No it is not a Matte, nor a stroke. I made sure Matte was unchecked when Exporting for Web and that the stroke color was null.
I am working in Illustrator exporting an image for a webpage table background. But it keeps exporting with a thin white boundary(b/c jpeg format chosen, border could be transparent as well if gif/preserve transparency selected).
The composition is just a rectangle(no stroke) with linear white-black gradient, then another rectangle(no stroke) sitting directly on top acting as a path for a text box. I pasted some text into the box and then reduced the transparency. So, it looks like a page of text that fades to black from top to bottom.
In the save for web preview box when I toggled through the various formats, I can see the thin white or transparent border, depending on the format/transparency. It is thicker on the right side, maybe 2 pixels on left, 5 pixels on right.
Check the info palette to make sure the object size is in whole numbers.
Than, either make the artboard match the size of the object, or move the object so it's top-left corner is at the 0,0 position of the artboard (also a top-left corner).
This assures that your object is properly aligned within a pixel grid.
A few years answering this one, but still it might help someone.
Get the exact measurements of the image for example 900 x 900 pix
open a new window make the background colour whatever you need it to be, resize the background you need to 910 x 910 pix so it overlaps the artboard, paste your image on the top layer, hit export, in the export window click the image size tab, check "clip to artboard" and bingo no white lines even using matte colours.