Search Results (35)

Several minerals are known to undergo chromatic variations when exposed to sunlight, particularly ultraviolet (UV) radiation. These phases, defined as photosensitive, exhibit colour change due to photochemical reactions. To understand this phenomenon, this study investigates the colour alteration in 26 common mineral phases, aiming to better understand their behaviour under artificial ageing conditions. Each mineral was firstly chemically characterised by SEM-EDS to identify common chromophoric impurities. Subsequently, samples were exposed to UV radiation in the climatic chamber. The colour shifts were semi-quantitatively assessed in the CIEL*a*b* colour space after ageing. The results indicate that just 4 minerals out of 26 display negligible colour variation, whereas 22 show evident colour changes. These findings highlight the vulnerability of photosensitive minerals to UV-induced colour changes and raise concerns regarding their behaviour in artworks, historical surfaces, and cultural heritage objects. As such minerals are frequently found in the heritage field, understanding their photochemical responses is essential for developing informed preventive conservation strategies, particularly concerning light exposure in both museum and outdoor contexts. Full article

Background: The present study investigated the relation between dental inclination, colorimetric variation, and aesthetic perception according to the modification of incisor inclination. Smile aesthetics, shaped by morphological factors and patient perception, are vital for social attractiveness and treatment success. This study aimed to assess the effect of varying head tilt on the perceived colour of upper central incisors by simulating changes in torque of the tooth, as well as evaluate factors influencing the perception of an aesthetic smile, including morphological characteristics and gingival aesthetic parameters. Methods: The study was comprised of three stages: colour analysis, evaluation of micro- and mini-aesthetic smile features, and an image-based assessment to determine evaluator perceptions and overall smile attractiveness. A sample of 50 students with complete, lesion-free anterior dentition was analysed. To simulate the effect of orthodontic torque changes during colour analysis, subjects tilted their heads downward and upward, representing palatal and buccal crown torque, respectively. Standardized macro-intraoral photographs were captured under controlled lighting conditions using a DSLR camera stabilized on a tripod in the different positions: the neutral head position (p0), 15° upward (p + 15), and 15° downward (p − 15). Digital colour analysis was conducted in the CIELAB colour space (L*, a*, b*). In the next stage, focusing on micro- and mini-aesthetic evaluation, an additional 50 smiles were generated using artificial intelligence via the SmileCloud program—one digitally enhanced smile per subject—complementing the initial set of 50 spontaneous smiles. These 100 smile images were evaluated by 50 laypersons and 50 dentists using a visual analogue scale via an online questionnaire, in order to assess perceptions, determine smile attractiveness, and quantify gingival aesthetic parameters. Results: The statistically significant regression results are as follows: those for the L* values in all three head inclinations: downward (−15 degrees), upward (+15 degrees), and total tilting (−15 to +15 degrees), as well as for the a* values for downward tilting and the b* values for total tilting. When the head is tilted downwards, the central incisors are positioned retrusively, and the L* b* values reveal a darker and more yellowish appearance, whereas, with the head tilted upwards, the central incisors protrude, and L* a* values indicate a brighter and more greenish appear. In the evaluation stage of the smile aesthetics study, no significant differences were observed in the judgments between laypersons and dentists or between males and females. Smiles with a high or average anterior line, parallel arc, upward lip curvature, visible first/second premolars, a smile index of 5.08–5.87, and symmetry score of 1.04 were rated as more attractive. Significant asymmetries were observed between upper dental hemi-quadrants in gingival contour and interdental papilla height, highlighting subtle morphological variations relevant to smile aesthetics. Conclusions: Aesthetic assessment revealed that the findings suggest a measurable impact of head position on dental colour perception and aesthetic evaluation. Evaluator variables including profession and gender exerted negligible effects on aesthetic perception, whereas smile attractiveness features and gingival aesthetic parameters demonstrate significant clinical applicability in patient management. Full article

