New to Java

I'm managing since few days a java applet that takes an image from an industrial product and shows it in a browser (simple web server).
There is following issue: the image is not correctly loaded and refreshed in its own window if just opened but only if the applet is running on Windows 7. The issue is solved as soon as I reduce the window to icon (minimize) and then resize it. I'm looking into java documentation on how to manage the image rendering, maybe I have to override some update or redraw method more, but it is taking time and I'm still learning. NOTE that the window opened does show the issue only when the windows size is not completely shown in the monitor.
Meanwhile I'm wandering if some of you faced and solved similar problem.
Thank you in advance,
Elena