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I am not familiar with Corel Painter. But I know that it is a pixel editing application, like Photoshop. And unlike a CADD program that works with vector objects, it works with pixels. Hence in a vector application an object is defined with a scalable outline, in a pixel editing application, an image is defined by a grid of colored pixels. The two approaches are very different.

My guess is you need to make a selection of the image or object using any of the selection tools, and then scale the image downward to a specific size or percent. Look in the Help menu for Selection and Scaling.