Digital Color Reproduction Research Articles

Study on Influence Factor Analysis and Optimal Methodology for Color Reproduction of Digital Photography of Painted Cultural Heritage

The color management system (CMS) for digital photographs of painted cultural heritage requires consideration of the camera as an input device, lighting as a shooting condition, and color charts and spectrophotometers as absolute color standards. Therefore, this study conducted basic experiments to derive the effects of these factors on digital color reproduction and the application methodology. The results showed that the two types of spectrophotometers for CMS and the spectrophotometer used for direct measurement of painted cultural heritage showed almost similar color reproduction, and the digital camera did not have a significant effect on color reproduction regardless of the operating principle, image sensor type, and resolution. Although the color reproduction under the three lighting conditions was execellent overall, the instantaneous and continuous light used in the experiment showed a lower color difference than the LED light. When these optimal conditions were applied to the Dancheong (traditional multicolored paintwork) specimen, the color difference of <i>Δ</i>11.57 before color reproduction decreased dramatically to <i>Δ</i>1.02 after color reproduction. This means that the digital color reproduction process brought the Dancheong specimen has become closer to the true color. Digital photography is an essential recording method in the process of conserving and utilizing cultural heritage. In the absence of manuals or guidelines for digital photography-based color reproduction, basic experimental research has great potential as a methodology for the documentation of painted cultural heritage. In addition, if color reproduction technology is applied to three-dimensional scanning, where the importance of color recording is relatively overlooked, it is believed that the digital recording process can be advanced and actively used for the conservation of painted cultural heritage.

Effect of Polarization on RGB Imaging and Color Accuracy/Fidelity

The use of polarization while trying to keep the digital color reproduction accuracy at its finest is very challenging due to how polarization is interacting and affecting the light spectrum itself and due to the quality of the used polarization materials. Our study on RGB imaging and color reproduction’s fidelity with and without polarization shows that a cross circular polarization (on a camera lens and light source) will have a major impact on how a linear grayscale, whether it has a semi-glossy or matt finishing, would be reproduced in contrast to no polarization at all. A major loss in deep black shades in the case of a semi-glossy grayscale is unmistakable. In addition to a noticeable shift in both lightness and Chroma components regardless of the grayscale’s finishing but depending rather on the used color target for correction. DE00 could not paint the full picture about color fidelity despite its low conformant reported values. Whereas, a closer visual inspection of the color components separately (lightness and Chroma) reveals color reproduction problems caused by polarization.

A Study on Digital Color Reproduction for Recording Color Appearance of Cultural Heritage

The color appearance of cultural heritage are essential factors for manufacturing technique interpretation, conservation treatment usage, and condition monitoring. Therefore, this study systematically established color reproduction procedures based on the digital color management system for the portrait of Gwon Eungsu. Moreover, various application strategies for recording and conserving the cultural heritage were proposed. Overall color reproduction processes were conducted in the following order: photography condition setting, standard color measurements, digital photography, color correction, and color space creation. Therefore, compared with the color appearance, the digital image applied to a camera maker profile indicated an average color difference of Δ10.1. However, the digital reproduction result based on the color management system exhibits an average color difference of Δ1.1, which is close to the color appearance. This means that although digital photography conditions are optimized, recording the color appearance is difficult when relying on the correction algorithm developed by the camera maker. Therefore, the digital color reproduction of cultural heritage is required through color correction and color space creation based on the raw digital image, which is a crucial process for documenting the color appearance. Additionally, the recording of color appearance through digital color reproduction is important for condition evaluation, conservation treatment, and restoration of cultural heritage. Furthermore, standard data of imaging analysis are available for discoloration monitoring.

