Unfortunately, there is no quick solution to removing screen burn. What has happened is that the phosphors have more wear in certain places, when in turn produces a shadow in the image when projected. On plasma and ordinary CRT TVs, the screenburn may even be visible even with the TV off.
As far as I'm aware of, apart from having the tubes replaced, the only other way to reduce the screenburn is to actually wear the rest of the phosphors to the same level of the screenburn, which in theory would give a clean (but darker) image. However, before attempting anything, I would definitely recommend checking if there is still any warranty on the TV and whether screenburn is covered.
The following process is quite tedious,requires at least some basic photo editing skills, photo editing software, a digital camera and a HD media player capable of showing photos without a border. I haven't tried this, so I cannot say for certain how well this process works, so if you know you'll end up having to fork out on replacement projection tubes, it might be worth the following at your own risk:
- Show a full screeen pure white image, e.g. white JPEG photo from a HD media player.
- Take a photograph of the screen directly head-on, with the minimal possible skew, barrel and pincushion distortion.
- Adjust the levels in the photograph such that the darkest part of the screenburn showing turns black.
- Play this photo on a HD media player and check that the screenburn in the photo aligns up exactly with the actual screenburn.
- If necessary, edit (trim, expand or move) the photo such that it aligns when displayed and that there is no border around the image.
- Once aligned, display this photo for a few hours, then check with a plain white image to see if there's any effect.
- Repeat displaying for longer periods if necessary until the screenburn is no longer significant and where it becomes acceptable in ordinary TV viewing.