Why Do Green Trees Turn White in Infrared Photographs?

The trees are green, the sky is blue — so why does an infrared camera disagree?

Imagine photographing a familiar landscape: a leafy tree beside a river, grass along the bank and a few clouds drifting overhead.

In an ordinary photograph, everything looks reassuringly familiar.

Now photograph the same scene in near-infrared.

The foliage may appear almost white. The grass becomes pale and luminous. The blue sky turns dramatically dark, while clouds stand out against it.

It can look like a summer landscape transformed into a winter dream.

Yet there is no frost on the leaves. The camera is recording light that our eyes cannot see.

For me, this is one of photography’s most interesting possibilities: a familiar place can become a way of exploring unfamiliar science.

First, What Is Near-Infrared Photography?

Human vision covers only a small part of the electromagnetic spectrum, approximately from violet at 400 nanometres to deep red at 700 nanometres.

Beyond red lies infrared.

For this kind of landscape photography, we are interested in near-infrared, commonly recorded at wavelengths between roughly 700 and 1,000 nanometres, depending on the equipment.

The important distinction is that these photographs primarily record reflected light, usually from the Sun. They are different from thermal images, which detect longer infrared wavelengths emitted by objects at everyday temperatures.

A white tree in a near-infrared photograph is therefore not necessarily warmer than its surroundings. It is returning a strong near-infrared signal to the camera.

The Wood Effect: A Summer Tree That Looks Snow-Covered

The bright appearance of foliage in infrared photographs is known as the Wood effect, named after the infrared photography pioneer Robert W. Wood.

Despite the name, it refers to the behaviour of foliage rather than timber.

To understand it, we need to look inside a leaf.

A leaf is much more than a thin green surface. It contains layers of cells, pigments and internal air spaces. Together, these determine which wavelengths are absorbed, transmitted or scattered back out.

In visible light, chlorophyll absorbs strongly in the blue and red regions. Relatively more green light escapes, which is why most healthy leaves look green.

Beyond the visible red region, the balance changes. Pigment absorption becomes much weaker, while the leaf’s internal structure scatters near-infrared radiation strongly.

Some of that radiation passes through the leaf; some emerges back towards the camera. The strong reflection arises from repeated scattering at boundaries between materials with different optical properties inside the tissue.

The leaf’s green appearance tells us about its pigments. Its near-infrared brightness tells us much more about its structure.

That is a lovely connection between photography, physics and plant biology.

Why Does That Become White in the Photograph?

Near-infrared radiation has no colour that our eyes can directly perceive.

The camera and editing software must turn the recorded signal into something visible.

In a black-and-white infrared image, a strong signal can be represented by a light grey or white tone. A weaker signal becomes darker.

That is why strongly reflecting foliage can appear white.

However, white leaves are not guaranteed straight out of the camera. An infrared file may initially look reddish, pinkish or otherwise unfamiliar. White balance, filter choice, exposure and processing all influence the final result.

The bright foliage has a physical basis; its exact appearance on screen also involves photographic choices.

Infrared photography combines measurement with interpretation.

Why Does the Blue Sky Often Turn Dark?

The blue of a clear sky comes largely from Rayleigh scattering.

Air molecules scatter shorter wavelengths much more strongly than longer ones. Blue light is scattered strongly into our line of sight; near-infrared is scattered much less.

Consequently, a clear patch of sky can deliver a relatively weak near-infrared signal and appear dark in the photograph. Clouds scatter light differently because their droplets are much larger than air molecules, so they can remain bright against that darker background.

This creates one of infrared photography’s most striking combinations:

Pale foliage, dark sky and bright clouds.

The sky will not always become black. Haze, cloud cover, viewing direction, filter choice and editing all affect the result.

Grass, Leaves, Wood and Water: Expect Different Responses

A useful starting point is to stop assuming that an object’s visible colour predicts its infrared brightness.

Subject	Common near-infrared appearance	What to notice
Leafy trees	Bright, sometimes almost white	Species, leaf structure, lighting and canopy density affect the result.
Grass	Often pale and bright	Living grass may separate strongly from paths, soil and shadows.
Bark and dead wood	Often darker than foliage, with varied tones	Texture, moisture and surface condition matter; wood does not automatically show the foliage effect.
Open water	Frequently dark	Absorption and reflections both influence its appearance.
Clouds	Often bright against clear sky	Cloud type and lighting determine how dramatic the contrast becomes.

Water is particularly interesting. It often looks dark because relatively little near-infrared returns from within it, but its surface can still reflect bright clouds, foliage or sunlight.

A river can therefore contain both dark stretches and bright reflections.

For a Thames landscape, I would look for a composition combining leafy banks, open water and a distinctive tree. That gives several different materials to compare within one frame.

Sunlight Matters — but So Does Wind

Near-infrared photography depends on illumination.

Direct sunshine often makes a useful starting point because it supplies plenty of near-infrared radiation and can create strong separation between sunlit foliage, shadows and sky.

