Enhancing Coronal Structures With the Fourier Normalizing-Radial-Graded Filter

Abstract

Images of the corona have a high dynamic range which is excellent for quantitative photometric analysis. To understand the processes governing the solar corona, it is essential to have information about the absolute brightness as well as the underlying structure. However, due to the steep radial gradient of brightness in the images, and to the fact that structures closer to the solar disk have higher contrast than structures further from the disk, human vision cannot view the intricate structure of the corona in such images. The recently developed normalizing-radial-graded filter (NRGF) is an effective way for revealing the coronal structure. In this work, we present a more adaptive filter inspired by the NRGF, which we call the Fourier normalizing-radial-graded filter (FNRGF). It approximates the local average and the local standard deviation by a finite Fourier series. This method enables the enhancement of finer details, especially in regions of lower contrast. We also show how the influence of additive noise is reduced by a modification to the FNRGF. To illustrate the power of the method, the FNRGF is applied to images of emission from coronal forbidden lines observed during the 2010 July 11 total solar eclipse. It is also successfully applied to space-based observations of the low corona in the extreme ultraviolet and to white light coronagraph observations, thus demonstrating the validity of the FNRGF as a new tool that will help the interpretation of the information embedded in most types of coronal images.

Tracking CMEs using data from the Solar Stormwatch project; observing deflections and other properties

“…The analysis was limited by restrictions in average household internet bandwidth at the time the project was instigated. Improvements could now be made with faster internet speeds and advances in image processing techniques [ Druckmullerova et al , ], [ DeForest et al , ].…”

“…The analysis was limited by restrictions in average household internet bandwidth at the time the project was instigated. Improvements could now be made with faster internet speeds and advances in image processing techniques [Druckmullerova et al, 2011], [DeForest et al, 2011]. (top left) Participants first marked the appearance time, the time the CME reached the blue circle, and the position angle and width of the CME in the COR2 field of view.…”

Structure and Dynamics of the 2012 November 13/14 Eclipse White-Light Corona

“…Though manual, our reduction method was similar to that used by Druckmüller et al (2006Druckmüller et al ( , 2014, Druckmüller (2009), andDruckmüllerová et al (2011). Druckmüller's system was unable to handle the REDCODE RAW format of our RED Epic images.…”

Multi-Scale Gaussian Normalization for Solar Image Processing

“…The technique is computationally expensive but gives very good results. A less sophisticated, yet very efficient technique to reveal features above the limb is based on techniques originally developed for coronagraphs (Morgan, Habbal, and Woo, 2006;Druckmüllerová, Morgan, and Habbal, 2011). Most relevant to this work is the recently developed Noise Adaptive Fuzzy Equalization (NAFE) method (Druckmüller, 2013).…”