The HDR (High Dynamic Range) module optimises local dynamic range, in order to bring out the maximum amount of detail that is hidden in your data.
A HDR optimisation tool is a virtual necessity in astrophotography, owing to the huge brightness differences (aka 'dynamic range') innate to various objects that exist in deep space.
The HDR (High Dynamic Range) module optimises local dynamic range, in order to bring out the maximum amount of detail that is hidden in your data.
As opposed to other approaches (for example wavelet-based ones), the HDR module enhances dynamic range allocation locally (not just globally). It further takes into account psycho-visual theory (i.e. the way human vision perceives and processes detail) in the way the controls operate on the image.
Finally, the HDR module does not exacerbate noise grain like simpler dynamic range algorithms, factoring in noise propagation into the size of the final detail enhancement.
The result is an artefact free, totally natural looking image with real detail that does not suffer from the problems that other approaches suffer from, such as looking 'flat', looking too busy, or blowing out highlights such as stars.
The HDR module optimises local dynamic range allocation for smaller details (e.g. on a more local level) than the Contrast module; the HDR module works primarily medium-to-small features in the image.
The HDR module complements the Sharpen module and is generally a more flexible and powerful alternative that generally achieves artifact-free results. Examples of use cases are bright galaxy cores where small detail is still recoverable in the highlights.
The HDR module does not exacerbate noise grain like simpler dynamic range algorithms, factoring in noise propagation into the size of the final detail enhancement. As such, it is meant after your non-linear dataset has been stretched, for example using the Development or AutoDev modules.
As with most modules in StarTools, the HDR module comes with a number of presets;
Going beyond the presets, more detailed adjustments can be made, starting with the 'Detail Size Range' parameter. This parameter is highly influential on the end result. It governs the range of detail sizes HDR should concentrate on, in order to bring out the most detail. Keeping this value small will see small detail accentuated. However, using larger values will see both small and large structural detail modified. Using larger values will progressively dig out larger scale structures and can be quite effective in highlighting these.
A selection of different algorithms to bring out detail exists. These are chosen through the 'Algorithm' parameter;
In order to throttle how much the shadows and highlights respond to the enhancements, a brightness mask is used, the power of which is controlled by the 'Dark/Bright Response' parameter.
I'm relatively new to image processing and just wanted to say how straight forward and powerful StarTools is.
The 'Red, Green and Blue Increase/Reduce' parameters are the most important settings in the Color module.
Noise grain caused by shot noise (aka Poisson noise) - the bulk of the noise astrophotographers deal with - exists on all size levels, becoming less noticeable as the size increases.
The noise signature of the deliberately left-in noise, is precisely shaped to be aesthetically pleasing for precisely this purpose.
You can convert everything you see to a format you find convenient. Give it a try!