Options on this window are used to configure downsampling for monochrome images, indexed images and high color images.
The dialog can be opened by pressing the Configure button from the Graphics window in Printing Preferences.

Enable downsampling
If checked monochrome, indexed or high color images will be downsampled. That means the images will be added in the PDF file at a different resolution then the one from the original document. Usually, this feature is used to save images at a lower resolution, resulting smaller PDF files.
Resolution
The image resolution can be selected between 72 dpi and 2400 dpi. By default the resolution is 96dpi.
Method
Available downsampling methods are: Box, Bilinear, B-Spline, Bicubic, Catmull-Rom, Lanczos. By default, the Bicubic downsampling method is used to downsample images to the selected resolution.

