Im having a hard time with the quality of PNG files exported from vectors I have created in Xara. Ive tried tweaking the anti-aliasing, and have tried scaling the original image to be a closer size to the output, but the images are still low res and blocky when I try to put them in my website. Ive also tried using different output formats, but they are still blocky in JPG and BMP. Can anyone twll me what the trick is to get PNG's to export and retain decent quality?

One of the pictures I am really struggling with is about 20mmx20mm. Its so blocky the text is unreadable. What do I have to do to get it to look the way it does in Xara before I exported it?