Rethinking the White Point

This study assessed the relative effects of metameric (preserving illumination chromaticity) vs. chromatic illumination changes on the perceived quality of real fruits. 20 normal trichromats viewed four singly-presented fruits under three neutral metameric illuminations (differing in spectral power distribution with constant CCT of ∼6500K) and two broadband chromatic illuminations (∼2000K and ∼10000K) inside a white-walled lightroom illuminated by spectrally tuneable lamps. Participants’ ratings of nine fruit attributes were used to calculate Positive Attributes Scores (PAS) for each fruit-illumination pair. For two fruits (banana and pear), PAS varied significantly under metameric illumination changes, but not under chromatic illumination changes. PAS varied significantly under both metameric and chromatic illumination changes for orange, and under chromatic illumination changes only for red apple. The findings indicate that metameric illumination changes alter perceived food attributes via changes in fruit colour appearance, while changes in illumination chromaticity may influence perceived food quality independently of fruit colour appearance which is largely maintained via colour constancy.

An end-to-end image reproduction method is proposed to render cultural heritage images under arbitrary illuminating conditions. When displayed on a characterized display, the appearance of paper-based cultural heritages is reproduced as actually observed under the target illumination, by leveraging spectral images of the artworks and spectral power distribution (SPD) of the identical illumination. Psychophysical experiments are conducted to verify that the proposed method outperforms the traditional pipelines on reproducing real scenes, including the CIECAM02 color appearance model. The method has the potential to be applied in the digitization and exhibition of paper cultural heritages.

We have developed an innovative lighting system that changes specific target colors while keeping the lights appearing naturally white. By precisely controlling the spectral power distribution (SPD) of illumination and harnessing the unique phenomenon of metamerism, our system achieves unique color variations in ways you’ve never seen before. Our system calculates the optimal SPDs of illumination for given materials to intensively induce metamerism, and then synthesizes the illumination using various colors of LEDs. We successfully demonstrated the system’s implementation at Paris Fashion Week 2024. As models step onto the stage, their dresses initiate a captivating transformation. Our system altering the colors of the dresses, showcasing an impressive transition from one stunning color to another.

Introduction Patients with neuroproliferative vestibulodynia (NPV), characterized by persistent entry dyspareunia, allodynia, and hyperalgesia, are often treated by complete vestibulectomy with vaginal advancement flap reconstruction. Vestibulectomy surgery involves subepithelial excision of the 1:00– 11:00 and, if appropriate, 12:00 endodermal vestibular regions, with ectodermal vulva anastomosed to mesodermal vagina. NPV patients considering surgery often express concerns pre-operatively regarding post-operative appearance of their genitalia. Counseling for this has been challenging as, to the best of our knowledge, there have been no reported objective assessments of post-operative changes in genital tissue appearance. Objective To objectively assess changes in vulvar genital tissue appearance in NPV patients who underwent complete vestibulectomy. Methods To assess for change in genital tissue appearance post-operatively, we reviewed charts of patients from a single site who i) underwent complete vestibulectomy between September 2022 and February 2024 and ii) returned to the clinic for a post-operative visit including vulvoscopy with photography at least 3 months after surgery. The primary outcome measure was the 8-item modified Vulvar Genital Tissue Appearance (mVGTA) scale. Vulvoscopic photographs were deidentified and blinded as to whether they were from pre-operative or post-operative visits and read by a trained research team member not involved in patient care. Each photograph was graded for appearance using the mVGTA scale. The 8 items assessed individually and as a total were appearance of: labia majora resorption, labia minora resorption, clitoral glans visualization, clitoral adhesions, introitus pallor, introitus erythema, loss of introital moisture, and posterior fourchette tightness; judged on a 0 to 3 ordinal scale (0 = none; 1 = mild; 2 = moderate; 3 = severe). After unblinding, data were analyzed using descriptive statistics and Wilcoxon matched-pairs signed rank tests. In addition, the vaginal advancement flap was examined for both color and scar tissue between the vagina and vulva using the unblinded post operative photographs. Results Eleven patients were included, age 29 years (range 22-35) who met inclusion criteria. The average time from surgery to post-operative vulvoscopy was 6 months (range 3-13). A total of 178 photographs were graded. (Fig. 1) There were statistically significant improvements from pre- to post-operative mVGTA scores for: clitoral glans visualization (p = 0.023), clitoral adhesions (p = 0.0078), introital pallor (p = 0.0078), introital erythema (p = 0.0117), and the total mVGTA score (p = 0.0029).(Figure 2) Of note, 8 patients underwent lysis of clitoral adhesions at the time of vestibulectomy surgery, all with improved scores in clitoral glans visualization and clitoral adhesions. In all 11 patients, the vaginal advancement flap was pink in color and with no scar tissue identified between the vagina and vulva. There were no statistically significant changes in appearance of the labia majora/minora resorption, labial moisture or posterior fourchette tightness (Fig. 2). Conclusions These findings suggest that complete vestibulectomy improves appearance of genital tissue color and clitoral visualization, and does not change the labia majora, labia minora or posterior fourchette tightness. This should reassure patients concerned about genital appearance considering complete vestibulectomy for NPV. Disclosure No.

