Consumer-grade Digital Camera Research Articles

A comparison of digital and film fisheye photography for analysis of forest canopy structure and gap light transmission

Due to the scarcity and high cost of conventional film-based hemispherical photographic systems, some forest scientists are now using multi-purpose, consumer-grade digital cameras for the analysis of forest canopy structure and gap light transmission. Although the low cost of digital cameras and direct capture of digital images appear to offer significant advantages over film camera systems, relatively little is known about their technical differences from an applications perspective. In this study, we compared the performance of a popular digital camera (Nikon Coolpix 950 with FC-E8 fisheye) with a conventional film camera (Nikon F with Nikkor 8 mm fisheye) under different stand structures and sky conditions. Our findings show that the Nikon Coolpix 950 digital camera produced hemispherical canopy photos with substantial color blurring towards the periphery of the exposure. We believe that chromatic aberration associated with the camera’s lens optics may be the source of this phenomenon; however, other factors may have also contributed to the diminished image sharpness. Color blur influenced (i) the size, shape, and distribution of canopy gaps; (ii) the accuracy of edge detection and the binary division of pixels into sky and canopy elements, and (iii) the magnitude, range, and replication of canopy openness, leaf area, and transmitted global radiation results. The Nikon Coolpix 950 produced canopy openness measures that were 1.4 times greater than film estimates in 22 of the 36 photo pairs. Cloud cover and sky brightness also influenced the spectral characteristics of the lateral chromatic aberration (halos), and thus had an added and unpredictable effect on canopy openness. Setting the Nikon Coolpix 950 to record in black and white, and shooting only under uniformly overcast skies will help to minimize the unpredictable effects of chromatic aberration. Nevertheless, we recommend a cautious approach when undertaking canopy measurements with the Nikon Coolpix 950, particularly when stands are dense and canopy openness falls below 10%. High-quality (1:4) JPEG compression had no significant influence on mean canopy openness; however, lower XGA and VGA image resolutions combined with 1:4 JPEG compression produced mean canopy openness results that were significantly lower than openness data extracted from uncompressed, full-resolution TIFF photos.

PHOTOGRAMMETRY OF A 5M INFLATABLE SPACE ANTENNA WITH CONSUMER-GRADE DIGITAL CAMERAS

This paper discusses photogrammetric measurements of a 5m-diameter inflatable space antenna using four Kodak DC290 (2.1 megapixel) digital cameras. The study had two objectives: 1) Determine the photogrammetric measurement precision obtained using multiple consumer-grade digital cameras and 2) Gain experience with new commercial photogrammetry software packages, specifically PhotoModeler Pro from Eos Systems, Inc. The paper covers the eight steps required using this hardware/software combination. The baseline data set contained four images of the structure taken from various viewing directions. Each image came from a separate camera. This approach simulated the situation of using multiple time-synchronized cameras, which will be required in future tests of vibrating or deploying ultra-lightweight space structures. With four images, the average measurement precision for more than 500 points on the antenna surface was less than 0.020 inches in-plane and approximately 0.050 inches out-of-plane.

Assessment of the accuracy of low-cost store-and-forward teledermatology consultation

Background: Telemedicine has the potential to revolutionize the delivery of dermatologic care to underserved areas. Objective: Our purpose was to compare diagnoses from two types of dermatology consultations: telemedicine using store-and-forward (SAF) technology, and traditional face-to-face (FTF) office visits. Methods: Skin conditions were imaged with a consumer-grade digital camera. A standardized template was used to collect historical data. Information was stored in a secured database for access by 2 or 3 board-certified dermatologists. Results from the FTF visit were used to assess the accuracy of the SAF diagnoses. Results: A total of 106 dermatologic conditions in 92 patients were included. Concordance between FTF and SAF diagnoses was high, ranging from 81% to 89% for all 3 dermatologists. Clinically relevant disagreement occurred in only 4% to 8% of cases. Remaining disagreements did not affect patient care. Diagnostic confidence and image quality affected agreement. When cases of high confidence were analyzed separately, agreement increased to 88% to 100%. This increase was substantiated by means of a chi-square test between the high confidence and low confidence groups, which demonstrated statistical significance (P < .005) for all dermatologists. Similarly, when cases of above average image quality were considered, agreement increased to 84% to 98%. Again this difference was substantiated by means of a chi-square test between adequate and poor images, with statistical significance for two dermatologists (P < .001). Accuracy was comparable between disease types with the exception of benign neoplasms, which demonstrated agreement of 22% to 46%. Conclusion: These data support the use of existing digital technology to construct an accurate SAF teledermatology system. The inexpensive camera and widely available computer equipment make this an extremely affordable system. Furthermore, participating dermatologists appear well aware of system limitations, as reflected in the increased agreement for high confidence cases. Additional investigation of the accuracy of teledermatology for benign neoplasms is warranted. (J Am Acad Dermatol 2000;42:776-83.)