A bright day with some cloud can be especially rewarding.

This offers an interesting change of approach for landscape photographers. The midday sunshine that can feel harsh in conventional photography may produce striking infrared results.

Overcast conditions can still work, although the effect may be gentler and exposures may need to be longer.

Wind creates a different problem.

If your setup needs a long exposure, moving leaves may blur even when the trunk remains sharp. That can be an attractive creative effect, but it makes a scientific comparison harder.

For a first attempt, choose bright conditions and a relatively still tree.

In autumn, look for a tree still carrying plenty of leaves, or try an evergreen. Repeating the exercise as the seasons change would make an interesting longer project.

What Equipment Do You Need?

Most ordinary digital cameras contain an internal filter that suppresses infrared, helping them produce reliable visible colours.

There are two common ways to record near-infrared:

• Use an infrared-pass filter on a suitable unmodified camera. This blocks most visible light, but the camera’s internal infrared suppression may mean long exposures or very limited results.

• Use a camera converted for infrared, or a full-spectrum camera with an appropriate filter. These arrangements can record near-infrared more efficiently.

Compatibility matters: an external filter does not make every camera equally capable of infrared photography.

A filter around 720 nanometres is a common starting point for infrared work and can support both monochrome and some false-colour processing. Longer-wavelength options, such as 850 nanometres, tend towards a more strongly monochrome appearance, with different exposure requirements.

For this exercise, the aim is to use a setup known to record near-infrared reliably.

Practical Demonstration: One Tree, Three Interpretations

Your task: photograph the same tree in visible light and near-infrared, then compare both with an ordinary black-and-white conversion.

What you need

• A normal camera or phone.

• A suitable near-infrared camera and filter arrangement.

• A tripod, particularly if infrared exposures are long.

• A leafy tree, ideally with sky and another material in the frame.

• Editing software capable of producing a monochrome image.

1. Choose a useful scene

Include leaves, trunk, sky and grass. If possible, add water, a wall or a path.

The different surfaces make the comparison more revealing.

2. Take the visible-light photograph

Record the scene normally.

Note the conditions: sunshine or cloud, time of day and whether the leaves are moving.

3. Take the near-infrared photograph

Keep the viewpoint and framing as similar as possible, and photograph it soon afterwards so the lighting remains comparable.

Use settings appropriate to the infrared setup rather than copying the visible-light exposure. Check focus and the histogram, protecting detail in the brightest foliage.

4. Make a normal black-and-white version

Convert the visible-light photograph to monochrome.

Now you have three images:

1. Visible colour.

2. Visible light converted to black and white.

3. Near-infrared rendered in black and white.

That third comparison is especially useful. Removing colour from a normal photograph does not reveal infrared information that the camera did not record.

5. Compare what changed

Ask:

• Did the leaves become brighter relative to the trunk?

• Did the grass separate more clearly from the path?

• Did the sky darken?

• Did clouds become more prominent?

• Which objects changed least?

Keep the processing reasonably restrained at first. Extreme contrast adjustments can make the images dramatic while obscuring what you are trying to compare.

Turn the Experiment into a Creative Landscape

Once you understand the differences, use them deliberately.

A pale canopy can become the main subject against a dark sky. A shaded trunk can provide structure within bright foliage. A path can lead the viewer through an otherwise luminous scene.

Look for:

• An isolated tree with a recognisable outline.

• A winding path through leafy woodland.

• Bright foliage beside dark water.

• Architecture framed by vegetation.

• Clouds that balance the shape of a tree.

When editing, preserve texture in the leaves. If every bright area becomes pure white, much of the interest disappears.

Deep blacks can be effective, but the strongest image does not always need the most extreme contrast.

The question I would ask is: what does infrared reveal that makes this particular composition more interesting?

Can an Infrared Photograph Tell You Whether a Plant Is Healthy?

Near-infrared observations are valuable in vegetation monitoring because changes in plant tissue and canopy structure can affect the recorded signal. Scientists compare visible and near-infrared measurements to investigate vegetation.

However, a bright tree in a processed photograph is not, by itself, a reliable plant-health diagnosis.

Species, illumination, leaf angle, exposure and editing all affect brightness. Scientific assessment needs controlled measurements and appropriate interpretation.

For teaching, that limitation is useful. It opens a discussion about the difference between a striking observation and sufficient evidence for a conclusion.

A Familiar Tree Can Teach Us to See Differently

What appeals to me about this demonstration is that the subject can be completely ordinary.

There is no need to travel to an exotic location. A tree in the garden or beside a familiar riverside path can connect photography with pigments, living tissue, scattering and the electromagnetic spectrum.

The tree has not changed between photographs.

The wavelengths we record have changed, revealing a different set of properties.

This week’s challenge: choose one tree and make the three-image comparison.

Look beyond the white leaves. Study the trunk, the shadows, the sky and the ground beneath it.

Our eyes give us a wonderfully useful view of the world. Infrared photography reminds us how much more there is to discover.