CIR Interpretation Tutorial
Color Interpretation of Photography in Virtual Nebraska
Most of the images seen in Virtual Nebraska, are made from color infrared (CIR) photographs. Use the following link to transfer to another page for a more complete explanation of CIR photgraphy:
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Most of the red objects that you will see in the images are actually stands of vegetation. Much of this vegetation is associated with crops on farms. The crops that are being grown on these farm fields will appear in varying tones of red. The varying tones of red can reveal a great deal of information about the relative health of the plants and whether the vegetation is sparsely or densely distributed over the landscape. Farm fields that don't have much growing vegetation on them tend to appear in greenish tones. When fields have been prepared for planting, or if the crops have just been harvested, the fields may have bluish, or bluish white tones to them. Changes in tone can suggest variations in soil texture, type or varying topography. Now, concrete tends to be white most of the time and it is most often seen as straight lines. The trick to identifying some of the bare fields from some concrete surfaces is to look at the surrounding area. If you see white squares within the city, then it's probably concrete, if it's surrounded by bluish toned fields, then it's probably just some bare soil.
Water features are usually dark in photographs such as these, but are sometimes represented in colors that range from dark blue to light cyan to nearly white. This occurs because shallow or turbid water tends to reflect more visible light than deep or clear water. The more light being reflected by a water body, the lighter in color the water body becomes.
Sometimes the colors do not appear to be uniform throughout an image. This is because
there are often several photographs that were used to create a given image.
Many of these images were put together from photographs that were not taken during the
same day, but rather over some period of time such as one or two days, or even one or two
years! This is a limitation caused by the lack of available photographs from which
we use to create the images seen on this website and it often results in a slight
variation of color throughout a given scene.
One of the most prominent features in many of these images is a very bright "spot" that is located at or near the image center. This is caused by "vignetting" (vin-yet-ing). Vignetting is the result of having a lens mount on the camera that blocks some of the light from entering the lens around its edge. This causes features away from the image center to appear increasingly darker.
Below are links to examples of some of the features that can be seen in
the color infrared imagery that is available on Virtual Nebraska.