[css3-images] 'image-resolution: from-image' based on resolution X / Y

Hi,

In TIFF and JPEG (EXIF), the resolution metadata can be specified as two 
fields: Resolution X and Resolution Y. Although I expect the two to be 
the same (when set at all) in most real images, what should a UA do when 
they’re different? 'image-resolution: from-image' expects a single value.

I think there is no good answer to this, but I dislike leaving it 
undefined. I suggest specifying something arbitrary. For example:

     If the image specifies two different resolutions for the horizontal 
and vertical direction, the average of the two values is used:
     <code>(horizontal + vertical) / 2 <code>


-- 
Simon Sapin