Using Previews to Try Out Processes
We'll elaborate thoroughly on this and other related topics in documentation chapters dedicated to processes and processing windows. Here we offer you just a brief introduction so that you can figure out how a preview object can be used to essay processes in PixInsight.
In general, you can apply a process to a preview just as you'd apply it to an image view. As for the way a process works with pixel data, there is no functional difference between image views and previews. Of course, we are referring to processes that can be previewed, as CurvesTransform or SGBNR, for example; there are processes that cannot be applied to previews, as geometrical processes like Resample, for example.
As we've said, you'll find a detailed discussion on this topic in chapters dedicated to processes, so let's put just an easy example to help you understand basic concepts. Consider the following image window. The image is a lunar mosaic generated in PixInsight Standard Edition. There are three previews defined over areas of particular interest.
Now suppose we want to play a little with wavelets processing in PixInsight LE. The first release of PixInsight LE (version 1.0.0) included a strongly limited set of tools for wavelets processing, mainly focused on small-scale noise reduction. Starting with version 1.0.1, PixInsight LE includes the full ATrousWaveletTransform process, just as implemented in PixInsight Standard as of the date of release.
ATrousWaveletTransform is an extremely powerful and flexible process to perform both tasks of image restoration and noise reduction. When properly applied to high-resolution CCD lunar and planetary images, ATrousWaveletTransform yields outstanding results.
The standard interface for the ATrousWaveletTransform process is the À Trous Wavelets window. To open and activate it, click the corresponding tool button on the Advanced Processing tool bar, or use the main menu option.
Using Process Drag Objects
Now we enter appropriate parameters, according to the task we want to accomplish. In the example shown on the figure above, our intention is to enhance image structures at small dimensional scales. This is usually the case when working with lunar images. The smallest scale (first wavelet layer) includes both significant structures and some high-frequency noise; hence noise reduction parameters have been used. The same happens with the second wavelet layer. Of course we'll include a detailed description of the À Trous Wavelets window in this documentation; this is just a quick-and-dirty example.
Once we are done defining what we consider a good set of parameters, let's use a preview to try it out. On each processing window in PixInsight, a small square object is located near the window's bottom left corner, which is called a process drag object. Process drag objects play a key role in PixInsight's object-oriented interface, and in fact these small things confer PixInsight much of its character, as you'll understand well when you get accustomed to them.
Now we click on the process drag object, drag it, and place it over the view selector corresponding to Preview01. The green line on the figure below shows you how to move the mouse without releasing the left button:
As soon as the process drag object is placed over its corresponding view selector, Preview01 is selected as the window's current view. However, we cannot apply a process to a view selector, as indicated by the x-shaped cursor that can be seen above. When we move the mouse to the right, on the preview's subimage, we can see how the cursor changes its shape to tell us that now it's OK to apply the process to the view under the mouse cursor:
Finally, when we drop the process drag object by releasing the mouse button, this is what happens after a few seconds of processing time:
Of course, dragging a process drag object over a view selector is only required if the window's current view is not the view we want to try a process in. Otherwise, we can just drag the process object and drop it on the image.
Using a Set of Previews with Standard Preview Buttons
What about testing the ATrousWaveletTransform on the three previews defined in our example? Do we have to drag and drop the process drag object three times, each time we want to preview? Of course we don't. On processing windows that are interfaces to previewable processes, two buttons can be found near the window's bottom right corner, namely the Preview and Select Preview List buttons. These buttons are known as the standard preview buttons of processing windows. The Select Preview List button is a small square button with a down arrow.
If you click the Select Preview List button, the Preview Selection Dialog appears, where you can select one or more previews among all the currently defined previews, including all the images currently open.
As processing time is a linear function of the number of pixels for most processes, the information given is relevant in terms of the time you may expect to have to wait for the preview operation to complete. When you are done, press the OK button, and then click the Preview button. The process will be applied sequentially to all the selected previews.
The list of selected previews is remembered and will be used as long as the selected previews are not destroyed and the list is not changed. A similar system exists for images, and is accessible through the Apply and Select Image List buttons, known as the standard apply buttons. Each processing window maintains its own lists of selected previews and images. Further details on this system of multiple preview and image selection will be given in chapters dedicated to processes and processing windows.
Using Undo/Redo Preview to Verify Changes
To complete this brief tour on how to use previews, let us just mention that you can use the Undo/Redo Preview function in order to quickly change between the original and processed preview subimages. To invoke this function, you may use the corresponding keyboard shortcut, Shift-Ctrl-Z, the associated tool button, as shown below, or themain menu option. This option works just like the normal Undo/Redo does for images.
Note that a hint window is shown when you pass the mouse cursor over the undo preview tool button, which informs you about the process that can be undone or redone, if one exists for the current (or selected) preview in the active image window.