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Imaging Systems
Published in Araz Yacoubian, Optics Essentials, 2018
MTF measures of the spatial frequency response of the imaging system. Typically a test pattern is used to measure MTF, such as the 1951 USAF target or any appropriate resolution target. Choice of correct resolution target is key to testing the characterizing the MTF of the optical system. An example of the MTF test procedure is to capture an image of the resolution test pattern with the optical imaging system under test, and calculate MTF versus spatial frequency (typically given in line pairs per millimeter [lp/mm] or dots per inch). Some of the fine lines in the resolution test pattern will not be resolved, namely, multiple thin lines will appear to be fused together, indicating the resolution limit of the optical system. This will be apparent in the MTF graph, where MTF reaches zero beyond spatial frequencies where the system could resolve lines.
Optics in Digital Still Cameras
Published in Junichi Nakamura, Image Sensors and Signal Processing for Digital Still Cameras, 2017
Modulation transfer function (MTF) is frequently used as a standard for evaluating the imaging performance of any lens, not merely those used in DSCs. MTF is a transfer function for spatial frequency and is one of the measures used to show how faithfully object patterns are transferred to the image. The graph in Figure 2.5 shows an example of MTF spatial frequency characteristics, with the vertical axis showing the MTF as a percentage and the horizontal axis showing the spatial frequency (line-pairs/mm). The unit for the horizontal axis shows the number of stripes of light and dark (line-pairs) photographed per millimeter in the image plane. The graph normally shows a line falling away to the right as it does in the figure because the higher the frequency (the more detailed the object pattern), the greater the decline in object reproducibility. These graphs are best seen as a gauge for reproducing contrast through a range from object areas with coarse patterning to areas with fine patterning. The term “resolution” has also often been used in this context. This is a measure for evaluating the level of detail that can be captured, and line-pairs/mm is also widely used as a unit of resolution.
Visual Inspection of Tissues with Certain Endoscopes and Other Optical Devices
Published in Robert B. Northrop, Non-Invasive Instrumentation and Measurement in Medical Diagnosis, 2017
An important figure of merit for any imaging system is its modulation transfer function (MTF), S(u), also called its contrast transfer function. The MTF concept can be applied to any component of, or an entire imaging system; x-ray systems, endoscopes, CCD cameras, film, etc. can all be characterized by an MTF. The MTF is a normalized spatial sinusoidal frequency response comparing the amplitude response of the image to a spatial sinusoidal (+dc) object. In the x-dimension, the object's sinusoidal intensity is given by I(x)=(Io/2)[1+cos(2πux)],where the maximum intensity is Io and u is the spatial frequency in cycles/mm.
Performance evaluation of dual-layer architectures for high dynamic range head mounted displays
Published in Journal of Information Display, 2023
The system performance is evaluated by three factors: modulation effectiveness, image sharpness and pupil stability. The modulation effectiveness determines the image authenticity, which we use the root mean square error (RMSE) between the illuminance of the reconstructed image and original image as an evaluation factor. To consider the human eye perceptions, the JND map and the noticeable luminance error percentage are also considered as evaluation factors to evaluate the image reconstruction differences and errors. MTF is used to quantify the reconstructed image sharpness, which is the capability of recovering image content in different spatial frequencies. The slanted edge method is used to test the system MTF in the experiment. Pupil stability is evaluated by the reconstruction error variation as the viewing position moves within the eyebox. By moving the camera position within the eyebox and calculating the RMSE and JND percentage changes of the reconstructed image, we can determine the pupil stability at different pupil positions.
Comprehensive Data Set of Single Particle Combustion under Oxy-fuel Conditions, Part I: Measurement Technique
Published in Combustion Science and Technology, 2021
Nikita Vorobiev, Sarah Valentiner, Martin Schiemann, Viktor Scherer
The optical resolution was determined using a test target USAF 1951 and by the slanted-edge method, which delivers the point spread function (PSF) and the modulation transfer function (MTF) of the system (de Ruijter and Weiss 1992). The PSF describes the degradation of a point light source by the optical system. This information is transferred into the frequency domain and is represented by the MTF as contrast decay over increasing spatial frequency. The optical resolution of the long-distance microscope is about 6 µm, calculated from the Rayleigh criterion based on the numerical aperture given by the manufacturer at 600 mm working distance and for λ = 550 nm. However, this value is further limited in the optical path by the image intensifier, whose resolution is 32 line pairs per millimeter (15.6 µm). The overall resolution is slightly increased by magnification, such that at least the fourth element of the fifth group of the USAF 1951 target cannot be resolved. This corresponds to an optical resolution between 12.4 and 11.05 µm. The overall optical resolution obtained by analysis of slanted-edge images at different distances to the focus plane is shown in Figure 2 and fits well with the measurement of the USAF-1951-target. For the evaluation of the resolution limit, the 5%-contrast value of the MTF was assumed and the value applies only for the relevant part of the field of view.
Print clarity on digitally printed textiles – a quantitative evaluation
Published in The Journal of The Textile Institute, 2020
Xingyu Li, Nancy B. Powell, Stephen Michielsen
The MTF is used to illustrate radiographic sharpness, and is a measurement of the contrast reduction, or blurring, imposed by the system as a function of spatial frequency. It is more convenient to measure the response to discrete functions for radiographic imaging, such as bar patterns and square waves. The response to a square wave as a function of frequency or wavelength is referred to as the Contrast Transfer Function (CTF). It is a function that relates how a bar pattern is transferred to an imaging system as a function of the dimensions of the bars (Pawlak, 2002). In this research, the CTF was determined experimentally for a test pattern, which was used for the quantitative evaluation of print clarity on paper or textile substrate. Contrast of image, Cimage, which characterizes the print clarity of gap-bar-gap set test pattern, was compared for different conditions.