[mapguide-internals] Raster performance (wasRasterproviderproblems...)

[Traian Stanev]

They were two PNG attachments at 11K each. Not sure why they didn't make it.
It's not as bad as JPG output in that the dithering artifacts are local and aren't visible in an 8x8 square around sharp contrast edges like JPG.
I have played with PNG compression settings and when set to the max, an enormous time of rendering is spent compressing the PNG. On some of my maps around 50% of rendering time is PNG compression alone, and that's using the default zlib compression setting (6 out of 9 IIRC). At 9, it's unbearably slow for not much better compression than the default level.
8bit PNG output is something to consider, but we have to have in mind the drawbacks -- a map author would need to be smart about how many colors they use in their map for example. On the other hand, Google Maps manages to look ok with 8 bit PNGs. I suggest you put it an enhancement request.
 
 
Traian
 
 

	-----Original Message----- 
	From: mapguide-internals-bounces at lists.osgeo.org on behalf of Jason Birch 
	Sent: Sat 4/7/2007 10:31 PM 
	To: MapGuide Internals Mail List 
	Cc: 
	Subject: RE: [mapguide-internals] Raster performance (wasRasterproviderproblems...)
	
	

	Hmm.  Attachment didn't make it through to me.
	
	I believe you that it's ugly.  Is it as bad as the JPG output?  I'm basically wondering if there is anything better than JPG at similar size.  Maybe control over the JPG compression level would be useful?
	
	There are still a number of residents that are on dial-up, and large PNGs are not going to work for them.  It's too bad that SVG isn't more widely accepted :)  I've gone with image-based mapping because of the headaches I've had trying to deal with ActiveX controls (annoying Linux & Mac users to no end) over the past years, but client/server was  probably a better solution for low-bandwidth users.
	
	Jason
	
	________________________________
	
	From: Traian Stanev
	Subject: RE: [mapguide-internals] Raster performance
	
	My chief concern with dropping down to 8 bit color output is that it means we would have to turn off antialiased drawing. Compare the two attached images to see what happens when you save a map that uses antialiased drawing into a png8 image. I used GIMP to generate the optimal palette for the 8 bit image, which by the way is time consuming also, so regular 8-bit output would likely be worse.