Hello,

this issue is about how overlaying of maps is done.  The idea of
overlaying maps is great in general, a big improvement compared to qlk,
I really love it.  But the merged map views currently tend to look
nebulous, lacking contrast and color.

Here is an example:

https://github.com/michael-heerdegen/qms-image-quality-examples/blob/master/original.png?raw=true

This is openmtbmap + Google Maps Aerial + DEM shading.  It looks
greyish.  I tried to optimize the result by changing the order and
opacity of the maps, but it wont get much better than this if all
involved maps have to be recognizable.

Here is how the same image looks like after doing an "auto level
correction" with Pinta (a graphics program like Gimp):

https://github.com/michael-heerdegen/qms-image-quality-examples/blob/master/pinta-auto-level.png?raw=true

and here is a version were I just increased contrast + color a bit:

https://github.com/michael-heerdegen/qms-image-quality-examples/blob/master/increase-contrast+color.png?raw=true


The point is not only that the resulting images look nicer.  All
*involved maps* are better recognizable: the labels from openmtbmap are
better readable; the Google Aerial photo background looks more
naturally, and the 3D effect from DEM shading is better.

That suggests that the algorithm of how maps are overlaid can be
improved.  I don't know much about image processing sadly, but there are
three approaches possible I think:

  - use a different formula for merging the images, however that might
    look like

  - do post-processing to improve the image quality.  MMh, better than
    nothing

  - consider some parts of maps as transparent.  For example, don't
    merge the background color of vector maps.  For DEM shading, don't
    treat it like a translucent layer, but manipulate color values of
    the map view directly; e.g. darken pixels when there is a shading,
    according to the amount of shading, leave pixels as they are if
    there is no shading at that point.


What do you think?


Thanks,

Michael.

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