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(a) The Region of interest (Red rectangle) should be specified using the original size spectral photograph (Magenta frame). (b) We have cropped the Region of interest (Yellow frame) from the original-size spectral photograph, and then, the resulting image was used to specify the Square aperture (Red rectangle) and the Square usable (Magenta rectangle). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
