Using Portable Color Sensors to Conduct Densitometric and Colorimetric Measurements in Virtual Classroom Settings

Bethany Wheeler and Shu Chang, Clemson University

Classroom learning and instruction changed drastically over the course of the last year due to the widespread Coronavirus pandemic. In most circumstances, in-person teaching was no longer an option due to the health and safety concerns of students, faculty, staff, and their families. These concerns drove many universities to offer online courses exclusively and launched faculty into virtually delivering course content for the first time. In a discipline such as graphic communications, where hands-on interaction with tools and equipment is one of the main focuses of the curriculum, this sudden shift to online instruction presented a whole new set of challenges. This work aims to identify a portable and affordable color measurement device suitable for the virtual graphic communication curricula and to establish a methodology for performing densitometric and colorimetric measurements in a home environment with online instruction. Using a portable color sensor in the online classroom will allow the students to gather the data and gain conceptual understanding required to succeed in the class. The study is to probe the proficiency for teaching graphic communications concepts.  However, the study is not designed to support any industrial practices.

This paper will present the process of selecting a portable color sensor, the implementation of the sensor in our existing curriculum, and the outcomes. The work has focused on measuring CIE L*a*b* data to examine both color and tone reproductions of prints. The goal has been to illustrate concepts introduced in our curriculum, including color and color difference (ΔE*), tone reproduction, whiteness and opacity, color balance, and even hue error, grayness and overprint trapping. In the existing in-person curriculum, the x-Rite eXact and x-Rite i1io spectrometers have been the standard instruments, but it is not feasible to provide every student with a device to use at home.

Measurement devices sampled in this work are classified as portable color sensors. They are affordable, with a cost similar to textbooks, and easy for students to acquire and use. Past research has assessed the performance of these sensors regarding the success rate of identifying the color of established color chips and has indicated the attractiveness of these sensors for applications that do not require the high accuracy of standard instruments (Kirchner et al., 2019). Typically, the primary users of these devices are graphic designers, photographers, interior designers, paint suppliers, and contractors, etc.

This study hypothesized that one or more portable color sensors would exhibit sufficient accuracy as compared to the x-Rite eXact for colorimetric concept demonstrations. In addition, this exploration converted color values from different tone patches into density to test the consistency to the measurements from the x-Rite eXact.   Prior to introducing new devices into the curriculum, two portable color sensors, Color Muse and Nix Mini 2, were examined. Throughout the early examination process, the CIEL*a*b* values of CMYK inks and RGB overprint patches were collected using the color sensors and their perspective smart phone apps. The values were then converted to CMYK densities, and compared to the values collected with x-Rite eXact devices. The early assessment indicated a superior performance of Nix Mini 2 Color Sensors in comparison to Color Muse in terms of the closeness in values to those measured with x-Rite eXact devices. Ultimately, the Color Muse device was rejected, and the Nix Mini 2 Color Sensor was introduced to the Fall 2020 class of 46 students. The Nix Mini 2 is designed to use 45°/0° optical geometry, a D50 illuminant with the 2° observer function, and a measurement illumination condition similar to M2 (“Compare Nix” 2020). The CIE L*a*b* values were attained through pairing the Nix sensor with an app downloaded to a smartphone.

With the eight laboratories in the curriculum, six labs tested the Nix Mini 2 for use as a measurement device. Five of the six labs proved their similarities in outcome with the results from an x-Rite eXact. These five labs covered the concepts of visualizing L*a*b* space, whiteness and opacity of different substrates, opacity of different inks, tone reproduction, dot gain, print contrast, hue error/grayness, trapping, gray balance, color balance, and the color differences in ΔE*.

Figure 1 depicts an example of classroom data sampling with the Nix Mini 2. This assignment, named “Getting started with Nix Mini 2 and L*a*b*”, aims to provide a basic understanding of the L*a*b* color space and what it means to be neutral. The test target consists of process color and overprint patches (such as Cyan (C), Magenta (M), Yellow (Y), Black (K), Red (R), Green (G) and Blue (B)). Samples used to provide this data were produced with the Konica Minolta AccurioPress C3080 on the same paper stock in one run. The activities involve students measuring the color patches with Nix Mini 2 and calculating the color difference (ΔE*) between the measurements from their Nix Mini 2 and a sample data collected using an x-Rite eXact (provided to the students by the instructors).

Figure 1. L*a*b* data collected for the Getting started with Nix Mini 2 and L*a*b* assignment

a* and b* color data collected with 43 Nix Mini 2 devices (filled small circles) in comparison to those from x-Rite eXact (×)’s. The six inserts are enlarged portions of the respective colors to emphasize the similarities and the differences.

Figure 1 shows measurements of CIEL*a*b* from Nix Mini 2 (filled color small circles) and compared to those from x-Rite eXact (×’s) on a standard a* (horizontal axis) and b* (vertical axis) plane for the colors of CMYRGB. The blowup enlargements of each color data group are shown in the figure and marked in the approximate regions that the measurement for each CMYRGB color occupy. The larger circular and square markers represent the average a* and b* of the data group for the Nix Mini 2 and x-Rite eXact respectively. For example, the cyan data displayed in the bottom left insert illustrates the comparison and contrast between the Nix Mini 2 and x-Rite eXact. As shown for the cyan colors, the mean a* and b* are -30 and -48 respectively in values for the Nix Mini 2 while -30.65 and -48.69 respectively for the x-Rite eXact. Figure 1 also shows that the precision from the x-Rite eXact is superior that of the Nix Mini 2 as the × data points from x-Rite eXact are much tighter together in a smaller area than that from the Nix Mini 2 data. This is supported by their difference in standard deviations of 0.61a* 0.26b* for the x-Rite eXact data versus 1.39a*, 1.40b* for the Nix Mini 2 data. Similar observations of other colors highlight the consistency and deviations for the Nix Mini 2 from the x-Rite eXact performance. The deviation is significantly larger with Green, as indicated by both the difference in the means and in the values of standard deviations.

Measurements and results for all tests conducted by the students with the Nix Mini 2 will be in the full paper. The overview here emphasizes the attractiveness of such portable devices in the graphic communications education.   In addition to providing the standard of learning students deserve through the pandemic, the potential of using such devices in future graphic communication virtual class designs and K-12 education could be significant.

References

Compare Nix Color Sensor Devices. (2020, November 02). Retrieved December 02, 2020,

Retrieved from nixsensor.com/compare-nix/#1519315093017-f21bfe20-6786

Kirchner, E., Koeckhoven, P., & Sivakumar, K. (2019). Predicting the performance of low-cost color instruments for color identification. Journal of the Optical Society of America A, 36(3), 368–376. Retrieved from doi.org/10.1364/josaa.36.000368