Friday, 15 November 2013

Winter Jasmine (Jasminum nudiflorum): UV-image and bee-colours



It’s almost winter here in Germany between Darmstadt and Heidelberg. However, some late flowers can still be found outside. There are some remaining wildflowers but also late gardens species. For most of the species the main flowering season is over. In contrast to that, Winter jasmine (Jasminum nudiflorum) has only recently started to flower. The species is found in many gardens since it belongs to the few plant species that flower during the winter months.
The plant is a medium small shrub native to China and is a member of the family Oleaceae. This family includes also the olive tree.

For the human eye the flower appears mainly yellow that is a bit more saturated in the centre.

All photos were taken with a broadband-modified Panasonic-Lumix G1 that is sensitive to light of  approximately 350-1100nm.
The lens is a 80 mm enlarger lens mounted on a focussing helicoid: EL-Nikkor 80 mm /f5,6 at f11.
Flowers photographed in Bensheim, Germany 11 November 2013.

Visual light image: Infrared is eliminated by the IR-neutralisation-filter NG (Optic Makario). Capture details: 1/100s, ISO 100.

Image reference: CHA_P1110941_131111

This image displays the colours as visible to the human eye.


UV-image: Filter: Baader-U 2". Visual light and IR are eliminated by that filter. Capture details: 2s, ISO 400, UV-flash: MR21N at full power.
Image reference: CHA_P1110935_131111


The UV-image shows a strong contrast between the dark centre and the fairly bright outer petals that appear in UV-yellow. This pattern is frequently referred to as “bulls eye”.


Simulated bee-colours by pushing the spectrum visible to bees and other insects into the RGB colours space (combination of two images with different filters as shown above): UV is shown as blue, blue as green and green as red. The original red channel of the visible light image is discarded, since bees are not sensitive to most of the wavelengths contained here. The central part of the flower appears bee-red (human green) and the outer part bee-magenta (a colour composed of UV (bee-blue) and green (bee-red)):
Image reference: CHA_P1110924_RGB_UV_bw_131111


Simulated bee-colours by exchanging the red-channel with UV: The UV image became the red channel, while blue and green of the visible light image remain unchanged. Green (bee-red) is rendered as it is seen by humans. However, what appears yellow is a colour that is composed of green and UV. Since humans cannot see UV, it would appear also green to our eyes. This method generates less „false colours“ compared to the previous one but does not maintain the order of the colours that corresponds to their wavelength.
Image reference: CHA_P1110924_RGB_UV_bw_inv_131111




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