At the first glance, a monochrome picture taken in infrared may look similar to a black and white photograph. And then you start seeing differences: objects which are bright in visible light (like sky) look dark here, while some of those which are "normally" dark (green foliage) acquire a bright glow. Indeed, the most dramatic difference between the visible and infrared spectrum is in case of foliage, with the foliage becoming very bright in infrared.
It turns out that most digital cameras are quite capable of capturing infrared light. The trick with taking digital infrared (IR) pictures is to put an IR filter on the camera. I use a Hoya R72. What the filter does is block almost all of the visible light and passes ("lets through") a range of IR light that you cannot see.
Look at how the leaves on the trees aren't as dark as you would expect green leaves to be. This is because the leaves are reflecting a large amount of IR light from the sunlight your eyes do not process.
In the first 2 pictures below, you can see the tree leaves and the lawn are very bright. The metal park bench is dark because the bench does not reflect much IR. The clouds are light and the sky is quite dark. The clouds are very reflective and transmit Near-IR quite well. The sky is darker because it does not contain much IR. It is also colder, as temperature does play a role, (though minor) in Near-IR image taking.
I believe the most useful, general-purpose IR filter for digital photography is Hoya R72. It blocks visible light well enough (if not entirely) to provide a well-pronounced IR effect, while still allowing for non-exotic exposure times. This filter should work fine with most of mid- to high-end digital cameras (your mileage may vary, so check with someone who tried it on your camera). The small amount of visible (far red) light which this filter lets through does not affect pictures enough to spoil the IR effect, while coloring your images red (or purple), therefore they need to be converted to monochrome in postprocessing.
I have taken a number of shots to compare the difference between visable and infrared. I would take two shots from the same location, one in visable and the other in IR. For the IR shot I used Hayo R72 filter. Below are two of the shots I made for this comparison. For more comparison shots, Click Here
Basic Technique
The technique for making an infrared image is quite straightforward. Although I will describe this in terms of the Pentax K100D, other cameras will have similar issues and solutions.
The first step is to compose your photograph, using a tripod, and with no filters attached. The filter is almost completely opaque, so composition must be done beforehand. You must then screw the filter on without altering your zoom settings -- sometimes a tricky business. The tripod is necessary to hold the camera in place to attach the filter, and to allow you to make very long exposures -- possibly several seconds in length.
Color isn't even a meaningful concept in the IR band, but color recording is still your best bet for high-quality IR work. It is possible to record your image using black and white recording, but you’ll have more control and more options in post-processing with color recording, and you won't have burned bridges with a simplistic in-camera grayscale conversion algorithm.
Focus can be an issue with infrared, since infrared light focuses at a slightly different spot than visible light. Older lenses had a red spot or the letter R (in red) that indicated how to adjust focus for infrared, however, my more recent auto-focus lenses don't have this feature. The red spot indicated that you have to focus closer than with visible light -- for example, for a 7 foot object, you would focus at about 5 feet (of course, this is very approximate). To avoid this problem, I use the auto-focus feature on my K100D. With the Hoya R72 filter installed on the camera, the viewfinder appears black when you look though it. However, the CCD ‘sees’ the IR and can automatically focus.
The next step is to set the ISO to 400 or higher. The filter is so dark, that even at 200, I have to use very slow shutter speeds to make an image, especially using f/11 to f/22. Of course, photographing with bright sun helps, but don't limit yourself to bright sun conditions. Shutter speeds of 1/15 to 1/2 second in direct sunlight is quite common.
To make a proper exposure, I have found that I have to use exposure compensation of anywhere between +1 and +3. Typically, I use +1 when the sun is bright, but higher adjustments may be helpful when the sun is behind clouds. Fortunately, you can use the histogram to check the image out, and make immediate adjustments. Don't be fooled by the look of the image on the LCD. Use the histogram to make sure that the exposure is balanced appropriately.
Lastly, I prefer to use the camera's RAW format. I want to use as much image information during processing as possible, and this is accomplished with RAW format. However, to create a monochrome image it is not necessary to use RAW, for a monochrome image you can use the more common JPEG format.
The final tip before tripping the shutter is to cover the viewfinder. Stray light coming in the viewfinder can significantly alter the exposure.
The final steps are done in the computer. First, you must change the color to a black-and-white type image for processing.
Infrared red requires digital modification to bring out a 'good' picture. When using the Pentax K100D, the unprocessed IR shot taken directly from the camera is very red. Below is the shot when it comes straight out of the camera. The red tone can be varied by adjusting the white balance before taking the shot. But since infrared is near the red portion of the visible light spectrum, the CCD sensor records the shot so it appears red when we view it after processing by the camera.
There are numerous ways to process the infrared image obtained using your digital camera and a Hoya R72 filter. There are two methods I would like to describe, one yields a monochrome image and the other yields a color cast image. Part 1 listed below describes a method using Photoshop Elements to yield a monochrom image. Photoshop Elements is a realtively inexpensive program for digital photo processing. Part 2 describes a method to use Adobe Photoshop to create a color cast image.
Part 1 - Creating a Monochrome Image
The photo just below is the unprocessed image directly from the camera.
You’ll want to manipulate the shot a bit to make it better emulate the look of infrared film. With Photoshop Elements, try the following:
1. To remove the red color, from the menu select Enhance > Adjust Color > Adjust Hue/Saturation and decrease the saturation to -85. Alternatively, you can also choose Remove Color from the Color submenu on the Enhance menu to go directly to a black and white image, but this doesn't generate the best results.
2. Next balance the image color levels from the menu Enhance > Adjust lighting > Levels. Adjust the RGB levels by sliding the right adjustment triangle to the left.
3. Now to lighten the image, from the menu choose Enhance > Adjust Color > Adjust Hue/Saturation. Decrease Saturation a little and increase the Hue to yield the following.
4.We’re nearly finished. The results so far will probably be a bit soft, so from the Menu choose Filter > Sharpen > Sharpen. I also think the shot could be cropped to remove some of the top and bottom of the shot.
To finish the decription of the IR shot I posted above. After cropping and color correction using Photoshop Elements, I also noticed a dust spot in the sky. This can be fixed with a clone tool.
The sky also displays a lot of noise. The noise can be reduced using the progam Neat Image (search Neat Image on Google - there is a free version) you can download. Anyway, after using the clone tool in Photoshop and Neat Image to reduce the noise the shot looks like this.
Digital photography is a lot of fun, but exploring infrared with a digital camera adds a whole new dimension. For a few bucks, the cost of a Hoya R72 filter, on top of your digital camera, you can really have some fun.
See Part 2 for a method to create a color cast image like the one below using Adobe Photoshop.
