The Mask feature is an integral part of StarTools. Many modules use a mask to operate on specific pixels and parts of the image, leaving other parts intact.
Importantly, besides operating only on certain parts of the image, it allows the many modules in StarTools to perform much more sophisticated operations.
You may have noticed that when you launch a module that is able to apply a mask, the pixels that are set in the mask will flash three times in green. This is to remind you which parts of the image will be affected by the module and which are not. If you just loaded an image, all pixels in the whole image will be set in the mask, so every pixel will be processed by default. In this case, when you launch a module that is able to apply a mask, the whole image will flash in green three times.
You may have noticed that when you launch a module that is able to apply a mask, the pixels that are set in the mask will flash three times in green.
Green coloured pixels in the mask are considered 'on'. That is to say, they will be altered/used by whatever processing is carried out by the module you chose. 'Off' pixels (shown in their original colour) will not be altered or used by the active module. Again, please note that, by default all pixels in the whole image are marked 'on' (they will all appear green).
For example, an 'on' pixel (green coloured) in the Sharp module will be sharpened, in the Wipe module it will be sampled for gradient modelling, in Synth it will be scanned for being part of a star, in Heal in will be removed and healed, in Layer it will be layered on top of the background image, etc.
The Mask Editor is accessible from the main screen, as well as from the different modules that are able to apply a mask. The button to launch the Mask Editor is labelled 'Mask'. When launching the Mask Editor from a module, pressing the 'Keep' or 'Cancel' buttons will return StarTools to the module you pressed the 'Mask' button in.
As with the different modules in StarTools, the 'Keep' and 'Cancel' buttons work as expected; 'Keep' will keep the edited Mask and return, while 'Cancel' will revert to the Mask as it was before it was edited and return.
As indicated by the 'Click on the image to edit mask' message below the image, clicking on the image will allow you create or modify a Mask. What actually happens when you click the image, depends on the selected 'Brush mode'. While some of the 'Brush modes' seem complex in their workings, they are quite intuitive to use.
Apart from different brush modes to set/unset pixels in the mask, various other functions exist to make editing and creating a Mask even easier;
NOTE: To quickly turn on all pixels, click the 'clear' button, then the 'invert' button.
Different 'Brush modes' help in quickly selecting (and de-selecting) features in the image.
For example, while in 'Flood fill lighter pixels' mode, try clicking next to a bright star or feature to select it. Click anywhere on a clump of 'on' (green) pixels, to toggle the whole clump off again.
The mask editor has 10 'Brush modes';
The powerful 'Auto' function quickly and autonomously isolates features of interest such as stars, noise, hot or dead pixels, etc.
For example, isolating just the stars in an image is a necessity for obtaining any useful results from the 'Decon' and 'Magic' module.
The type of features to be isolated are controlled by the 'Selection Mode' parameter
Some of the selection algorithms are controlled by additional parameters;
Finally, the 'Source' parameter selects the source data the Auto mask generator should use. Thanks to StarTools' Tracking functionality which gives every module the capability to go "back in time", the Auto mask generator can use either the original 'Linear' data (perfect for getting at the brightest star cores), the data as you see it right now ('Stretched'), or the data as you see now but taking into account noise propagation ('Stretched (Tracked)'). The latter greatly helps reduce false positives caused by noise.
StarTools stores the masks you used in your workflow in the StarTools.log file itself. This StarTools.log file is located in the same folder as the executables. The masks are encoded as BASE64 PNG images. To convert the BASE64 text into loadable PNG images, you can use any online (or offline) BASE64 converter tool.
The part to copy and paste, typically starts with;
One online tool for BASE64 is Motobit Software's BASE64 encoder/decoder.
To use it to convert StarTools masks back into importable PNG files;
This should result in a download of the mask as a PNG file which can be imported into the StarTools mask editor, as welll as other applications.
The mask editor and its auto-mask generator are very flexible tools. These more advanced techniques will allow you to create specialised masks for specific situations and purposes.
Sometimes, it is desirable to keep an object or area from being included in an auto-generated mask. It is possible to have the auto-mask generator operate only on designated areas;
Where documentary photography is concerned, selective manipulation by hand is typically frowned upon, unless the practice of it is clearly stated when the final result is presented.
However, in cases where a mask is algorithmically derived, purely from the dataset itself, without adding any outside extra information, masking is common practice even in the realm of documentary photography. Examples of such use cases are range masks (for example, selecting highlights only based on brightness), star mask (selecting stars only based on stellar profile), colour masks (selecting features based on colour), etc.
In some modules in StarTools specifically, masks are used for the purpose of selective sampling to create internal parameters for an operation that is applied globally to all pixels. This too is common practice in the realm of documentary photography. Examples of such use cases are gradient modelling (selecting samples to model a global gradient on) and color balancing (selecting samples to base an global white balance on).
Finally, it is also generally permitted to mask out singularities (pixels with a value that is unknown) by hand, in order to exclude this from some operations that may otherwise generate artefacts in response to encountering these. Examples may be over-exposing star cores, dead or hot pixels, stacking artefacts, or other data defects.
As a courtesy, when in doubt, it is always good to let you viewers know how you processed an image, in order to avoid confusion.
By tracking signal and noise evolution during processing, it lets you effortlessly accomplish hitherto "impossible" feats.
Open an image stack ("dataset"), fresh from a stacker.
The noise signature of the deliberately left-in noise, is precisely shaped to be aesthetically pleasing for precisely this purpose.
The Filter module allows for the modification of features in the image by their colour by simply clicking on them.
You can convert everything you see to a format you find convenient. Give it a try!