You seem to have asked the same question twice, and not responded to the question about your statement about "fine waveform image even the axis can be viewd even size is physically minimized" which doesn't make sense - see http://www.cadence.com/Community/forums/p/13441/20901.aspx#20901
Anyway, my guess is that you want a png with higher resolution. The way to do this with wavescan/ViVA is to use the File->Plot to plot to a PostScript file, and then use a tool such as "pstoimg" to convert it to a png file. The PostScript can then have (say) 300 dots per inch, which will be higher resolution than on the screen. .
In future we plan to improve the printing and image generation, and I believe it will then be possible to directly generate higher resolution images (as you can in IC613 for exporting images from the schematic and layout windows).