Tracy's Near Infrared Glamour & People Photography
History:
It was in the 1800's that Sir William Herschel found out about Infrared when he was measuring the temperatures of bands of color as they came out of a prism. The color just beyond red wasn't visible and yet registered even hotter than red. Then in 1910 William woods published regarding infrared photography in London. We are still discovering some amazing things about this range of energy invisible to our eyes. This page is more my own notes in photography and the results of near infrared (from here on called NIR) in images and not how to process them. I welcome any feedback that can be presented in laymen's terms. Each photographer will have their own style of processing but this page is about the phenomenology of NIR in photography.
Many use converted digital cameras to see infrared and create images that look out of this world. Infrared began with infrared film cameras many years ago by the military. It was used to distinguish between materials that looked similar but were not. The overall strength of infrared is that you can have three objects such as three dresses all made up of black cloth side-by-side but the infrared could possibly tell them apart if the materials were different. For instance if one was cotton, one was nylon, and the third was leather. Each would show entirely different brightness in the infrared image. The leather would show up extremely dark while the cotton would show up very bright. Meanwhile in the visible image each of the outfits were still jet black to our eyes.
When we talk about infrared there are often terms that get mixed together in ways they shouldn't. For instance many people think of thermal images when they hear the words infrared. Thermal is the longest parts of the infrared spectrum and generally not part of popular photography. Infrared is really a stretch in the infrared spectrum and divided into a few categories having different properties. Here is a fast summary of what I mean...
- Normal visible spectrum looks from .4 to .7 microns (also said as 400nm to 700nm) common camera detection range.
- The Near infrared (NIR) region about 0.7 to 1.1 microns (also stated 1100nm and the upper detection limit for silicon based cameras)
- The Short wave infrared (SWIR) band about from 1 to 3 microns (non-thermal and above hobby camera detection, sees through smoke)
- --Note that indium gallium arsenide cameras (InGaAs) go up to 1700nm/1.7 microns and are not the type in hobby photography, yet?
- --Note that lead sulphide based cameras detect up to 2500nm but all detect items above 392 degree fahrenheit
- The Medium wave infrared (MWIR) band about from 3 to 5 microns (thermal)
- The Long wave infrared (LWIR) band about from 8 -12- 14 microns (thermal) jumping numbers for skipping absorption bands
The most interesting draw toward NIR for photographers is how plants appear. NIR has an interesting response when it encounters moisture or moisture beads. The huge vegetation response and how plants look brighter in NIR is what drives the unique backgrounds for my people images. Farmers use the NIR to determine crop health. In a measureable way the better watered the plants are the more they reflect in the NIR.
How getting bright plants on the image works...
At the heart of this beautiful phenomena are cells in plants and how they more reflect and transmit Near infrared (NIR) than absorb. NIR energy bounces down into the tubes of tree leafs where the plants convert red and blue light into energy the plant can use (giving back green as you see in tree leafs). Instead of being converted as blue and red energy normally do, the NIR keeps traveling further downward into the plant leafs until it hits the water beads within the leaf (In geeky terms the NIR goes through the upper epidermal cells and palisade mesophyll cells but then bounces off the spongy mesophyl cells or water and air conversion area). At this point NIR comes back out of the plants in great quantity. This makes the plants look very bright compared to the dark green we are familiar with in the visible spectrum. This occurs because of the water the plant retains. The small cells in the leafs are like mirrors when filled with water. When the cells collapse because they are dry then less NIR energy comes back and the color appears more subdued. If one were to flatten a leaf out with a rolling pin and let it dry the result would be a very dark leaf in infrared.
[] Lawn grass has one of the highest reflective response curves of any vegetation in the NIR. This is in proportion to how often it gets watered.
