Explanation:
For decades, infrared-sensitive film has
been used to image forest and other vegetation. Infrared
(IR) satellite images are used to identify
deforestation,
regional
variation in vegetation,
farmland productivity, forest
fires, riparian
and river vegetation, and other uses. I
thought it would be interesting to experiment with various ways to photograph
a forest scene in regular and infrared light, to see which brings out the most
ground-level detail in the vegetation. The scene is a second-growth
Douglas-fir and hardwood forest along a lake on the Oregon coast. It was
a cool, mostly overcast February day and shadows were muted. Here is a
progression of images showing increasingly finer detail. Click on each
image for a larger version.
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[A] Regular light. Much of the forest detail
on the hills is muted and unclear. This is what the unaided eye
sees. |
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[B] Infrared light. Now some forest
vegetation details appear on the hillside, including the lighter patch
of hardwoods on the right and the conifers on the left. Note also
greater detail in the clouds. |
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[C] Infrared light, with long (2-second) exposure.
More details yet. The IR filter is very dark, so forcing longer
exposures produces more contrast and greater detail. |
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[D] Infrared light, long exposure, converted to
grayscale. I basically converted photo [C] to grayscale and
slightly enhanced the gamma and contrast, for a more "normal"
appearing photo, but with much detail. Compare with photo [A]. |
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[E] Regular and IR light stacked. Here, I stacked
the regular-light [A] and IR light [B] images for a more normal
appearing sky and lake but to bring out forest vegetation detail. |
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[F] Regular and IR stacked, converted to grayscale, and
enhanced. Here's the best image with the most detail; it's
image [E] converted to grayscale with enhanced gamma and contrast.
Compare with regular-light image [A]! |
Detail of the forest vegetation largely not visible under regular light and
the unaided eye appears under long-exposure with the infrared filter [image C
above]. Converting this to grayscale produces a more natural-appearing
image [D]. And stacking the IR and the regular-light images produces the
most interesting image with great detail of the forest vegetation and contrast
of the lake. Here is the full, uncropped image:
Information:
I took the photos on this week's EPOW with my Sony DSC-S85
digital camera
(4mp) using a Hoya 52mm Infrared Glass Filter. This filter passes only
infrared rays above 720nm. If you use infrared-sensitive film in a film
camera, you will also need to use such an infrared filter too, because
infrared film is also sensitive to ultraviolet rays and the shorter
wavelengths of the visible spectrum, so it is necessary to filter out all but
the infrared rays.
I stacked the IR and regular images by using the
brighten function in the shareware program
Image Stacker by Tawbaware
Software. The brighten function uses the brightest pixel from each
image, thus enhancing both the forest vegetation and retaining ripple detail
of the lake water in the foreground.
Did you know that
digital cameras are inherently sensitive to infrared light and often have
built-in filters to mostly block it? Try using your digital camera to
photograph the otherwise invisible infrared light beam from your TV remote
control unit. Point the remote control directly at the camera lens, hold
down one of the buttons on the unit such as for volume, and snap a
photo. You will likely see a glowing red LED light in the photo!
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