Walter L. Snow

Calibration of CCD cameras for field and frame capture modes

Small format, medium resolution CCD cameras are at present widely used for industrial metrology applications because they are readily available and relatively inexpensive. The calibration of CCD cameras is necessary in order to characterize the geometry of the sensors and lenses. In cases where a static or slowly moving object is to be imaged, frame capture mode is most often used to maximize the resolution of the CCD sensor. In cases where the object to be imaged is in rapid motion, field mode capture is frequently adopted to avoid discontinuities caused by the interlaced scanning process used by the sensors. A strategy for the computation of calibration parameters for field modes, based on a frame mode calibration, is proposed. The strategy is then verified by testing using real data from test range calibrations of three different types of CCD camera. The results of these calibration tests are described, with particular emphasis on the changes required to adjust between frame and field capture modes.

The spectral opacity of triatomic carbon measured in a graphite tube furnace over the 280 to 600 nm wavelength range

The opacity of linear triatomic carbon (C3) was measured in a graphite tube furnace from 280 to 600 nm to supplement the earlier measurement of Brewer and Engelke. Data are presented for a maximum centerline temperature range of 2720–3060 K.

Rigid body motion analysis system for off-line processing of time-coded video sequences

Photogrammetry affords the only noncontact means of providing unambiguous six-degree-of- freedom estimates for rigid body motion analysis. Video technology enables convenient off- the-shelf capability for obtaining and storing image data at frame (30 Hz) or field (60 Hz) rates. Videometry combines these technologies with frame capture capability accessible to PCs to allow unavailable measurements critical to the study of rigid body dynamics. To effectively utilize this capability, however, some means of editing, post processing, and sorting substantial amounts of time coded video data is required. This paper discusses a prototype motion analysis system built around PC and video disk technology, which is proving useful in exploring applications of these concepts to rigid body tracking and deformation analysis. Calibration issues and user interactive software development associated with this project will be discussed, as will examples of measurement projects and data reduction.

Influence of storage media on the accuracy and repeatability of photogrammetric measurements using CCD cameras

A clear advantage of digital photogrammetric measurement over other, more conventional techniques in the fast sample rate of the data acquisition. CCD cameras and video systems can be used very effectively to analyze dynamic objects or cases of rapid deformation. However, long sequences of images can introduce the penalty of large volumes of digital data, which may not be able or appropriate to be processed in real time. The images are typically stored in analog form, using media such as video tape or video disk, for off line processing subsequent to the image capture. This paper investigates the degradation in accuracy and repeatability caused by the influence of the analog recording. A number of experiments using a Hitachi medium resolution CCD camera, a three dimensional test range and a self calibrating bundle adjustment are described. For cases of near real time monitoring, the ability of frame averaging to reduce the degradation caused by the analog recording is also investigated. The results of the experiments are presented in summary to provide some guidelines as to the degree of degradation which can be expected under similar circumstances.