| 摘要 |
Video cameras, such as charge coupled device cameras, are used for optically making dimensional measurements of laser beams. Such cameras have drawbacks including baseline offset error, shading error, pixel-to-pixel fixed pattern offsets, and poor signal-to-noise ratio. Methods and apparatus to correct for these errors, without losing any desired signal components, wherein the baseline offset error is corrected without the loss of any signal components that may otherwise be obscured due to noise. The baseline of the signal is raised above a digitizer's zero level, an average baseline without an input signal present is determined, and then the average baseline is subtracted from the subsequently obtained signals. The subtraction process is performed such that the subsequent frames in memory retain all negative signal components, as well as positive signal components, and thus there is no loss of the desired signal. Any subsequent quantitative measurements consider both the positive and negative signal components and thus measurements are made as accurately as possible. After the baseline error is corrected, one or more of a number of noise reduction methods are implemented to improve the signal-to-noise ratio. |