Monitoring pH and acidity during yoghurt fermentation is essential for product quality and process efficiency. Conventional measurement methods, however, are invasive and labour-intensive. This study developed artificial neural network (ANN) models to predict pH and titratable acidity during yoghurt fermentation using CIELAB colour parameters (L, a*, b*). Reconstituted milk powder with 12% total solids was prepared with varying protein levels (4.2–4.8%), inoculum concentrations (1–3%), and fermentation temperatures (36–44 °C). Data were collected every 10 min until pH 4.6 was reached. Forty models were trained for each output variable, using 90% of the data for training and 10% for validation. The first two phases of the fermentation process were clearly distinguishable, lasting between 4.5 and 7 h and exceeding 0.6% lactic acid in all treatments evaluated. The best pH model used two hidden layers with 28 neurons (R² = 0.969; RMSE = 0.007), while the optimal acidity model had four hidden layers with 32 neurons (R² = 0.868; RMSE = 0.002). The strong correlation between colour and physicochemical changes confirms the feasibility of this non-destructive approach. Integrating ANN models and colourimetry offers a practical solution for real-time monitoring, helping improve process control in industrial yoghurt production. Full article

Peripheral circulatory failure refers to a condition in which the blood flow through superficial capillaries is markedly reduced or completely occluded. In clinical practice, nurses strictly adhere to regular repositioning protocols to prevent peripheral circulatory failure, during which the skin condition is evaluated visually. In this study, skin colour changes resulting from pressure application were continuously captured using a camera, and supervised machine learning was employed to classify the data into two categories: before and after pressure. The evaluation of practical colour space components revealed that the h component of the JCh colour space demonstrated the highest discriminative performance (Area Under the Curve (AUC) = 0.88), followed by the a* component of the CIELAB colour space (AUC = 0.84) and the H component of the HSV colour space (AUC = 0.83). These findings demonstrate that it is feasible to quantitatively evaluate skin colour changes associated with pressure, suggesting that this approach can serve as a valuable indicator for dimensionality reduction in feature extraction for machine learning and is potentially an effective method for preventing pressure-induced skin injuries. Full article

Recently, the development of nanoparticle pigments has attracted interest in chemical preparation due to their potential functional properties, such as phosphate-based pigments. The present research focuses on the feasibility of synthesising the BaCr₂(P₂O₇)₂ pigment under hydrothermal conditions. The effect of the microstructural features of ceramic pigments (the crystalline structure, morphology, and particle size) on their optical properties (colour and reflectance) was also studied. The BaCr₂(P₂O₇)₂ compound was prepared in different fluid media, including water and NaOH solutions (0.5–1.0 M), at several reaction temperatures (170–240 °C) and intervals (6–48 h). The single-phase BaCr₂(P₂O₇)₂ did not crystallise without by-products (BaCr₂O₁₀, BaCr₂(PO₇)₂) in water and the alkaline solutions, even at 240 °C for 48 h; in these fluids, the ionic Cr³⁺ species oxidised to Cr⁶⁺. In contrast, the BaCr₂(P₂O₇)₂ single-phase crystallisation was favoured by adding urea as a reductant agent (25.0–300.0 mmol). Monodispersed BaCr₂(P₂O₇)₂ fine particles with a mean size of 44.0 nm were synthesised at a low temperature of 170 °C for 6 h with 0.5 M NaOH solution in the presence of 50.0 mmol urea. The phosphate pigment particle grew to approximately 62.0 nm by increasing the treatment temperature to 240 °C. A secondary dissolution–recrystallisation achieved after 24 h triggered a change in the particle morphology coupled with the incrementation of the concentration of NaOH in the solution. The pyrophosphate BaCr₂(P₂O₇)₂ pigments prepared in this study belong to the green colour spectral space according to the CIELab coordinates measurement, and exhibit 67.5% high near-infrared (NIR) solar reflectance. Full article

