Slanted Knife Edge Research Articles

Influence of incident angle, anisotropy, and floating distance on aerial imaging resolution

We measure the image resolution of aerial images formed with an AIRR (aerial imaging by retro-reflection) system. Using three different types of retro-reflectors inside the AIRR system, we measure the aerial image modulation transfer function (MTF) via the slanted knife edge method, showing that the resolution of depends on the angle of incidence on the retro-reflector, the retro-reflector's anisotropy, and the aerial image's floating distance.

Aerial image resolution measurement based on the slanted knife edge method.

Image resolution is one of the most important performance specifications of aerial display techniques. However, there is no standard method for evaluating the aerial image resolution. In this paper, we propose a method for measuring the modulation transfer function (MTF) of an aerial imaging system based on the slanted knife edge method. We hypothesize that aerial images have a different blur function from standard camera images. In order to explore this, we simulate blurred slanted knife edge images by convolving two types of blur functions. Furthermore, the MTF curves of the aerial image formed using different retro-reflectors are compared using the proposed method.

Spatial resolution of novel liquid scintillating capillary array

Scintillating array image plates are allowed high resolution through a thicker detector which increases quantum efficiency without degrading the imaging resolution substantially. Due to limitations imposed by process capability, scintillator fiber array with pixel diameter less than 0.2 mm is hardly manufactured to improve performance. Therefore, a liquid scintillator capillary array with 0.1 mm pixel is developed to improve the detection efficiency and spatial resolution of image plate for low intensity radiation imaging. Its performances are studied and tested by simulation and experiment, and are compared with those of scintillating fiber array. Especially in order to gain high fidelity representation of modulation transfer function of the array image plate, a method of simulating and measuring the slanted knife edge response and an iterative algorithm are introduced. For 14 MeV neutron and 1.25 MeV gamma, the slanted knife edge responses of these array image plates with pixel dimensions in a range from 0.1 mm to 0.5 mm are respectively simulated by MCNPx program and the modulation transfer function (MTF) are obtained. The simulation results show that compared with scintillating fiber array, the liquid scintillator capillaries array has an obvious merit in spatial resolution because of greater stopping power for secondary charged particle in the capillary quartz glass wall with 0.02 mm in thickness. Its ultimate resolution can reach to 1.8 lp/mm for 14 MeV neutron by simulation. At the 4000 Ci <sup>60</sup>Co facility, a 5-cm-thick tungsten bar, one side of which has a curvature of 0.1 radian to minimize the misalignment effect, is made a knife edge. The MTF of the scintillating fiber array with 0.3 mm and 0.5 mm pixel and newly developed liquid scintillator capillary array is measured through this tungsten knife edge. Experimental measurement results have also verified that the liquid scintillator capillary array performs well in spatial resolution and luminescent uniformity for 1.25 MeV gamma. The ultimate spatial resolution, 0.9 lp/mm is gained, and those of other scintillating fiber arrays are all less than 0.5 lp/mm. Moreover, experimental test validates the simulating method and simulated results, although the measured value is slight less than the simulated value because of the effect of dimension of <sup>60</sup>Co source.

Evaluation of Image Resolution of Aerial Image Based on Slanted Knife Edge Method

Evaluation of Image Resolution of Aerial Image Based on Slanted Knife Edge Method

Evaluation of Image Resolution of Aerial Image Based on Slanted Knife Edge Method

Evaluation of Image Resolution of Aerial Image Based on Slanted Knife Edge Method

Modified slanted-edge method to measure the modulation transfer function of camera

The slanted-edge method specified in ISO Standard 12223, which experiences large errors in the camera modulation transfer function(MTF) due to tilt angle error in the knife-edge resulting in non-uniform sampling of the edge spread function. In order to resolve this problem, a modified slanted-edge method for camera MTF measurement is proposed. By applying a simple direct calculation of the Fourier transform of the derivative for the non-uniform sampling data, the camera super-sampled MTF results are obtained. Theoretical simulations for images with and without noise under different tilt angle errors are run using the proposed method. It is demonstrated that the MTF results are insensitive to tilt angle errors. To verify the accuracy of the proposed method, an experimental setup for camera MTF measurement is established. Measurement results show that the proposed method is superior to traditional methods, and improves the universality of the slanted knife-edge method for camera MTF measurement.

A method to measure the modulation transfer function of Bayer filter color camera

With the development of optoelectronic technologies, color cameras have been widely exploited in space remote sensing, earth observations from space, environmental monitoring, urban construction, and many other fields. Currently, most commercial color cameras use a single charge coupled device (CCD) or complementary metal-oxide-semiconductor (CMOS) sensor that has a Bayer color filter array (CFA) on its pixel surface to obtain red (R), green (G), or blue (B) samples. As a way of evaluating imaging quality, modulation transfer function (MTF) can provide a comprehensive and objective metric for camera imaging performance. In the conventional knife-edge method for color camera MTF measurement, a linear uniform sampling of the edge spread function (ESF) must be completed before a fast Fourier transform (FFT) can be applied. As the sampling rate becomes large, the number of pixel points on the line which is parallel to the knife-edge become less. So taking average of the pixel points to obtain ESF can be strongly affected by the noise of sensor. Therefore it is necessary to balance the influences of sampling rate and sensor noise on the MTF measurement, and the recommended sampling rate is 4-6. When the tilt angle of knife-edge has an error, the non-uniform sampling ESF can be obtained by the slanted knife-edge method. This leads to a variation in the results of the camera MTF on a spatial frequency scale and early cut-off. The best MTF results of camera can be obtained by rotating knife-edge, calculating MTF power under different tilt angles of knife-edge, and finding the maximum MTF power. And we propose an algorithm for Bayer filter color camera MTF measurement. The algorithm processing includes extracting R, G, B colors of knife-edge images; projection; differential operation; Hanning window filtration; FFT; correction; weighting combination of R, G, B colors MTF; MTF power calculation; optimal tilt angle of knife-edge estimation. To verify the accuracy of the proposed method, the weighting response factors of R, G, B colors are calibrated and an experimental setup for color camera MTF measurement is established. The knife-edge target is rotated in angle steps of 0.02, and the MTF results are calculated under different tilt angles of knife-edge within0.1 surrounding the estimate position by the proposed algorithm. The maximum differences of MTF results between the proposed method and fringe target method are 0.061 (Nyquist frequency fc) and 0.043 (fc/2), respectively. The results show that by searching the optimal tilt angle of knife-edge, the effect of non-uniform sampling on MTF result of color camera can be eliminated. Compared with the conventional method, the proposed method is superior for the measurement of the super-sampled MTF of color camera. Meanwhile, this method can also be applied to MTF measurements of radiographic systems, such as X-ray imaging system and other systems.

Modified slanted-edge method and multidirectional modulation transfer function estimation

The slanted-edge method specified in ISO Standard 12233, which measures the modulation transfer function (MTF) by analyzing an image of a slightly slanted knife-edge target, is not robust against noise because it takes the derivative of each data line in the edge-angle estimation. We propose here a modified method that estimates the edge angle by fitting a two-dimensional function to the image data. The method has a higher accuracy, precision, and robustness against noise than the ISO 12233 method and is applicable to any arbitrary pixel array, enabling a multidirectional MTF estimate in a single measurement of a starburst image.