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Adopt a Branch

Jump to [introduction] [visible colors] [visible and near infrared] [plant stress detection filter] [extensions]

Created by Lauri Twitchell from the 
University of California Botanical Garden, Berkeley, CA

In February, 2005, Lauri attended a Measuring Vegetation Health (MVH) workshop at the Lawrence Hall of Science in Berkeley. On the third day, attendees were encouraged to create their own project using MVH concepts and tools that they could use in their science center.

One of the aspects that is so exciting about Lauri's project is that by photographing this time series of leaves as one image, the lighting for all leaves was constant. This allowed for rapid comparison of the leaves using MVH software. Also, Lauri pulled from the plant shortly before the photograph, which minimized any drying effects on the leaves.

The activity below has been adapted for DigitalImageBasics software.

Introduction to Leaves on Branches

The leaves on a single branch are of a range of ages. Some have just opened, others are mature and fully photosynthesizing, and others appear to be past their productive stages and will be discarded by the plant. Can we see differences in the light reflected from these leaves of different ages?

Visible Colors

Below is a color photograph of the leaves on a branch or stem of a Nasturtium, a flowering plant. The newly opened leaf is on the left, and each leaf to the right being older than the one on the right. The oldest leaf is on the far right.

Leaves on a branch or stem of a Nasturtium, a flowering plant

Using the DigitalImageBasics software, the red, green, and blue layers of the Nasturtium photograph are displayed separately (the darker the color represents little of that color being reflected from the surface of the leaf; the brighter the color, the greater reflectance of the color from the leaf):

Leaves on a branch or stem of a Nasturtium in red light

Leaves on a branch or stem of a Nasturtium in green light

Leaves on a branch or stem of a Nasturtium in blue light

Use AnalyzingDigialImages to compare the layers of colors within the color photograph. The formula is (Intensity A - Intensity B) / (Intensity A + Intensity B).

    The color of the greater value is displayed:

    Red as a shade of Red
    Green as a shade of Green
    Blue as a shade of Blue

    This formula tends to minimize difference in illumination caused by shadows and uneven surfaces (such as crinkly or curled leaves).

    Example: using Red vs Green, if a pixel has 10% Red and 20% Green, the normalized difference is 10% divided by 30% = 0.33. This value is scaled to 33% (between the scale of 0% and 100%) and will be displayed in the computer’s Green.

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Red versus Green (normalized). Except for dying leaves, plant leaves reflect more green light than red light.

Leaves on a branch or stem of a Nasturtium with green vs blue (normalized)

Green versus Blue (normalized). Similar to above, plant leaves reflect more green light than red light.

Leaves on a branch or stem of a Nasturtium with red vs blue (normalized)

Red versus Blue (normalized). The newly opened leaf (far right) has noticeably greater red light being reflected compared to blue light. The mature leaves that are photosynthesizing best are either equally reflective in red and blue light or there is more blue light being reflected. As the leaf ages beyond this point, greater and greater red light is reflected from the leaf.

Based on this image, research is being conducted at the University of New Hampshire to correlate these red vs blue values to the amount of chlorophyll in leaves. Results and conclusions of this work will be posted when completed.

Visible and Near Infrared Photographs

The same image in near infrared lighting

This image was taken indoors, near a window, during a rainy day. Under the conditions, this is an outstanding photograph!

The landsat image of the leaves

Using DigitalImageBasics software, the different layers of the visible and infrared photographs were separated and saved as separate images (one for near infrared, one for red, and one for green). Using the SatImageMaker software, the layers were brought together to make an image that would be taken with the Landsat sensor and displayed in one of the most common color schemes (infrared displayed as red, reflected red light displayed as green, and reflected green light displayed as blue light). For more information, see the guide "Calculate Normalized Difference Vegetation Index (NDVI) from Merged Visible and Infrared Digital Photos"

Using the "Landsat" image above in AnalyzingDigitialImages, calculate and display the Normalized Difference Vegetation Index (NDVI). The redder the color, the higher the NDVI value (the maximum value is 1, which would be displayed as 100% red, and correlates with very healthy plants). Darker reds indicate that there is less photosynthesis taking place in the leaf. A black or green leaf indicates no photosynthesis is occurring.
The Normalized Difference Vegetation Index of the Nasturiums

Using the Plant Stress Detection Filter with a Digital Camera

Would the purple filter that is used as a plant stress detection device work with the Nasturtiums? What is your decision?

Image of nasturium with a purple filter

Extensions

    Use AnalyzingDigitalImages software to measure the length, wide, and area of these leaves to see if the dimensions change as the leaves progress through their stages.

    Repeat Lauri's work with plants in your garden, yard, or park. Please be responsible if using plants in parks – do not destroy the plant, especially rare ones!