Sensing chlorophyll, carotenoids and anthocyanins concentrations in leaves with spatial resolution from digital image

GABRIELA B. CORDON; MARÍA GABRIELA LAGORIO

Color in Food: Technological and Psychophysical Aspects

CRC Press (Taylor and Francis Group)

Año: 2012; p. 121 - 132

The aim of the present study is to develop a methodology to infer pigments concentration in leaves (spatially resolved) from a digital image of the material. Uniformly coloured leaves of different species were selected. Reflectance spectra of these leaves were then obtained from 300 to 700 nm, using a spectrophotometer equipped with an integrating sphere. Barium sulphate was used as 100% reflectance (white reference). Seven reflectance spectra were averaged for each species and the resultant spectrum was used for further derivation of coordinates (R, G and B). The selected species were: Hedera helix, Liquidambar styraciflua, Populus alba, Rosa sp., Gardenia jasminoides, Schefflera arboricola, Aloysia triphylla, Ficus benjamina. On these leaves, chlorophyll-a, chlorophyll-b, carotenoids and anthocyanins were determined by extraction and posterior spectrophotometric measurement. From the reflectance spectra of uniformly coloured leaves, and taking into account a standard illuminant, the RGB coordinates were calculated. Then, correlations between the colour coordinates and the pigment concentration in mmol/cm2 were obtained. Values for the R component decreased non-linearly as chlorophyll concentration declined. Values for G component decreased linearly with chlorophyll content. Values for the B component, on the other hand resulted insensitive to chlorophyll concentration. An excellent correlation was finally found for the sum of R and G with the chlorophyll content and between the ratio R/G and the proportion anthocyanins/chlorophyll. No correlation was found for carotenoids. On the other hand, images from heterogeneously coloured leaves (Liquidambar styraciflua, Ligustrum vulgare and Schefflera arboricola) were captured using a commercial scanner (HP-DeskJet F380 de Hewlett-Packard). The scanned images in TIFF format with a resolution of 300 ppp and a depth of 24 bits were digitally processed using the ERDAS IMAGINE 8.4 program. Using this software the TIFF images were imported to IMG format and they were subsequently separated in R, G and B bands. Using the correlations between the colour coordinates (R, G and B) and pigments concentration, deducted for homogeneous leaves, the concentration of pigments per pixel in heterogeneous leaves were estimated.