The work described here forms part of a research project entitled Predictive Perceptual Colour Models. The aim of this project is to develop a colour appearance model capable of predicting changes of colour appearance under various different viewing conditions. This will provide industry with a quantitative measure for assessing the quality of colour reproduction and enable more rapid and accurate proofing simulations in the graphic art industry. A large‐scale experiment has been carried out in which colour appearance was assessed under a wide range of viewing conditions. The parameters studied were (1) D65, D50, white fluorescent, and tungsten light sources, (2) luminance levels of about 40 and 240 cd/m2, (3) five background conditions: white, grey, black, grey with white border, and grey with black border, and (4) two media: luminous colours (displayed on a high‐resolution colour monitor) and nonluminous colours (presented in a viewing cabinet). Each colour was assessed by a panel of six or seven observers using a magnitude estimation method. In total, 43,332 estimations were made, and these form the LUTCHI Colour Appearance Data. Data analysis has been carried out to examine the reliability of the experimental results and to understand the effects of the various viewing parameters studied. (Part II of this article describes how the LUTCHI Colour Appearance Data has been used to test the performance of various colour spaces and models.

In order to meet the ground calibration requirements of Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) satellite gamma ray detector (GRD), two sets of single-energy x-ray calibration devices were established in China Metrology Institute (Changping). One set is a single crystal calibration device, and LiF crystal can realize continuous emission of (8.1-37.9) keV single-energy X-ray; The other set is a dual crystal calibration device. Si220 crystal and Si551 crystal can realize continuous light emission of single energy x-ray in the energy range of (38-160) keV. The X-ray energy spectrum, energy resolution and energy response of the calibration device were studied by standard high-purity germanium detectors. The test results show that the energy range of the calibration device is: (8-160) keV; monochromaticity: energy resolution 3.1%@8.1keV, 10.2%@79.9keV; monochromatic luminous flux 649cts/s@38. 0keV,678cts/s@79.9keV,298cts/s@121.8keV; monochromatic light ratio 96%@38.0keV, 97%@79.9keV, 96%@121.8keV. Combined with the actual test results of the energy point of the GRD, it indicates that the calibration device can meet the calibration requirements of the GRD.

5 - Color Appearance and Color Difference Specification

The spectral sensitivity of the visual system varies markedly between the fovea and surrounding periphery owing in part to the rapid fall in macular pigment density with eccentricity. We examined how colour appearance changes between the fovea and near periphery (88) by measuring achromatic loci and the loci of unique and binary hues. Chosen colours remained much more similar at the two locations than predicted by the change in spectral sensitivity. Compensation for white may reflect long-term gain changes within the cones that equate sensitivity for the local average stimulus in the fovea and periphery. However, adjusting only to the average stimulus cannot correct for all of the effects of a spectral sensitivity change, and predicts differences in colour percepts between the fovea and periphery that were not observed. The similarities in hue percepts at 0 and 88 thus suggest that additional processes help compensate colour appearance to maintain constancy in the near periphery. We model the results of previous studies to show that similar adjustments are implied by age-related changes in lens pigment, and to show that these adjustments are consistent with previous measurements of peripheral colour appearance based on hue cancellation.

The perceived colour of a surface is governed by the spectral reflectance properties of the surface and the spectral power distribution of the illuminating light source. Accurate perception of surface colours is of paramount importance in museums and art galleries. The chromatic characteristics of the light used in exhibition spaces must be carefully chosen, considering the diverse attributes of the exhibits, and it is crucial to maintain the stability of this light colour across time and space. In galleries illuminated by natural daylight, the intensity and colour of light entering through windows vary throughout the day. Moreover, the use of supplementary artificial lighting at different times of the day can amplify changes in the ambient light colour, potentially altering the impact and meaning of artworks and diminishing the artist's intended message. This study investigates the variation in perceived surface colour as a function of the colour of the illuminating light. Red surfaces with varying levels of value and saturation, two spectral power distributions representative of daylight, and nine LED light sources were analysed as lighting conditions. The colour appearances of different surface-light combinations were calculated using the Yxy colour space. To illustrate how the perceived colour of an artwork shifts under different light sources, a geometric graphic design was developed and coloured according to specific colour schemes. The changes in the colours within this graphic, corresponding to varying light sources, were visualized using computer software. The findings emphasize the critical role of light colour in determining the perceived colours of artworks. These results offer valuable insights for the selection of suitable light sources not only for art exhibition spaces but also for other environments featuring colourful objects.

