Down sampling guidance for raster content in SVG.

In creating SVG versions of our current CGM sets of bitonal and grayscale graphics, we discovered that the way browsers implement their downsampling varies widely.

Specifically, IE and Firefox seem to just downsample by dropping rows and columns out of the raster content as they render the SVG.  Sometimes they do better with a PNG image, but not always (IE9 does very odd things - behaving differently if you directly zoom out with ctrl-'-' vs click on the image with the IE (+) and (-) magnifying glass first, which seem to take the PNG to a different behavior mode for later ctrl-'-' reduction in size).  Chrome does a good job and properly anti-aliases the SVG raster content as it reduces the size, converting the image to greyscale if it was bitonal by the looks of it.

The short of it is that IE and Mozilla are not usable for displaying SVG graphics containing line art raster content, if one has to reduce the size of the graphics into a smaller frame, as the artwork starts to disappear and become unrecognizable.

It may be worthwhile considering adding some guidance recommendations for SVG viewer implementations along the lines of it being recommended that SVG raster content be anti-aliased and internally stored and even rendered in a larger color space if necessary (eg bitonals become grayscale, etc) for the purposes of rendering the SVG.

Thoughts?

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Thomas Smailus
The Boeing Company