export - How do I avoid lines at top and left borders of png files exported from Illustrator

When I export Illustrator artwork as a png file, I get a one pixel grey border at the top and left edges.

There is no background object, but I export (Save for Web and Devices) with matte white background and no transparency. I also tried with a white background object, with it snapped to the artboard and also larger than the artboard by 10 pixels in each direction. I still got the lines at the top and left of the exported image.

I also tried making a new file, with the artboard in pixel units, and selected the option to have objects snap to pixel grid, and then copying and pasting the artwork from the original file. I still got the lines.

Answer

After much tearing of hair the following works for me:

1. Select View > Pixel Preview.


2. View > Snap to Pixel should be ticked.


3. You should use Artboards


4. The Artboards should be laid out by Illustrator not by you, so if you've created, copied or positioned any: Objects > Artboards > Rearrange and choose a whole pixel value for spacing. This will lay the artboards out to exact pixels.


5. Choose View > Pixel Preview and check the edges of the artwork for unwanted anti-aliasing. It sometimes helps to extend shapes beyond the edges of the artboard.


6. When you're happy with how it looks, choose File > Export and tick Use Artboards


7. Antialiasing type selection seems to have little effect on this issue but will effect the way your artwork looks.