I think what you are seeing is the result of the small default systray icons (32x32 pixels I think) being enlarged to the size that you are displaying them in your systray dock (for example 96x96 or 128x128 or 256x256).  Taking a small image and making it a lot bigger will make it fuzzy or pixelled.

The easiest way to get rid of that is to set the systray dock to display them at 32x32 or close to it.  But you quite likely don't prefer them that small.

You can change the image OD uses for each systray icon to a larger image, similarly to changing the image for any other dock icon.  Instead of right-clicking on the dock item though, you have to [ctrl]-left-click on it or maybe [alt]-left-click on it, not sure which and I can't check right now.

A few systray items are stubborn about keeping the new image though and will tend to switch back to the default, especially if their programs update frequently, so you'll either find yourself constantly changing those or just leaving them.  Most will hold though.