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Method Development I

  • We identified four pixel classes in our images: green (leaves), purple (leaves and flowers), residue, and soil (Figure 1, left window).
  • To facilitate sampling pixels from images, we wrote a macro for ImageJ that records x and y position and red, green and blue color density for each pixel selected (Figure 1) (link to macro - "Color Saver").
  • We sampled the color of 10-15 pixels per class per image for 2-4 images from a given batch (same plant species, images acquired on the same day). We intentionally selected pixels to represent the full range of each of these color classes.
  • Samples of pixels from each class revealed differences in coloration that could be used to classify pixels (Figures 2).
  • We graphed the sampled pixels by class using various combinations of colors and color ratios. We found a broadly similar pattern for most of the images we sampled, though the exact threshold values varied depending on crop growth, lighting condidtions and exposure, and camera.