DIGITAL COLOR REPRODUCTION AND DOCUMENTATION OF OIL PAINTING USING IMAGE PROCESSING

Abstract. Digital photography is a method easily employed to capture images. Mobile devices such as smartphones and tablets as well as dedicated cameras are used to capture images. Furthermore, as hardware continues to improve, the resolution of images in 100 MP and 8K videos has recently been increased, and the quality of images enhanced through various types of image processing software. However, because the focus of photography is to record a moment activity, recording the orginal color of subject has been pushed back from priority. Digital photographs of cultural heritage are mainly captured for aesthetic appreciation and database construction. Those images for the purpose of the latter should record the exact color and shape of the subject. However, the theoretical approach of this is difficult and relatively complex procedures are able to create images that differ from the original color. Thus, it means falling in value that culture heritage data of important for color conservation. Various attempts have been made throughout the industry to capture the original colors of the subject accurately. The color management system (CMS) is a typical method of such. In this study, digital color reproduction and record studies were conducted on representative oil paintings of modern times in Korea. Accordingly, the light source’s color index and color temperature were measured. Furthermore, a color recording environment was established and digital images were acquired. Subsequently, it was able to record the original color through CMS-based image processing. It is believed that this study will enable one to understand the production techniques of works through the color record of oil paintings and help one to monitor conservation conditions such as discoloration.

The limits of colorimetry in cultural heritage applications

AbstractColours in cultural heritage are not only means of expression, but also materials with physical and chemical properties. Since the beginning of the current century, colorimetry has become a fundamental field aiming at restoring, preserving and valorising the art works. There are different colorimetric applications in cultural heritage (eg, from light design to digitisation and modelling), and the variety of cultural material is extremely wide, from statues and frescoes, to old book and films. In this heterogeneous context, the development of instruments, measurements and tools faithful to the original objects are fundamental to correctly reproducing and representing materials, contrast and colours of the works under analysis. In this work, we will analyse the main limits of colorimetry applied in cultural heritage domain considering a variety of applications on physical colour representation and on digital colour reproduction. We will focus on main state‐of‐the‐art studies, regulations and guidelines for objects illumination, colour analysis and digitisation workflow showing some practical example of issues encountered by standard pointwise colorimetry.

Skin colour assessment of replanted fingers in digital images and its reliability for the incorporation of images in nursing progress notes.

To determine whether nurses can accurately assess the skin colour of replanted fingers displayed as digital images on a computer screen. Colour measurement and clinical diagnostic methods for medical digital images have been studied, but reproducing skin colour on a computer screen remains difficult. The inter-rater reliability of skin colour assessment scores was evaluated. In May 2014, 21 nurses who worked on a trauma ward in Japan participated in testing. Six digital images with different skin colours were used. Colours were scored from both digital images and direct patient's observation. The score from a digital image was defined as the test score, and its difference from the direct assessment score as the difference score. Intraclass correlation coefficients were calculated. Nurses' opinions were classified and summarised. The intraclass correlation coefficients for the test scores were fair. Although the intraclass correlation coefficients for the difference scores were poor, they improved to good when three images that might have contributed to poor reliability were excluded. Most nurses stated that it is difficult to assess skin colour in digital images; they did not think it could be a substitute for direct visual assessment. However, most nurses were in favour of including images in nursing progress notes. Although the inter-rater reliability was fairly high, the reliability of colour reproduction in digital images as indicated by the difference scores was poor. Nevertheless, nurses expect the incorporation of digital images in nursing progress notes to be useful. This gap between the reliability of digital colour reproduction and nurses' expectations towards it must be addressed. High inter-rater reliability for digital images in nursing progress notes was not observed. Assessments of future improvements in colour reproduction technologies are required. Further digitisation and visualisation of nursing records might pose challenges.

Neural network approach to a colorimetric value transform based on a large‐scale spectral dataset

To improve the transform accuracy of colorimetric values for digital colour reproduction, a neural network approach based on a large-scale spectral dataset was proposed. The presented dataset exhibited a particularly wide colour gamut and was partitioned into 12 subsets according to dominant wavelength and excitation purity. In each subset, the non-linearity between colorimetric values under source and target illuminant–observer combinations was simulated by a backpropagation neural network. The colorimetric transform accuracy of this approach was compared with several existing methods. The experimental results indicated that the proposed approach significantly enhanced the transform precision for colorimetric values, especially for the colours located in highly saturated regions.