The image analysis of plants provides an opportunity to measure changes in growth and physiology quantitatively, and non-destructively, over time providing significant advantages over traditional methods of assessment which often rely on qualitative and subjective measures to distinguish between different treatments or genotypes in an experiment. Image analysis techniques are commonly deployed for the analysis of plants in the field or glasshouse, but few studies have demonstrated the use of image analysis to phenotype plants grown under aseptic conditions in culture media. Lolium × hybridum Hausskn ‘Shogun’ plants were germinated in vitro and cultured on media containing combinations of thidiazuron [1-phenyl-3-(1,2,3-thiadiazol-5-yl) urea] (TDZ), N6-benzylaminopurine (BA) and gibberellic acid (GA3) or on phytohormone-free control media. RGB images were taken of the plants throughout the experiment and morphological image analysis techniques were used to quantify changes in plant development. A novel approach to quantitatively measure ’greenness‘ in plants using the CIELAB colour model (L*a*b) colour space from RGB images was developed. This methodology could be utilised to develop improved in vitro growth protocols for Lolium and grass species with similar morphology. Full article

In this paper, we introduce Pixelator v2, a novel perceptual image comparison method designed to enhance security and analysis through improved image difference detection. Unlike traditional metrics such as MSE, Q, and SSIM, which often fail to capture subtle but critical changes in images, Pixelator v2 integrates the LAB (CIE-LAB) colour space for perceptual relevance and Sobel edge detection for structural integrity. By combining these techniques, Pixelator v2 offers a more robust and nuanced approach to identifying variations in images, even in cases of minor modifications. The LAB colour space ensures that the method aligns with human visual perception, making it particularly effective at detecting differences that are less visible in RGB space. Sobel edge detection, on the other hand, emphasises structural changes, allowing Pixelator v2 to focus on the most significant areas of an image. This combination makes Pixelator v2 ideal for applications in security, where image comparison plays a vital role in tasks like tamper detection, authentication, and analysis. We evaluate Pixelator v2 against other popular methods, demonstrating its superior performance in detecting both perceptual and structural differences. Our results indicate that Pixelator v2 not only provides more accurate image comparisons but also enhances security by making it more difficult for subtle alterations to go unnoticed. This paper contributes to the growing field of image-based security systems by offering a perceptually-driven, computationally efficient method for image comparison that can be readily applied in information system security. Full article

Anti-hail nets have been employed in viticulture to reduce the damage caused by hailstorms, but whether this strategy may have detrimental effects on grape quality in the Mediterranean region is still unknown. This study was carried out in the Salento region during the 2023 harvest to evaluate the grape microclimate and fruit quality attributes of ‘Fiano’ white grapes grown uncovered or covered with either crystal or black nets. The nets had a small but significant effect on the air temperature (about 0.3 °C and 0.1 °C higher with black and crystal nets, respectively) and relative humidity (about 1% lower with both black and crystal nets) in the grape zone. However, no significant variation was recorded for grape colouration (except for the chromaticity coordinate a*) nor for the main skin photosynthetic pigments (chlorophyll a, chlorophyll b, carotenoids), the total polyphenolic content, and the total soluble solids. Our preliminary results suggest that anti-hail nets can be effective to protect the grapevines against hailstorms and other adverse weather conditions, without having negative impacts on the colour development and bioactive compounds of white grapes in the Mediterranean region. Full article

The pursuit of aesthetic excellence in dentistry, shaped by societal trends and digital advancements, highlights the critical role of precise shade matching in restorative procedures. Although conventional methods are prevalent, challenges such as shade guide variability and subjective interpretation necessitate a re-evaluation in the face of emerging non-proximity digital instruments. This systematic review employs PRISMA protocols and keyword-based search strategies spanning the Scopus^®, PubMed.gov, and Web of Science^TM databases, with the last updated search carried out in October 2023. The study aimed to synthesise literature that identified digital non-proximity recording instruments and associated colour spaces in dentistry and compare the clinical outcomes of digital systems with spectrophotometers and conventional visual methods. Utilising predefined criteria and resolving disagreements between two reviewers through Cohen’s kappa calculator, the review assessed 85 articles, with 33 included in a PICO model for clinical comparisons. The results reveal that 42% of studies employed the CIELAB colour space. Despite the challenges in study quality, non-proximity digital instruments demonstrated more consistent clinical outcomes than visual methods, akin to spectrophotometers, emphasising their efficacy in controlled conditions. The review underscores the evolving landscape of dental shade matching, recognising technological advancements and advocating for methodological rigor in dental research. Full article