This paper describes physical measures for quantifying the quality of light sources and their characteristics. Typical light sources, including incandescent lamps, fluorescent lamps and light emitting diodes, are first introduced and their performance is compared. The CIE colour specification system is then described, including physical quantities for specifying light sources such as colour temperature, spectral power distribution, luminance, illuminance, luminous efficacy, chromaticity coordinates, uniform colour spaces, a colour difference formula and a colour appearance model. Finally, the CIE colour rendering index, together with recent developments towards a new index, including CRI‐CAM02UCS, is described.

The purpose was to investigate the effects of the spectral power distribution (SPD) and illuminance of task lighting on visual function in age-related macular degeneration (ARMD) compared to normal healthy eyes. Twenty-eight subjects with ARMD and 18 age-matched normal subjects were studied. The effects on visual function were determined for four common task light sources: standard pearl coat incandescent (SP), daylight blue incandescent (DL), warm white fluorescent (WW) and cool white fluorescent (CW). Apart from a small, statistically significant improvement in contrast sensitivity with DL compared to SP lighting (0.5 dB, p = 0.01), there were no significant effects of SPD on other visual functions and no differences in the effects for subjects with ARMD and those with normal vision. Thus, for task lighting typically used in low vision rehabilitation, the SPD would seem to be of minimal clinical importance to visual function. However, increasing the task illuminance had a greater effect on visual function, in particular for subjects with ARMD (p < 0.01). For an increase in illuminance from 300 to 3000 lux, the mean increase in contrast sensitivity and near visual acuity was 1.5 dB and 0.13 log MAR, respectively. Although this effect is not large, we suggest that it is clinically relevant and supports the provision of additional task illuminance as an important part of low vision rehabilitation for patients with ARMD.

We first measured red/green equilibria of a 1o test field superimposed on either a green (540 nm) or red (660 nm) 5°, 32-troland background. The background was then modified by (1) reducing its size to 3° or (2) introducing a dark, thin concentric ring with an outer diameter of 3°. The ring was 12′ wide so, effectively, it changed the 5° background to a 2.6° background surrounded by, but not contiguous with, a 35° (inner-outer diameter) ring. The test was an admixture of 549-and 660-nm light, and was varied from 6 to 300 trolands. The observer adjusted the 549-nm component of the test until the test appeared neither reddish nor greenish. Two color-normal observers participated in the study. Reducing the size of the background from 5° to 3° caused a shift in color appearance at all illuminances of the test. The shift was toward greenness with a 540-nm background and toward redness with a 660-nm background and can be explained by a smaller change in receptoral sensitivity with the smaller background. Introducing a 12′ dark gap in the 5°, 540-nm background had a larger effect than reducing the size from 5° to 3°, implying the influence of the gap is not due simply to less background light. The same gap on a 5°, 660-nm background had an effect opposite the change in color appearance caused by reducing the size of the background: reducing the size from 5° to 3° caused the test to appear more reddish, but adding the dark gap to the 5° background caused the test to appear more greenish. Similar results were found with 320-troland backgrounds. These observations reveal that contours in a background field strongly affect color appearance, and do so in ways qualitatively different from varying the retinal area stimulated by background light. The results point to higher level processes that use edge contrast to differentiate remote from contiguous adapting light.

Rod contributions to color perception: Linear with rod contrast

ANSI/IT8, ANSI/CGATS and ISO/TC130 are actively working on standards that help define color for graphic arts applications. This paper describes the standards already in place as well as a summary of the current status of the work underway and/or planned. This includes standards that define colorimetric measurement, targets and data sets for calibration of input devices such as scanners as well as color hard copy output (including printing) devices and standards for the definition of printing processes. The work to develop characterization data sets for use by color management systems and common data formats for the exchange and presentation of this data are also discussed. Key additional areas include the definition of default three-component color data spaces, their practical encoding in 8- and 16-bit formats, and procedures for definition of ink colors in a printing independent manner.

The experimental data from this study extends the LUTCHI colour‐appearance data to cover transmissive media. Two further experiments were carried out: one used a large cut‐sheet transparency viewed using a back‐lit illuminator, and another used a 35‐mm slide projected onto a white screen. These new data were used to reveal the changes in colour appearance caused by different viewing parameters studied, and to evaluate the predictive accuracy of five uniform colour spaces and colour‐appearance models. The results show that Hunt's 91 model (developed to fit earlier experimental results) did not perform as well as it did in the previous studies using nontransmissive media. This implies that there are large differences in perceived colour appearance between transmissive and nontransmissive media viewing conditions. Some modifications were subsequently made to Hunt's 91 model and the predictive accuracy was greatly improved.