The images options allow users to specify compression and resampling for graphics and images. Users need to find a balance between image quality and PDF file size.

Downsampling

Color, grayscale, and monochrome images should be downsampled to combine pixels in a sample area to make one larger pixel.

You need to provide the resolution of your output device in DPI (Dots Per Inch) and specify a resolution in PPI (Pixels Per Inch).

Typically, to get a PDF document with higher quality, PDF Vista printer driver downsamples color images above 300 PPI to 450 DPI, grayscale images above 300 PPI to 450 DPI, monochrome images above 1200 PPI to 1800 DPI.

More than often, to get a PDF file of smaller size, PDF Vista printer driver downsamples color images  above 150 PPI to 225 DPI, grayscale images above 150 PPI to 225 DPI, monochrome images above 600 PPI to 900 DPI.

You can manually set the PPI threshold and DPI value of your choice.

Downsampling Method

Three downsampling methods are available for PDF Vista printer driver. To turn off downsample, choose the "Off" option.

Average Downsampling is to average the pixels in a sample area and then substitute the entire area with the average pixel color at the specified resolution.

Bicubic Downsampling is to use a weighted average to decide pixel color. This method usually downsamples better than Average Downsampling as far as the quality of downsampled images is concerned. Bicubic Downsampling is the most precise method, but it takes time to yield the smoothest tonal gradations.

Subsampling is to choose a pixel in the center of the sample area and then substitute the entire area with the chosen pixel at the specified resolution. This method reduces the conversion time as compared with downsampling, but generates images of less smoothness and continuity.

Subsampling monochrome images can yield unexpected viewing results. If no image display happens, turn off resampling for monochrome images.

If you want to print to a 300 DPI printer, you would need 120 PPI for resampling images. 600 DPI needs 170 PPI. 1200 DPI needs 240 PPI. 2400 DPI needs 300 PPI. Therefore, 300 PPI is the default threshold, which is adequate for most printers (from 300 DPI for up to 2400 DPI printing resolution).