions under office and low‐illumination conditions. Illumination had no effect on gamma estimations. Subjects had great difficulties with spatial brightness matching at low resolutions. Temporal and spatial visual brightness matching for untrained subjects showed a larger gamma than photometric fits.

Rank-ordered error diffusion: method and applications

We present a specialized form of error diffusion (ED) that addresses certain long-standing problems associated with operating on images possessing halftone structure and other local high-contrast structures. For instance, image-quality defects often occur when rendering a scanned halftone image to printable form via quantization reduction. Rendering the scanned halftone via conventional ED produces fragmented dots, which can appear grainy and be unstable in printed density. Rendering by thresholding or rehalftoning often produces moiré, and descreening blurs the image. Another difficulty arises in printers that utilize a binary image path, where an image is rasterized directly to halftone form. In that form it is difficult to perform basic image processing operations such as applying a digital tone reproduction curve. Rank-order error diffusion (ROED) has been developed to address these problems. ROED utilizes brightness ranking of pixels within a diffusion mask to diffuse quantization error at a pixel. This approach results in an image-structure-adaptive quantization with useful properties. We describe the basic methodology of ROED as well as several applications in processing halftone images.

Accurate display gamma functions based on human observation

AbstractThis article describes an accurate method to obtain the tone reproduction curve of display devices without using a measurement device. It is an improvement of an existing technique based on human observation, solving its problem of numerical instability and resulting in functions in log—log scale which correspond better to the nature of display devices. We demonstrate the efficiency of our technique on different monitor technologies, comparing it with direct measurements using a spectrophotometer. © 2007 Wiley Periodicals, Inc. Col Res Appl, 32, 310–319, 2007

Improved Calibration of Optical Characteristics of Paper by an Adapted Paper-MTF Model

The calibration of color printers is highly influenced by optical scattering. Light scattered at microscopic level within printed papers induces a blurring phenomenon that affects the linearity of the tone reproduction curve. The induced nonlinearity is known as optical dotgain. Engeldrum and Pridham analyzed its impact on printing, using Oittinen's light scattering model. They determined the scattering and absorption coefficients based on spectral measurements of solid patches only. Their calibration achieves good independence of any printing irregularities. However, the microscopic knife-edge measurements of Arney et al. showed that the model overestimates the influence of the absorption coefficient. Unlike Oittinen's model, we directly approach the laterally scattered light fluxes. This is achieved by an extended three-dimensional Kubelka-Munk model. We describe how to determine our coefficients using measurements of mere solid patches, which allows us to decouple the optical dot gain from other printing influences. Our improved model successfully corrects the observed overestimation and is able to predict Arney's microscopic measurements.

A Tone Reproduction of Displayed and Printed Images Predicted by Using CIECAM02

It is known that preferred tone reproduction is affected by color appearance phenomena. Therefore a preferred tone reproduction curve can be obtained if using a color appearance model that can predict color appearance phenomena accurately. Many color appearance models have been proposed, and the latest color appearance model is CIECAM02 that CIE published in 2004. The CIECAM02 model takes into account Stevens effect, but CIECAM97s, the base model of CIECAM02, does not deal with high levels of illumination such as sunlit conditions. Then, we examined whether the CIECAM02 model could give a tone reproduction curve similar to the preferred tone reproduction curve of conventional photography or not. As a result, it was found that the CIECAM02 model could not be used to predict preferred tone reproduction curves. In addition, we measured tone reproduction curves of two typical imaging systems, DSCs (Digital Still Cameras) and displays, and DSCs and printers. Comparison of the obtained curves with those from the CIECAM02 model showed that they considerably differed in shape.