Hi Saurabh,
When you save the image, you can specify the size of the PS, EPS, or PDF plot using the /XINCH or /YINCH command line options for the FRAME command. So you can have it create a bigger "100%-size" image if that looks better to you.
But since these are vector images, there really is no "DPI resolution" like there is with raster (PNG, JPEG) images. If you zoom in close to a piece of a PS, EPS, or PDF image, it should show crisp lines. The contents of vector image files are basically drawing instructions. If it looks blurring to you, it probably is due to limitations of what can be displayed on your screen. But again, zoom in to part of the image to check.
If you encounter the thin white lines in what should be solid color areas, consider adding the /OUTLINE=... option to the SET WINDOW command. This option draws a thin outline (width in "pixels" specified by that option) around all blocks that PyFerret plots. Using the smallest number that solves the problem is best, so try values like 0.01 or 0.1 at first for displayed vector images. (When saving PNG images from undisplayed plots, you might need to use values as high as 0.75.)
Karl