Reducing Inkjet Ink Consumption with RIP software for POP Display Media

Most media used for POP display are not paper-based substrates. Finding an appropriate digital print configuration becomes crucial for color reproduction of display media. In most situations, running a digital printer wide-open without ink restriction will not achieve the most accurate, repeatable color. A third-party raster imaging processor (RIP) software interprets raster and vector data files for a specific postscript printer in either RGB or CMYK mode. By controlling CMYK inks directly, RIP software can provide better control for accurate digital color reproduction while reducing ink consumption. The purpose of this project is to reduce ink usage while achieve accurate/repeatable digital color reproduction for display media by establishing a digital print configuration with RIP software for tested display media. Four commercially available display media (DuPont Tyvek, Polypropylene, Satin Cloth, and Vinyl) were used in this study. A third-party RIP software, CGS ORIS Color Tuner, was used to control an Epson Stylus Pro 4800 inkjet printer. The ink usage was determined in terms of amount of ink restriction. Color reproduction quality was evaluated in terms of color gamut volume and inkjet-hooking diagram.

Visual gamma correction for LCD displays

An improved method for visual gamma correction is developed for LCD displays to increase the accuracy of digital colour reproduction. Rather than utilising a photometric measurement device, we use observers’ visual luminance judgements for gamma correction. Eight half tone patterns were designed to generate relative luminances from 1/9 to 8/9 for each colour channel. A psychophysical experiment was conducted on an LCD display to find the digital signals corresponding to each relative luminance by visually matching the half-tone background to a uniform colour patch. Both inter- and intra-observer variability for the eight luminance matches in each channel were assessed and the luminance matches proved to be consistent across observers (Δ E 00 < 3.5) and repeatable (Δ E 00 < 2.2). Based on the individual observer judgements, the display opto-electronic transfer function (OETF) was estimated by using either a 3rd order polynomial regression or linear interpolation for each colour channel. The performance of the proposed method is evaluated by predicting the CIE tristimulus values of a set of coloured patches (using the observer-based OETFs) and comparing them to the expected CIE tristimulus values (using the OETF obtained from spectro-radiometric luminance measurements). The resulting colour differences range from 2 to 4.6 Δ E 00. We conclude that this observer-based method of visual gamma correction is useful to estimate the OETF for LCD displays. Its major advantage is that no particular functional relationship between digital inputs and luminance outputs has to be assumed.

Measurement and Modeling for the Two Dimensional MTF of Human Eye and Its Application for Digital Color Reproduction

Measurement and Modeling for the Two Dimensional MTF of Human Eye and Its Application for Digital Color Reproduction

Precision requirements for digital color reproduction

An environment was established to perform device-independent color reproduction of full-color pictorial images. In order to determine the required precision for this environment, an experiment was performed to psychophysically measure colorimetric tolerances for six images using paired comparison techniques. These images were manipulated using 10 linear and nonlinear functions in the CIELAB dimensions of lightness, chroma, and hue angle. Perceptibility tolerances were determined using probit analysis. From these results, the necessary precision in number of bits per color channel was determined for both the CIELAB and the CRT rgb device color spaces. For both the CIELAB color space and the CRT rgb device space, approximately eight color bits per channel were required for imperceptible color differences for pictorial images, and 10 bits per channel were required for computational precision.

Digital color reproduction on color television monitors

Color displays used in image processing systems consist of a refresh memory buffer storing digital image data which are converted into analog signals to display an image by driving the primary color channels (red, green, and blue) of a color television monitor. The color cathode ray tube (CRT) of the monitor is unable to reproduce colors exactly due to phosphor limitations, exponential luminance response of the tube to the applied signal, and limitations imposed by the digital-to-analog conversion. In this paper we describe some computer simulation studies (using the U * V * W * color space) carried out to measure these reproduction errors. Further, a procedure to correct for color reproduction error due to the exponential luminance response (gamma) of the picture tube is proposed, using a video-lookup-table and a higher resolution digital-to-analog converter. It is found, on the basis of computer simulation studies, that the proposed gamma correction scheme is effective and robust with respect to variations in the assumed value of the gamma.

Digital color reproduction on color television monitors

Digital color reproduction on color television monitors

Digital color reproduction on color television monitors

Digital color reproduction on color television monitors