Thanks Masa,
I have followed the same steps and able to view the logo in preview mode on browser, but when i save and load the theme, the image seems to be broken, i can not see the logo on launchpad, where as i have changed the color coding for launchpad and i can see that change happening on launchpad.
As soon as i save and build, the image vanished from Launchpad.
the UI5 libraries 
version as 1.28.23.