Quantifying Plant Colour and Colour Difference as Perceived by Humans Using Digital Images

Abstract

Human perception of plant leaf and flower colour can influence species management. Colour and colour contrast may influence the detectability of invasive or rare species during surveys. Quantitative, repeatable measures of plant colour are required for comparison across studies and generalisation across species. We present a standard method for measuring plant leaf and flower colour traits using images taken with digital cameras. We demonstrate the method by quantifying the colour of and colour difference between the flowers of eleven grassland species near Falls Creek, Australia, as part of an invasive species detection experiment. The reliability of the method was tested by measuring the leaf colour of five residential garden shrub species in Ballarat, Australia using five different types of digital camera. Flowers and leaves had overlapping but distinct colour distributions. Calculated colour differences corresponded well with qualitative comparisons. Estimates of proportional cover of yellow flowers identified using colour measurements correlated well with estimates obtained by measuring and counting individual flowers. Digital SLR and mirrorless cameras were superior to phone cameras and point-and-shoot cameras for producing reliable measurements, particularly under variable lighting conditions. The analysis of digital images taken with digital cameras is a practicable method for quantifying plant flower and leaf colour in the field or lab. Quantitative, repeatable measurements allow for comparisons between species and generalisations across species and studies. This allows plant colour to be related to human perception and preferences and, ultimately, species management.

No sex-related dispersal limitation in a dioecious, oceanic long-distance traveller: the bull kelp Durvillaea antarctica

“…In this manner, the colour analysis remained objective and quantifiable, as opposed to a previous study where colour variation was only described qualitatively (Collantes et al 1997), leading to possibly unreliable results based on the use of various systems and observers (Kendal et al 2013). The blade pieces were photographed within 24 h after sampling in order to exclude the risk of colour variation caused by the drying of the samples.…”

“…The method used to quantitatively express the colouration of the images was red, green, and blue (RGB) values, which can define any given colour (Zhang et al 2014). Although this is a rather common way of representing colour, it is important to note that RGB values are rarely standardised and vary according to the instrument used to obtain the image (Kendal et al 2013). All images were taken using a Canon EOS Rebel T3i Camera at a distance of 50 cm from the sample and the RGB values of these samples were obtained using Adobe Photoshop Lightroom 5.3.…”

Optimal Altitude, Overlap, and Weather Conditions for Computer Vision UAV Estimates of Forest Structure

“…Beijborn et al [79] used image features to automatically classify coral communities. Image features have been used for automatic detection and classification of leaves and flowers [80,81]. Recent research has also extended the use of image features and classification for 'geographic image retrieval' from high resolution remote sensing images [58].…”

Flower Colours through the Lens: Quantitative Measurement with Visible and Ultraviolet Digital Photography

“…Recently, one study proposed the use of digital photography as a tool for the characterisation of plant signals in studies of diversity, conservation and plant-pollinator relationships [23]. However, the approach it described is limited to expressing camera responses in a purely human-based colorimetric system which significantly differs from the way most insect pollinators perceive flowers [15], [34].…”