Wavelet Sharpening

The Wavelet filter in RegiStax is controlled by six sliders and three settings. From 1 to 6, the sliders affect detail at lower spatial frequencies, corresponding to features of larger angular size. The first two settings are located above the sliders. Initial Layer raises or lowers the Wavelet filter’s highest frequency. Step Increment increases or decreases the range of frequencies. The final setting is located at the top of the screen, titled Wavelet. When you click this tab, a window with a grid of numbers appears, displaying the setting of the filter itself. By raising the central number, I can achieve better results than with the default setting of 50. Like all my other decisions, this will be dictated by the quality of my stacked image; if the movie was recorded under outstanding conditions, I may start by raising the center frequency to 1,200, and then see how this affects my image by raising the first slider. Lower numbers translate into lower frequencies and smaller steps between the 6 layers (4).

When I’m comfortable with all these settings, I move the slider of the first wavelet layer as far as possible to the right before noise becomes objectionable. Then I move on to the second and perhaps the third wavelet, until I’m satisfied with the results. I only use the lower frequencies when the seeing is particularly poor, or if my target was very small, such as Uranus, Neptune, or perhaps Mars far from opposition. During these steps I use the Gamma and Histogram functions to enhance contrast, avoiding clipping the high pixel values. I find the Brightness and Contrast functions tend to clip the brightest and darkest areas of the image, so I avoid using them (5). Finally, I save the sharpened result as a 16-bit TIFF file.