The function called "Pixel Offset Live" has been renamed "Spectral Analyser".
The "Save protus" feature was added since the Protus image looks better with the transversalium turned off, while the Clahe image looks better with it turned on.
"Stubborn transversalium" can be used for very intense line defects. Since it can also cause artefacts, this function should be used sparingly (for example, to rescue data that otherwise would be spoiled). Ideally, it is better to try to clean dust off the slit so that a low setting of the normal transversalium correction is sufficient.
"Ellipse fit shift" does not normally need to be changed from the default value of 10 pixels. But if the dispersion is very high (for example, if using a higher power diffraction grating like 3600 l/mm) then a larger pixel shift is required to move the same wavelength distance. A value of 20 then will help the program with its edge detection, which is necessary to do ellipse fit.
The "de-vignette" function is a very useful new feature that attempts to equalise the brightness along the slit. For a number of reasons (typically optical misalignment or an obstructed light path), there can be either unequal darkening on the ends of the slit or there can be excessive darkening on both sides. This function tries to match the limb darkening along the slit with that perpendicular to the slit.
Below are two examples of "de-vignette". The first shows a mild darkening on the right side (the scan in vertical). The second shows a very strong vignetting on both ends of the slit, with the right side much darker. The "de-vignette" does an acceptable job of correcting even the very strong case, although ideally the source of the vignetting should be addressed.
"De-vignette" can potentially lead to excessive brightness at the edges of the sun and possibly also some slight brightness banding.
- Example of a mild vignetting. Left: uncorrected. Right: with de-vignette.
- 092940_H-alpha_de-vignette.jpg (267.26 KiB) Viewed 1096 times
- Example of very strong vignetting. Left: uncorrected -- data almost unusable. Right: with de-vignette -- image passable.
- 075945_H-alpha_de-vignette.jpg (361.9 KiB) Viewed 1096 times