Heavily watered lawn grass has one of the highest near infrared return of any vegetation
[] Year-around trees such as pine trees (called coniferous) are more subdued or darker than broad leaf trees quite often in NIR. It's noted that broad leaf trees (deciduous) reflect even more than 80% of the energy back at the camera many times. That is because each layer of broad leaf tree canopy reflects energy back a little more that went through the previous layer of leaves. Simply said if the NIR energy goes through one leaf in a multiple canopy forest, then there is a chance it will be reflected at the next layer and so on. This is opposite what we see in visible light as much of the light is absorbed giving back shadows and dark green in a forest. Many NIR images give back so much the tree scenes are mistaken for winter snow covered trees.
Notice the darker returns in the coniferous in the background to the left
versus the bright deciduous leafy tree on the upper right
Dead leaves soak in water puddles along the trail
[] Chlorophyll appears to play little part in reflecting infrared energy. For instance these leaves have died and fallen off the trees. They are also void of the color green indicative of chlorophyll. Yet the leaves return enough infrared energy to make them bright as they soak in the water puddles next to the snow on this dirt trail.
[] When cameras are converted to infrared a filter is also removed called the anti-moire filter. This filter that applies a slightblur to the light before it reaches the sensor to minimize striping effects. Removing the IR blocking filter removes the anti-moire filter as well. This produces images that are sharper unprocessed than before. Notice the cage by the road in the image above that is normally for protecting service equipment. The anti-moire filter removed adds a bit more contrast to the images. The down side is that anytime you get near checker board patterns or lines the moire effect will show up on your images in an undesirable way. Notice the sides of the buildings as an example and the asliasing due to no moire filter.
While the sun is bright and reflecting off the clouds the sky still appear dark as if near sunset
[] The sky seems darker and even black as you go upward with the clearest of skies. Regular light bounces off the sky in visible and comes back as blue. The NIR light keeps going into space leaving a dark contrast. Clouds contrast greatly and appear sharper because of this attribute. One can tell when a camera captures other than pure infrared because blue skies come back into the image. Full spectrum infrared is an example of this.
[] Clouds glow brighter in the NIR because water droplets inside of clouds return the energy back.
[] Multi-bounce is a phenomena I've not read about regarding infrared but have discovered in my photography recently. This now seems like common sense when I look back. Since the vegetation is reflecting the light and basically becoming it's own light source it acts as sort of a house of mirrors. In this way the image below looks like someone is holding a reflector under the models face. This minimized most of the shadows but only in the infrared image. In the visible the dark shadows are more dominant. Moreover when photographing in a canopy covered forest area the images became over exposed and the light intake had to be dialed down. What was happening was that as light bounced off one tree in the canopy cover it would bounce to another and so forth like a house of mirrors.
Shadows are minimized because of the secondary bounce of NIR off the grass
Only a short distance away from the other shot this slight canopy
of trees creates a radiating light shot from multi-bounce
The belt and bow are dark in visible light and bright in the infrared
[] NIR energy goes down into the skin millimeters before coming back out. The depth the NIR penetrates ones skin seems to depend on pigmentation and many other factors still being researched. This ability also explains why dark skin appears bright as well as the next couple of observations.
[] People's skin looks milky or like a wax statue in softness and loses detail. Many of the bumps and blemishes don't show up in the infrared. In many cases it's the most flattering skin photographs you can have aside from the pale outcome.
[] Tattoos on skin are more contrasted as NIR bounces down into the skin and back out. Ink that blurs underneath the skin is detectable. The tattoo images were 'equalized' to show the tonal range detected.
[] Veins under the skin are easily detectable but hardly show in visible light at all. Can someone's thicker veins indicate more oxygen being carried through the system? In hospitals they have pulse and blood oxygen monitors. These monitors are put over the the finger or ear. These devices transmit light wavelengths in the infrared. The machine then compares the two wavelengths and the oxygen content of the patient’s hemoglobin can be calculated. Some companies are also using this like a finger print identification since people never have veins in the exact same place.
