It looks like another world, yet it’s not. Opening a window into a spectrum we can’t see with the naked eye, infrared photography shows us our world in an extraordinary light.
The human eye is sensitive to a range of light between 400–700nm (nanometers). Infrared exposure favors frequencies between 780-900nm, frequencies the human eye can’t see. Although we can’t see it, we are surrounded by, and often use, infrared light on a daily basis. Today, many household and office devices use infrared transmissions—remote controls, security alarms, printers, and laptop computers, to name just a few.
To be sure, rendering the invisible visible is an unusual proposition. The best we can do is to simulate it, typically by representing the invisible with a color or tone we can see. This creates some overlap between subjects that visibly contain the substitute color and those that reflect more infrared light. Both color and black-and-white film render infrared light differently. The effects of black-and-white infrared are limited largely to value (greater concentrations of infrared light are rendered lighter), while color infrared exposure adds shifts in hue (more infrared light is rendered redder and sometimes lighter).
Infrared effects depend on the scattering and absorption characteristics of materials that reflect light. The photosynthetic pigment found in plants, chlorophyll, reflects infrared light, causing these materials to appear very bright. Skin reflects infrared wavelengths while blood absorbs them, so skin looks transparent, veins sometimes become more apparent, and eyes become very dark. Sunglasses that appear opaque when reflecting visible light may seem transparent. Water and atmosphere scatter blue light and absorb infrared wavelengths, causing these materials to appear verydark.As a result, atmospheric conditions can reduce the effect of infrared significantly. The effects are often unpredictable and almost always surprising. Perhaps that is why the effect is so compelling.
You can shoot and scan infrared film. Unlike film cameras, digital cameras can provide instant feedback about how the final image will look, sometimes while you’re setting up a shot. CCDs are sensitive to the infrared spectrum up to 900nm. (Infrared film is similarly sensitive— Kodak HSI is sensitive up to 840 nm.) There continues to be a great deal of discussion about which CCD is most sensitive to the infrared spectrum. Information about this can be found at various sites on the web.
Most digital cameras can take infrared images. An easy way to determine whether a particular digital camera is sensitive to infrared is to aim a remote control into the camera lens in a dark environment. Push one of the remote’s buttons. If the camera is infrared-sensitive, you will see confirmation on the camera’s LCD screen. If there is no response, the camera is either insensitive to the infrared spectrum or contains an infrared blocking filter. The filters are used to improve the quality of normally exposed images. In most cases, the infrared blocking filters can be removed, but be careful. You risk damaging your camera and/or may void the manufacturer’s warranty.
A variety of infrared filters are available. If your digital camera doesn’t accept traditional lenses, you may have to hold or tape a filter in front of the lens when making infrared exposures. An 89B filter is a classic infrared filter that blocks wavelengths below 680nm, while allowing 50%transmission at 720nm (87 and 87C filters are other excellent choices). The 89B filter provides a window into the infrared spectrum with small amounts of visible light. For a subtler effect, a 25A red filter lets in red light. Depending on which filter is used, you may notice unusual colors in your images, which are most likely due to residual visible light.
Infrared filters can be very dense. To achieve a proper exposure, you may need to use a high ISO or a long shutter speed. A tripod is very useful in such situations. However, long exposures or high ISO may create significant noise in digital cameras. (I typically limit my exposures to 2 minutes or less with my Canon D30, since noise becomes quite pronounced with longer exposures. Your results with another camera may vary.) I recommend testing ISO settings and exposure timeswith the cameras and filters you use to determine optimum exposure and the point at which significant noise begins to occur.
Although bright conditions provide few challenges for today’s autofocus cameras, low contrast or low light conditions do, and infrared capture most certainly will.
You cannot focus through very dense filters. You may need to take the filter off the lens to focus, then reattach it after focusing. The focal plane for infrared light also is different than for visible light. To be certain you have optimum focus, preview a magnified portion of the image on your digital camera’s LCD or a laptop computer. If your lens doesn’t have distances marked for infrared focusing, test the focus settings for various distances, charting your findings for future exposures.
Making infrared exposures requires some initial testing and experimentation. Making a small initial investment in time for trial and error will pay large dividends in the future.
Unlike shooting in the visible spectrum, where color originals provide optimum results for scanned color or black-and-white images, you cannot create true infrared effects from color
originals. However, you can convincingly simulate the look of infrared exposures using Photoshop.
When trying to simulate an effect, it helps to list the characteristics you want to reproduce. With these characteristics in mind, you can devise a way to replicate them in Photoshop. To simulate black-and-white infrared, the characteristics will include a specific subject-dependent conversion to black-and-white (light foliage, dark skies), and may include a soft focus effect, created by adding noise.
