Comparison of MTF measurements using edge method: towards reference data set

Abstract

A sensor's spatial resolution has traditionally been a difficult concept to define, but all would agree that it is inextricably linked to the Ground Sampling Distance (GSD) and Instantaneous Field of View (IFOV) of an imaging sensor system. As a measure of the geospatial quality of imagery, the Modulation Transfer Function (MTF) of the system is often used along with the signal-to-noise ratio (SNR). However, their calculation is not fully standardized. Further, consistent measurements and comparisons are often hard to obtain. Therefore, in the Infrared and Visible Optical Sensors (IVOS) subgroup of the Working Group on Calibration Validation (WGCV) of the Committee for Earth Observation Satellites (CEOS), a team from various countries and professional entities who are involved in MTF measurement was established to address the issue of on-orbit MTF measurements and comparisons. As a first step, a blind comparison of MTF measurements based on the slanted edge approach has been undertaken. A set of both artificial and actual satellite edge images was developed and a first comparison of processing results was generated. In all, seven organizations contributed to the experiment and several significant results were generated in 2016. No single participant produced the best results for all test images as measured by either the closest to the mean result, or closest to the truth for the synthetic test images. In addition, close estimates of the MTF value at Nyquist did not ensure the accuracy of other MTF values at other spatial frequencies. Some algorithm results showed that the accuracy of their estimates depended upon the type of MTF curve that was being analyzed. After the initial analysis, participants were allowed to modify their methodology and reprocess the test images since, in several cases, the results contained errors. Results from the second iteration, in 2017, verified that the anomalies in the experiment's first iteration were due to errors in either coding or methodology, or both. One organization implemented a third trial to fix software errors. This emphasizes the importance of fully understanding both methodology and implementation, in order to ensure accurate and repeatable results. To extend this comparison study, a reference data set, which is composed of edge images and corresponding MTF curves, will be built. A broader audience will be able to access the edge images through the CEOS CalVal Portal (http://calvalportal.ceos.org/. This paper, which is associated with the reference data set, can serve as a new tool to either implement or check, or both, the MTF measurement that relies on the slanted edge method.

Radiometric Quality Assessment for Maxar Hd Imagery

“…The MTF values were evaluated at the Nyquist frequency, and found consistent in the AC directions. The RER is the slope of the ESF and the SNR is the ratio of the edge height to the mean standard deviations of on either side of the ESF curve(Viallefont- Robinet et al, 2018). The results obtained here are again consistent in both AL and AC directions, although again indicate blurring effect by the ESF and RER values.…”

“…A classical slanted-edge (i.e. knife-edge) method was applied (Viallefont-Robinet et al, 2018;Kohm, 2004;Crespi and Vendictis, 2009). The implementation of the slanted-edge method has four steps, i.e.…”

“…The implementation of the slanted-edge method has four steps, i.e. edge identification and orientation, edge modeling, ESF construction, and MTF computation from the ESF (Viallefont-Robinet et al, 2018). The slanted-edge method used in the study was inspired from the method of Kohm (2004).…”

Design Considerations for Discrete Frequency Infrared Microscopy Systems

“…215 But the accuracy of the MTF estimates is highly dependent on the acquired image edge contrast, the noise levels (S/N) and the edge orientation angle with respect to the horizontal and vertical directions. For systems showing asymmetrical defects, the sagittal and meridional MTFs show a considerable difference and they can be separately estimated instantaneously [214][215][216] using commercial targets. By capturing edges at consecutive different slant angles, this method can also be extended to reconstruct an approximate 2D MTF and by applying the inverse Radon transform, 217 the full 2D PSF.…”

Calibration of programmable spectral imager with dual disperser architecture

“…The modulation transfer function (MTF) of the system was determined via the slanted edge method [28], with results shown in Figure 23. Given a pixel size of 5.5 µm, the system has a resolution of 11 µm (defined as the visibility of 21% at the half the Nyquist frequency).…”