To analyze the images, we attempt to estimate the reflectance of different objects in the image. An object that appears white in the image (more exposure of the film) will have had more scattered light (a high reflectivity) in the regime of spectral sensitivity of the camera.
In the pages which follow, the objects are first shown as color photographs to show the visible appearance of the object under illumination conditions. All color photos were taken with the same camera and under the same illumination setup as the infrared photos. Since the color images looked very similar under both Reveal and Halogen lights, only one image is shown.
The images with the infrared film, coupled with analysis, then follow. The infrared images are in general more exposed. This is because the settings of the camera had to be changed, and the picture is slightly overexposed. With the filter, less light actually reaches the film, and the image would normally come out darker with the same settings. In order to have the picture come out, the settings on the camera were changed to let more light in. Occasionally, we changed it more than necessary, resulting in the image appearing brighter.
Some infrared images were also taken with a digital camera loaned to us by Ulrich Barnhoefer. While not necessarily calibrated, the contrast between infrared and standard black-and-white photographs of the same scene are very striking, and hence we have included them. In fact, the image on the homepage of this document was acquired with the digital camera. The infrared images were acquired with an infrared filter affixed to the camera lens. In contrast with our analog photos, the digital images tended to be too dark; it is theorized that this is because the digital camera actually does have an infrared cutoff filter, just not a particularly good one.
In this section, the subsections addressing flowers, fruits, and circuits represent analog infrared photographs taken in the controlled setting of a darkroom. Accompanying these is the subsection addressing the light sources used in these darkroom experiments. The human eye photographs were also taken in a darkroom, although their analysis is less rigorous than the others; the images are included for interest nonetheless. The forest results cover infrared photographs taken in an outdoor setting. Finally, we present images taken with the digital camera; these images, while uncalibrated, do demonstrate some particularly salient features of near infrared photography.
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