[] Since infrared bounces under the skin it can show the shaving stubble on even a cleanly shaved face
Cleanly shaven face shows stubble in the infrared
[] The eyeball of each eye often shows little catch-lights or reflections giving a sinister appearance unless there is direct flash.
[] Eye "contacts lenses " reflect NIR energy and therefore are detectable as seen below.
[] Eye-liner, eye-shadow, and eyebrow pencil absorb infrared energy, leaving dark areas as they intended in the visible spectrum as well.
[] Dark shadows under and above the eye vanish in the NIR. So the entire eye area looks differently.
[] Sun glasses appear transparent since most are for blocking visible light and UV rays but not the longer infrared wave.
[] Darker and softer-skin such as lips and areolas tend to blend about the same color as the surrounding skin.
[] The whites of the eyes reflect a blood-shot look.
[] The Teeth reflect dull.
[] Dark hair reflects a lighter color. Note hair wigs show as pure black in the NIR.
[] Eyelashes and eyebrows tend to blend in slightly more for a unique appearance. Like hair they reflect a lighter tone.
[] NIR penetrates fabrics differently than visible light. Some clothes are more translucent than others in the NIR. The t-shirt in the image below is pure black cotton but translucent in the NIR. This image was taken without realizing the fabric involved but nothing was revealed so makes a good example. Supposedly this effect was noted when Sony produced a camcorder that was abused by people running down to the beach playing x-ray vision so-to-speak in its use in the late 1990's.
[] The NIR region is reflective. That is to say that what you see is very much affected by the sun. In a situation where it is totally overcast and very little sunlight you'll find the images look grainy with low contrast.
[] The bottom of people's feet falsely appear dirty because less energy comes back from less moist skin.
[] Traffic lights will not appear in pure NIR because many times the city exchanges the expensive and hot lights for more cost efficient light emitting diodes (LEDs). LEDs give off a very particular range of light and in most traffic lights this is visible light only.
The infrared often distinguishes materials that appears the same in visbile light. The straps are probably not leather.
Summary:
For the simplification summary the NIR reflects brightly when it encounters moisture (water droplets). Summer vegetation and greenery make for the most amazing landscapes in infrared because they are watered and healthy. The very nature of NIR requires very bright light and preferably sun light for a good photographed image. When photographing an NIR image it's best if the weather isn't too perfect or else you may be left with a huge black sky behind the subject. Those storm threatening days with bright sun still behind the camera are incredibly helpful in getting an excellent image.
If you are a model trying to understand the look of outfits in the infrared images here is some short explanations. Look at the items in the image not as "colors" because nobody's eye sees in the infrared. It is more about infrared energy and how that energy goes from the sun and bounces back to the camera after shining on objects in the image. Some things are bright and some things are dark. Remember however that all the rules about infrared energy are not necessarily the same as the visible you are used to seeing. Sure some are the same for instance, cold snow comes out pure white in infrared so we can say all the infrared energy we are detecting in sunlight bounces off snow and comes back at the camera. However, green trees come out dark green in the visible and yet bright in the infrared. The pine trees remind us that not everything relates to what we are used to seeing. The opposite is leather and eye-liner which appear to absorb all the infrared energy and show pure black to the camera just like in visible. In infrared odd things can show up too. Since the threads on a leather jacket are not leather they often show much brighter all the way around the seams. One wouldn't see these threads in the visible. Now the in-between gray tones are the "colors" are chosen by the photographer but how bright or the intensity of these objects is really what is coming back into the infrared camera. Black hair is often not that dark in the infrared and therefore is a lighter tone in the infrared images. You'll find that most common black clothes come out in a lighter color on infrared. Remember the type material and different type dyes being photographed often determines how it shows up in infrared and not necessarily the change in color-dyes put into the fabric seen in the visible.
Threads in the leather jacket are black in the visible but reflect differently in the infrared image to the right
Written Apr09 and updated June 2010 by Tracy Rose