Save Impress Slides as Images
Export File Formats
LibreOffice allows to export single Impress slides as images, by accessing the menu File > Export…, and then by choosing one of the available file formats. Using this feature, exporting all the slides of an Impress presentation is a rather tedious operation.
Luckily, there is a LibreOffice extension which allows to export all slides as images in a single operation. In addition, it allows to choose the file format and configure the output.
LibreOffice Extensions website
To install the extension Export as Images, you have to access the LibreOffice Extensions website, search for the extension, download the OXT file, and install it using the Extensions Manager (which can be accessed from the menu Tools > Extension Manager…, then clicking on the Add… button, and following the instructions).
Export as Images Dialog Window
Once installed, Export as Images creates a new menu entry File > Export as Images…, which opens a dialog windows where you can choose the directory, the file name, the file format, the size (by entering the requested width or height in pixels), and color/grayscale.