The conversion from color to black-and-white is the single most important factor when simulating infrared exposures. The Channel Mixer, set to Monochrome, offers the greatest degree of control. Finding the right mix of the separate channels is essential. Light foliage would be in the green channel since chlorophyll reflects infrared light. Dark sky would be in the red channel because the atmosphere absorbs infrared light. Usually the right mix heavily favors the red or green channel, depending on subject matter.
You can strongly favor a single channel by increasing its setting to a value higher than 100%. The trick is setting negative values in one or more of the other channels. For example, try 200% Green, -50% Red, and 50% Blue. If you choose a percentage greater than 100%in a single channel, check the results carefully. In some instances, noise increases, which may not be acceptable. Generally, a total percentage equal to 100% is desired, since higher percentages can eliminate highlight detail and reduce shadows, while lower percentages can eliminate shadow detail and reduce highlights. When simulating infrared, you’ll find exceptions to this more frequently than in normal conversions to black and white.
If a desired percentage creates an appropriate tonal distribution, but has unfortunate side effects at either end of the tonal scale, try creating a Curves adjustment layer that will affect only a single channel below the Channel Mixer adjustment layer. For instance, suppose a very high percentage of the Green channel creates highlight problems. You may be able to remedy this by lowering the white point on the Green channel only. It’s unorthodox, but effective.
When simulating an infrared exposure, the mix of channels may not be determined by the subject colors; instead, the mix you choose may be determined by the subject materials. Foliage is represented with lighter tones because it contains chlorophyll. Channel mixing is hue dependent. You may have to study your subject carefully to determine its material characteristics in order to more accurately simulate infrared exposure.
Some subjects may defy simulating infrared, despite your best efforts. Lightness often is the deciding factor. For example, consider a very dark green leaf together with a bright green leaf in full sunlight. An infrared exposure would show the two leaves as being similar in tone, which would be very difficult to simulate from a visible spectrum color original. Subjects that are in dramatic light with heavy shadows also may be difficult.
You may need to use a different combination of channels for different image areas. If so, duplicate the Background layer and place the copy above the original and its adjustment layers. Then, group a Channel Mixer adjustment layer set to Monochrome to the background duplicate. Finally, add a Layer Mask to the background duplicate to reveal only the image areas that may need a different combination of channels. For example, a mix could heavily favor the Green channel in areas containing foliage, and a separate layer could use a mix heavily favoring the red channel in only the sky.
You may choose to create a soft focus effect. This can be done quickly and easily, with a high degree of flexibility and selectivity. First, duplicate the Background layer. If you’re working on a composite, create a copy of the image in its current state. At the top of the layer stack, create a new layer (Layer: New Layer). Hold the Option and Command keys down, then select Merge Visible from the Layer menu. This creates a copy of all visible layers (including adjustment layers) on a separate layer.
Change the mode of the layer to either Lighten (less intense) or Screen (more intense), then blur the new layer substantially (Filter: Blur: Gaussian Blur). Both modes simulate in-camera soft focus better because they blend the highlights into the shadows, not the shadows into the highlights.
Reduce the layer’s opacity, Opacity settings vary depending on the blending mode selected. This effect can be masked (Layer: Add a Layer Mask: Reveal All), then selectively reduced by painting the mask on with a black soft-edged brush set to varying opacities.
You may also choose to simulate the grain found in a majority of infrared exposures. Keep the noise introduced to digital files on a separate layer. Keeping effects on separate layers allows you to modify them in the future, or return to the untouched original. To create grain or noise on a separate layer, create a new layer. Set the blending mode to Overlay and check the Fill with Neutral Color box. This creates a new layer filled with 50% gray. However, that value produces no visible result due to the blending mode, but any lighter or darker value will produce results.
Filter the layer (Filter: Noise: Add Noise or Filter: Texture: Grain). Reduce the opacity of the layer for a subtler effect, or scale the layer to resize the noise. If unwanted color artifacts are introduced, group a Hue/Saturation adjustment layer with the saturation set to –100 to the effect layer. Reducing the opacity of the Hue/Saturation adjustment layer reduces the desaturation of the noise effect.
Black-and-white infrared photography is prized for its otherworldly appearance. True infrared exposure requires considerable testing. Digital capture makes testing efficient, and can save time and money. You can simulate the surreal qualities of an infrared exposure by using color exposures done in visible light. You gain considerable control and predictability in the process. With two new choices available, you might want to use one to help make decisions with the other.