Colorimetric analysis of soil with flatbed scanners

Abstract

Colour is an important physical property in the characterization of soil type and the description of soil profiles. Quantitative data from spectrophotometers and colorimeters have been used in soil research for this purpose, but semi‐quantitative Munsell colour description remains the main method of soil colour evaluation. Low‐cost digital devices (cameras and scanners) could largely replace the semi‐quantitative assessment of colour by Munsell charts if such devices can be calibrated colorimetrically to provide accurate and reproducible data. Robust application of such tools, however, requires standardized light sources, which precludes the use of digital cameras as viable devices for use in the field. Flatbed scanners, on the other hand, enable 2‐D imaging by a contact method under consistent lighting conditions. Power can be provided to such scanners through a USB port by a laptop computer, so they can be used as viable devices in the field. In this study, we explored the feasibility of using flatbed scanners to derive colorimetrically accurate images and data from a set of 161 soil samples. The efficacy of our approach was tested with two low‐cost scanners, and included analysis of two commercial colour charts, six printed colour charts and three editions of the Munsell Soil Colour chart to assess the optimum methods of colorimetric calibration. For both scanners tested, we found that accurate colour characterization could be achieved for > 95% of the soil samples studied (i.e. with colour errors barely perceptible by the human eye). These results illustrate the merit and efficacy of this rapid and low‐cost approach for soil colour evaluation. Highlights Can soil colour be measured accurately with commercial scanners? Scanners can replace semi‐quantitative Munsell chart comparison or spectrophotometers. With careful calibration, scanners can be used to measure soil colour. Colour can be measured with an accuracy close to that achievable with spectrophotometers.

Differentiating Soils from Arable and Fallow Land Using Spectrometry

“…In the future, the results can be obtained using other instruments, including in the field. Although modern instruments for soil colour evaluation (spectrophotometers, spectroradiometers, and photocolourimeters) are used [10,13], digital devices (cameras) [5,8] and flatbed scanners are more accessible to researchers [6,45,46]. In this case, a constant artificial light source is used, or the photograph is taken in natural light, but using calibration scales.…”

How qualitative spectral information can improve soil profile classification?

“…There is need for employing more technological tools, including spectroscopy in soil characterization, aiming to minimize subjectivity and inconsistencies in soil classification. 15 However, a quantitative approach can only be advanced if we have a strong understanding of soil spectra. This knowledge is based on spectral intensity, shape and other features, which are closely related to soil characteristics.…”

Is It Better to Be Objectively Wrong or Subjectively Right?

“…Benchtop instruments such as spectrophotometers have been available for many years, but the necessity for sample preparation, lack of portability, and instrument cost have limited their adoption by archaeologists (but see Chenoweth and Farahani 2015; Giardino et al 1998). Instead, innovation in archaeology and related fields has focused on adapting everyday equipment, mainly digital cameras (e.g., McGrath et al 2017; Milotta, Stanco, et al 2018; Milotta, Tanasi, et al 2018; Viscarra Rossel et al 2008) and flatbed scanners (e.g., Kirillova et al 2017), for color identification. These rely on establishing calibration standards and algorithms to extract specific color data from 2D images.…”