Optimizing is a function of the refiner that allows Prinergy to effectively handle high-resolution images in the PDF workflow. Images are downsampled according to specifications in the refine process template and cropped automatically, so only the necessary resolution and image portions are stored.
Downsampling
Sometimes the resolution specified for a contone image in the desktop publishing software is greater than is needed, even for high-quality color work. The additional resolution does not enhance the quality of the image, but does make files larger. Downsampling stores the image at a more appropriate resolution. An accepted rule of thumb is to set downsampling to a ppi (pixels per inch) value that is twice the final printed line screen or lpi (lines per inch). This is set in the Optimize section of the refine process template.
Image cropping
When an image is included in a file, but the whole image is not required, the file size is larger than necessary. Image cropping removes all image information that is not visible, except for a small border around the visible image. This happens automatically during the refine process when converting PostScript to PDF.
In the example below, the entire image was stored in the input file. The area within the rectangle is the visible portion. Optimizing discards almost all of the non-visible portions of the image (a border of 1 pixel outside the bounding box is retained).