this problem happens in the rendered images, I think there must be some way to get rid of the issue. any idea ?

? Do you use heavy anti-aliesing ?

Ya turn the rendering quality up. Try Ultra or user and if your using Volumetric skies then turn the quality of the fog up lots you can go past the three there by just typing in new numbers. I've done +6 and even +8. If you using bmp images for textures make sure there set to bycubic in the over sampling part and make sure your not exceeding the texture sizes, like don't expect to cover something big with a tiny little bmp texture. DELETE JPG textures there useless ! People over compress them then there almost a total waste of time. The boxes of the jpg compression system will show up. It don't work that way. Vue will not draw a better texture you must have it big enough to start with or if it's seamless make sure you set it to tile. To cut down on the rendering time Group and then group some more. Repeat after me " Grouping is my friend !" This program can blow any program away in rendering quality just don't be in a hurry. It's got total control on the rendering quality setting and that may be good or bad cause people don't know how to set up all the options. If in dought use Ultra. The fog setting will make the biggest difference if your using Volumetric skies. Try little tiny test renders till you get the effect you want. Like put the main scene view on it's own screen then select render area around the trouble spots in the scene and render them out with differnt settings till you get the effect you want. Then render the whole works the size you want.

Well, most hast already been said. For good renders, use a higher quality setting (best is user settings with everything enabled) and higher anti-aliasing settings. Also, if you're using dim lighting, you might encounter render artifacts. -Sascha.rb

i like vue, but the only reason i don't use it much is the grainy image. I will try your suggestions to use higher quality. :)