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A new screen can be created from File→New Image or using 
button in the top toolbar. If command is executed from File→ New, application opens a Window for setting width, height, background color of the screen image to be created.
By default, width and height are derived from the current application main window display area to make sure created screen image fits in the display area to start working. However, default values can be changed in the user preferences, see below. If the background color is set to transparent, it still shows up as white in the image for enabling better annotations and drawings. When it is exported into PNG, it retains background transparency.
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