No gingival shade guide exists that can be used as a ‘gold standard’ in gingival shade selection. This research, therefore, aimed to determine whether comparable results in subjective gingival shade selection can be achieved using basic gingival colours produced by distinct manufacturers. It also aimed to explore how coverage of the colour space is affected by mixing these basic colours to create additional shades. To achieve these objectives, the basic gingival colours of three ceramic systems (Heraceram, Kulzer, Madrid, Spain; Vita VM9, Vita Zahnfabrik, Bad Säckingen, Germany; IPS Style, Ivoclar, Schaan, Liechtenstein) were analysed. The colour systems were expanded by creating porcelain gingival samples, whose colours were obtained by mixing the basic colours, altering each mixture by increments of 10%, and respecting the numerical order used by manufacturers to identify the colours. The colour coordinates of the basic and additional colours were recorded using spectrophotometry, and the intra- and inter-system colour differences were calculated using the Euclidean (ΔE_ab) and CIEDE2000 (ΔE₀₀) formulae. None of the basic colours in the three systems, despite their similar nomenclature, were found to be interchangeable (the colour differences exceeded the gingival acceptability threshold: ΔE₀₀ 2.9 units). The expanded gingival colour systems, with mixtures altered by 10% increments, notably increased the gingival colour space covered by the original systems. The authors concluded that there are clear differences between the basic gingival colours produced by distinct manufacturers using the same nomenclature. Ceramic samples produced by mixing basic gingival colours are a resource with the potential to improve subjective gingival shade matching. Full article

Monascus purpureus is a red pigment-producing fungus. In the present study, the effect of fish hydrolysate and sodium chloride on the colour of quinoa flour fermented with M. purpureus was analysed. The colour of each sample was evaluated in CIELAB space (L*, a*, b*), in addition to the C:N ratio. The minimum fermentation time was eight days and the values of L* (44.66 ± 0.532), a* (20.27 ± 0.323), b*(17.89 ± 1.342) and a C:N ratio of 11.05 ± 0.240 were obtained. Therefore, there is an effect of supplementation on increasing the red colour of the meal. This work opened up the possibility that red quinoa flour could be used as a raw material in the production of other food products. Full article

Navigation line extraction is critical for precision agriculture and automatic navigation. A novel method for extracting navigation lines based on machine vision is proposed herein using a straight line detected based on a high-ridge crop row. Aiming at the low-level automation of machines in field environments of a high-ridge cultivation mode for broad-leaved plants, a navigation line extraction method suitable for multiple periods and with high timeliness is designed. The method comprises four sequentially linked phases: image segmentation, feature point extraction, navigation line calculation, and dynamic segmentation horizontal strip number feedback. The a* component of the CIE-Lab colour space is extracted to preliminarily extract the crop row features. The OTSU algorithm is combined with morphological processing to completely separate the crop rows and backgrounds. The crop row feature points are extracted using an improved isometric segmented vertical projection method. While calculating the navigation lines, an adaptive clustering method is used to cluster the adjacent feature points. A dynamic segmentation point clustering method is used to determine the final clustering feature point sets, and the feature point sets are optimised using lateral distance and point line distance methods. In the optimisation process, a linear regression method based on the Huber loss function is used to fit the optimised feature point set to obtain the crop row centreline, and the navigation line is calculated according to the two crop lines. Finally, before entering the next frame processing process, a feedback mechanism to calculate a number of horizontal strips for the next frame is introduced to improve the ability of the algorithm to adapt to multiple periods. The experimental results show that the proposed method can meet the efficiency requirements for visual navigation. The average time for the image processing of four samples is 38.53 ms. Compared with the least squares method, the proposed method can adapt to a longer growth period of crops. Full article

