EPOW - Ecology Picture of the Week

Forest and lake scene in four combinations of regular and infrared light

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.

	[A] Regular light.  Much of the forest detail on the hills is muted and unclear.  This is what the unaided eye sees.
	[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.
	[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.
	[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].
	[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.
	[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!