When working with a PDF hotfolder, you have the option to resample images based on a resolution set. The screen is shown below:
Resampling takes place after the MX4 color processing step when working in ColorServer but before the sharpening of images if you have that defined. Depending on your resolution needs, you will either upsample or downsample.
Downsampling is defined when the output resolution is lower than the input resolution. The number of pixels would decrease.
Upsampling requires that new pixels are added but you need to choose an interpolation method for where the non-existent pixels will be added or deleted.
Sometimes it can require a few tries to find the balance between file size and image quality.
There are 3 interpolation options:
Nearest Neighbor: This is an algorithm that looks at the points nearest to it but does not consider the vlaues of the neigboring points. This method is for sure with images that have edges that are not anti-aliased , to preserve hard edgres and produce a smaller file.
This method can produce jagged effects that can be seen when you scale an image or perform manipulations on an image. It is a quick but less precise method.
Bilinear: A method that adds pixels by averaging the color of the surrounding pixels. This method generally produces medium ressults in terms of quality.
Bicubic: Uses a weighted average instead of a simple average to determine pixel color. This method is slow but the best method and produces the smoothest tonal gradations.