The new Construction 4.0 paradigm takes advantage of existing technologies. In this scope, the development and application of image-based methods for evaluating and monitoring the state of conservation of buildings has shown significant growth, including support for maintenance plans. Recently, powerful algorithms have been applied to automatically evaluate the state of conservation of buildings using deep learning frameworks, which are utilised as a black-box approach. The large amount of data required for training, the difficulty in generalising, and the lack of parameters to assess the quality of the results often make it difficult for non-experts to evaluate them. For several applications and scenarios, simple and more intuitive image-based approaches can be applied to support building inspections. This paper presents the StainView, which is a fast and reliable method. The method is based on the classification of the mosaic image, computed from a systematic acquisition, and allows one to (i) map stains in facades; (ii) locate critical areas; (iii) identify materials; (iv) characterise colours; and (v) produce detailed and comprehensive maps of results. The method was validated in three identical buildings in Bairro de Alvalade, in Lisbon, Portugal, that present different levels of degradation. The comparison with visual inspection demonstrates that StainView enables the automatic location and mapping of critical areas with high efficiency, proving to be a useful tool for building inspection: differences were of approximately 5% for the facade with the worst and average state of conservation, however, the values deteriorate for the facade under good conditions, reaching the double of percentage. In terms of processing speed, StainView allows a facade mapping that is 8–12 times faster, and this difference tends to grow with the number of evaluated façades. Full article

Enhancing underwater images presents a challenging problem owing to the influence of ocean currents, the refraction, absorption and scattering of light by suspended particles, and the weak illumination intensity. Recently, different methods have relied on the underwater image formation model and deep learning techniques to restore underwater images. However, they tend to degrade the underwater images, interfere with background clutter and miss the boundary details of blue regions. An improved image fusion and enhancement algorithm based on a prior dark channel is proposed in this paper based on graph theory. Image edge feature sharpening, and dark detail enhancement by homomorphism filtering in CIELab colour space are realized. In the RGB colour space, the multi-scale retinal with colour restoration (MSRCR) algorithm is used to improve colour deviation and enhance colour saturation. The contrast-limited adaptive histogram equalization (CLAHE) algorithm defogs and enhances image contrast. Finally, according to the dark channel images of the three processing results, the final enhanced image is obtained by the linear fusion of multiple images and channels. Experimental results demonstrate the effectiveness and practicality of the proposed method on various data sets. Full article

To quantify the discolouration of the temporary acetal resins in vivo, based on the weeks of follow-up and the salivary pH in the three thirds of the tooth. To find out if the final CIELAB coordinates can be predicted from the initial colour coordinates, the salivary pH, the situation (in thirds) and the weeks of follow-up. Colour coordinates (L, C, and h) were recorded by spectrophotometry in 13 participants fitted with hybrid provisional complete dentures made of acetal resin. Colour recordings were made on the day of placement and after several weeks of follow-up (6 to 31 weeks). Salivary pH was also measured as a predictor variable for colour change. The ANOVA statistical test and regression models have been used. The highest colour difference according to ∆Eab* was 27.46 units after 15 weeks of follow-up and the lowest was 7.34 units after 17 weeks of follow-up. Neither in the cervical nor in the middle third any regressor variable (initial L*, initial C*, initial h*, salivary pH and weeks of follow-up) was able to significantly predict any of the final colour coordinates (p > 0.05). The colour change of the temporary acetal resins used exceeds the threshold of clinical acceptability, and it is not acceptable to maintain satisfactory aesthetics. The weeks of follow-up and the salivary pH are not capable of satisfactorily predicting the final color coordinates of the acetal resins. Full article