Interferometric microscope with true color imaging
Optical 3D profilers based on Coherence Scanning Interferometry (CSI) provide high-resolution non-contact metrology for a broad range of applications. Capture of true color information together with 3D topography enables the detection of defects, blemishes or discolorations that are not as easily identified in topography data alone. Uses for true color 3D imaging include image segmentation, detection of dissimilar materials and edge enhancement. This paper discusses the pros and cons of color capture using standard color detectors and presents an alternative solution that does not rely on color filters at the camera, thus preserving the high lateral and vertical resolution of CSI instruments.
Resolution for color photography
Although it is well known that luminance resolution is most important, the ability to accurately render colored details, color textures, and colored fabrics cannot be overlooked. This includes the ability to accurately render single-pixel color details as well as avoiding color aliasing. All consumer digital cameras on the market today record in color and the scenes people are photographing are usually color. Yet almost all resolution measurements made on color cameras are done using a black and white target. In this paper we present several methods for measuring and quantifying color resolution. The first method, detailed in a previous publication, uses a slanted-edge target of two colored surfaces in place of the standard black and white edge pattern. The second method employs the standard black and white targets recommended in the ISO standard, but records these onto the camera through colored filters thus giving modulation between black and one particular color component; red, green, and blue color separation filters are used in this study. The third method, conducted at Stiftung Warentest, an independent consumer organization of Germany, uses a whitelight interferometer to generate fringe pattern targets of varying color and spatial frequency.
Calibration of high-speed optical profiler
Optical profilers that employ white-light interferometry (WLI) techniques are widely used in industry and research to map surface structures with precise sub-nanometer resolution. The accuracy, repeatability and consistency of these instruments depend mainly on the proper calibration of two parameters: the mean wavelength and the scanner speed. Equally important in industrial applications is high throughput of measuring devices; high throughput can be achieved by increasing the speed of the measurement, which in turn reduces the sampling rate of the interference signal. Again, exact calibration of the system is the key to obtaining accurate measurements. Our solution for calibrating the system involves inserting into the optical profiler a second, laser-based, reference signal interferometer that creates a primary length standard for calibration. This innovation allows for substantially improved performance and repeatability at different measurement speeds up to 100 microns per second and over an 8 millimeter scanning range.