False Color Infrared Photography
with a Webcam
John F. Green
False color near-infrared photography
was invented by researchers at the Eastman Kodak Company
during World War II for the purpose of camouflage detection.
The method was based on the fact that living vegetation
reflects near infrared sunlight much better than artificial
vegetation and camouflage paints and netting. It has since
been shown to have many other uses.
Near-infrared photography is widely used
for aerial photography, because it eliminates the blue
haze that is characteristic of the atmosphere. It is often
capable of discriminating between healthy and diseased
or stressed vegetation. It can detect certain types of
water pollution. It is sometimes used for artistic effects
by photographers.
Special films, filters, and handling
techniques must be used with color infrared photography.
For example, color infrared film must be stored in a refrigerator
or freezer, loaded and unloaded in total darkness, and
developed within two days after exposure. Thanks to electronic
imaging technology, all this can now be avoided.
Here I will describe a procedure that
uses an easily modified Webcam and an inexpensive infrared
filter that closely replicate the results provided with
false color infrared film. Please note that we are dealing
here with near-infrared radiation, not with far- or thermal
infrared which is used for nighttime surveillance, thermal
imaging, etc. I mention this because I find that people
often seem confused on that point. A webcam won't help
you find a fugitive in the dark unless you are illuminating
the scene with short-wave infrared light.
Figure 1. Flowers in false color infrared.
R ADJACENT TO FIG.
1 ABOVE.] 
Figure 2. The same flowers in Fig. 1
in visible light.
The human eye can detect the optical
spectrum from about 400 nanometers (violet) to about 700
nanometers (red). Our visual system perceives this range
of light wave frequencies as a continuous rainbow of colors.
Charge-coupled devices (CCDs) are light sensor arrays
that respond from the blue to about 1000 nm in the near-infrared.
The range from 700 to 1000 nm falls within the near infrared
region of the spectrum.
Because of the high sensitivity of CCD
sensors to near-IR, digital camera manufacturers usually
place a filter that transmits visible light but blocks
near-IR between the lens and the CCD. The absence of such
a blocking filter was the basis of the so called X-ray
vision modifications to video cameras a few years ago.
In order to use a camera for near-IR applications, this
filter can with some effort be removed, but this step
is usually unnecessary because the filter does not block
all the near-IR.
How to Make a
Near-Infrared Image
The technique I have developed for making
near-IR images is fairly simple. It requires a double
exposure, so a tripod or some means of rigidly mounting
the camera is required. Having a laptop computer is very
helpful for outdoor work. I have used an IBM PC Cam (XVP600)
and a Logitech ClickSmart 510 and have received similar
results with both. Depending on the specific camera your
results may vary.
The procedure is as follows:
1. Compose your scene. For initial experiments,
I suggest an outdoor scene with green vegetation and bright
sunlight.
2. Make the first exposure.
3. Without moving the camera, place an
IR filter over the lens and repeat the exposure. I usually
let the camera software determine the exposure, which
it generally does tolerably well.
4. Once you have the pictures, load them
into Adobe Photoshop or any other photo editing program
that allows splitting an image into separate color bands.
Create a new, blank 640 x 480 RGB image (or the size your
camera uses).
5. Next, go back to the image taken with
the IR filter. In the Photoshop menu, select Channels.
Select the red channel. On the Select menu, click on Select
All. Copy it to the clipboard. Select the new image, select
the red channel and do a paste. Now select the image taken
without the filter. Again select the red channel, copy
it to the clipboard and paste it into the green channel
of the new image. Now repeat the process with the green
channel of the normal image, this time into the blue channel
of the new image. In other words:
a. IR red channel to new red channel.
b. Normal red channel to new green channel.
c. Normal green channel to new blue channel.
6. Now when you click on the new image
RGB channel, you should see something resembling a false
color infrared image of the scene. This is similar to
the way false color infrared film works though it uses
a CYMK (Cyan-Yellow-Magenta-Black) scheme while here we
are using RGB (Red-Green-Blue). At this point you may
want to adjust the colors slightly with the adjust feature
under the image menu of Photoshop.
.] 
Figure 3. Scene showing a typical near-IR
false color view of of healthy vegetation (red).
Exposure Time and Near-IR Filters
You will find that a considerably longer
exposure (as much as several hundred times) is needed
for the picture with the IR filter in place.
Infrared light will come to a focus slightly
before the image plane compared to visible light, but
since most webcams have such small lens apertures, this
can usually be ignored unless you are doing close-up work.
In this case experimentation is probably your best bet.
Some experienced photographers suggest focusing 10% short.
I use a simple, cheap IR filter from
Edmund Industrial
Optics (Stock No. H43-948). This filter is not intended
for imaging applications, but at 640x480 pixel resolution
it is more than adequate. Many other kinds of filters
are also available from this supplier.
An inexpensive near-IR filter, I am told,
is a frame of unexposed but developed positive transparency
(slide) film. If one is interested in better quality,
there are a number of near-IR filters made for this purpose
available from photography suppliers. I won't go into
a lot of detail about filters because many different filters
are available and the correct choice depends heavily upon
the particular situation.
I mentioned above that one can remove
the camera's IR blocking filter. In this case, however,
you will have to find some way of replacing it or a similar
filter somewhere in the optical path while making the
normal exposure. The filter removed from the camera will
in most cases be too small to be conveniently used in
front of the lens. Removing it and using a replacement
in front of the lens, however, will considerably improve
your results, because by leaving it in place you cause
the CCD to sum some visible light with the infrared.
Figure 4. The image on the left was taken
with the cameras infrared blocking filter removed while
that on the right was taken with the filter in place.
Note how bright the vegetation is and how dark the water
is on the left.
Going Further
There is no reason this procedure cannot
be used with more elaborate digital cameras, though I
would be reluctant to disassemble my digital SLR. Some
digital photographers have been venturing into the infrared
(and even ultraviolet) realm for years with spectacular
artistic results. Digital cameras have opened new pathways
into a fascinating and often beautiful world beyond the
range of the eye to those willing to experiment and perhaps
break a rule or two now and then.
Plugging infrared photography into your
browser search line will bring up a lot of reading material.
For example, here are a couple of interesting web sites:
http://folk.uio.no/gisle/photo/ir.html
http://www.naturfotograf.com/uvstart.html
