eNews Exclusive: Infrared Videography

Gone are the old days when, to represent a night scene, all one had to do is to load tungsten-type film in the camera and shoot outside fully stopped-down, to underexpose the film and to create a dark, bluish-cast scene. The resultant strong shadows were a bit unconvincing, but that was the only feasible trick for low-budget video.

Nowadays, when one thinks of a night scene, it is a grainy, greenish-tinted scene, shot in total or near-total darkness. The scene is flooded with infrared light, invisible to the human eye but very visible to the camera's CCD.

Infrared videography is in widespread use by the news media in surveillance and war footage. This, in turn, is possible due to the wide availability of IR-sensitive CCDs. Actually, standard CCDs love IR light. For normal color videography, a greenish-yellow filter blocks the IR portion of the light spectrum from the CCD. All you have to do is remove this filter, and you have a very sensitive IR detector (see Sidebar 1).

As an effect, like every video trick, infrared tends to get old rather quickly if overused. Careful use gives you some interesting and creative possibilities, which would be very difficult to achieve otherwise. A low-light level (or total absence of light) allows your subject to become less camera-aware and react more spontaneously and naturally. So overall, this is a good trick to have in your arsenal.

First of all, let's explain what IR videography is not. It is not the heat-sensing type, which really allows views of thermal radiation in total darkness, with no external illumination required. In this case, the heat of objects and bodies is enough to be detected and converted through image processing into something you can see. This is far-infrared camera work, with operating wavelengths measured in the tens of thousands of nanometers. Because of the extremely long wavelengths involved and the very high detector gain, the images are always blurred and noisy, and detailed images are not possible. Therefore, the use of far-infrared videography is mostly in the realm of police and military surveillance and astrophysics and scientific imaging.

The type of infrared photography of interest for video work (and the subject of this article) involves the use of near-infrared light. This occupies the spectrum just below red (approximately 700nm) to wavelengths slightly longer than 1000nm. These comparatively short wavelengths allow quite detailed images and the abundance of near-infrared light sources (to be discussed below) means that the final images need not be noisy.

One must be aware though, that infrared light will dramatically change the tone of an object, most obviously hair and eye tone, as shown in Figure 1. Foliage appears very bright as well, but this is all part of the infrared look. You can even use this look to create nightmarish moods, if you want.

The most common light source is solid-state infrared LEDs. You can find these in your own house in your TV and VCR remote controls. Stores specializing in video surveillance offer a wide variety of devices in different power ranges, and electronics parts stores and catalogs often sell the bulbs. If one bulb is not bright enough, you can combine them into an array. You may also need to choose the specific wavelength, if you go the home-built route. Solid-state illuminators usually come in wavelengths around 880 or 940 nanometers. The former is usually less expensive, although you may still observe a faint red glow in total darkness. The latter is completely invisible, and the longer-wavelength LEDs are typically more efficient in converting electrical current into photons, a consideration for battery-operated equipment. You might not have a choice: the bottom line is how sensitive your camera is to either wavelength, and some experimentation may be necessary. Figure 2 shows a comparison of the wavelengths of these devices compared to the spectrum of visible light.

The disadvantage of LED-based IR illuminators is that they produce a narrow beam, much like a flashlight or spotlight, and therefore will produce harsh contrast unless you give careful consideration to its location. Setting an IR illuminator is more tedious than setting its visible counterparts. As infrared is invisible to our eyes, the only way to gauge your setup is through the camera's electronic viewfinder. And some reflective surfaces that may normally appear light may be actually quite dark when seen through IR.

• Digg This!
• del.icio.us
• Technorati
• StumbleUpon
• Reddit