FW: FW: [Openstreetmap] Recent improvements to the editing applet

[Matt Amos]

On Wednesday 04 January 2006 20:44, Robert Scott wrote:
> On Wednesday 04 Jan 2006 18:36, Erik Johansson wrote:
> > I don't think there is much speed up to be gained from this
> > method, and the bandwidth will be doubled. But you are right it's
> > alot cleaner way fo doing things.
>
> I'm quite sure it wouldn't be doubled. The breadcrumb layer would
> probably compress out to almost nothing with PNG and a limited
> palette. (Who says we need full alpha blending? Could use a
> paletted image with orange and a transparent colour. Effectively a
> 1bpp image.)

this is a very good idea! the landsat has to be RGB, obviously, but 
the breadcrumbs could be just an A channel (allowing the user to 
choose the opaque colour!) and the roads can be a 256 colour image 
which blends from:

0 => transparent black
.5 => opaque black
1 => opaque white

since we always have a black border between the white road and the 
transparent non-road. this would also allow people to choose hue for 
the roads if they wanted...

of course, this doesn't work if we want motorways to be blue, etc... 
but i guess you could put an extra H channel in there.

so we have one RGB image, an A image and an AH image, which is twice 
as much information, landsat compresses well with JPEG and the A, AH 
images will do well with PNG, due to their large transparent regions.

but we can't say for definite without anl implementation ;-)

cya,

matt
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