2. Sharpening

2.1 Sharpening

The Sharpen tab contains all the necessary controls and sliders to control the sharpening settings. It is essential that you get these settings correct, please take the time to find the ones that are optimal for your gear setup. Besides the Telescope aperture, focal ratio, barlow lens and camera, also the seeing conditions may require a different value for the radius. 

2.1.1 Sharpening mode

The sharpening works in 2 different modes: RGB and Luminance mode.

RGB mode

RGB mode applies sharpening on the 3 channels Red, Green and Blue. This mode often results in the best color diversity, but it may introduce color noise.

Luminance mode

Luminance mode only applies sharpening to the Luminance channel. The Luminance channel  only works on the light intensity of the image while leaving the colors unchanged. The advantage of this is that sharpening will not introduce any color noise. The downside is less color richness in the image. This mode will work best on object surfaces that don't have a lot of color diversity such as the moon or the sun. 

LuckyStackWorker also provides additional checkboxes to compose the luminance channel. You can decide to drop a channel if it has more noise or a particular artifact is only visible in a certain channel. Finally you can also drop the whole color channel, effectively making the image an monochrome image.

2.1.2 Radius

Radius can be set to lower values (below 1) for lower focal distances or cameras that have large pixel sizes (5 micron), and higher values for larger focal distances or when using a camera with small pixel size. The correct value for radius thus depends on the sampling ratio of the recordings. If the image was undersampled or the sampling was spot on, it is best to keep the radius low (1 or lower). And in case the recording is oversampled it means that the radius value needs to be higher in order for the sharpening to be more effective (and introduce less noise).

2.1.3 Amount

The amount slider defines the strength of the sharpening algorithm applied. Higher values will result in better details and higher contrast, but may also bring forwards the amount of noise. The noise can be suppressed by using the Denoising controls, described in section 2.3.

2.1.4 Iterations

The number of iterations can vary based on the quality of the recording, low values (1-2) for noisy image stacks, and higher values for low noise image recordings (usually bright objects such as the moon & sun). Multiple iterations can give sharper end results and finer details, but may also increase the noise. 

2.2 Edge artifact suppression

The sliders of this menu control a custom and very effective algorithms that can be used to suppress/remove the typical bright edge artifacts that often appear near the planets horizon. There are 2 different algorithms: Dering and Clipping. Depending on the planet and other factors one might be more effective than the other. However they are both based on the same principle of applying less sharpening near the edge/horizon of the planetary surface (referred to as adaptive sharpening).

2.2.1 Deringing

Deringing is (by selecting the Dering option) is most effective on diffraction patterns. Sharpening will have the undesirable side-effect of bringing forwards such artifacts very clearly, making the end result look somewhat unnatural. By using the edge artifact suppression dering option and carefully choosing the right values for the 3 parameters strength, radius and threshold these patterns can be avoided. The Jupiter animation on the right illustrates the effect of the dering algorithm.

2.2.2 Clipping

The clipping algorithm is best used when planets edges start to become over-exposed when applying sharpening. The Mars animation on the right shows the effect of applying clipping suppression.