plotting - Opacity and overlapping multiple polygons

Let's say I have 100 polygons that are all different but most of them overlap. All I want to do is to draw/plot them in one single graphic with linearly adding gray values; i.e., a point with n overlapping polygons(or other graphics) should have a grayvalue of n/100.

I wish

Graphics[{Opacity[1/10], Table[Disk[{i/10, 0}], {i, 10}]}]

would work, but Opacity doesn't add up linearly, and I don't find any easy way to do what I want.

My current idea is to go via Image[Graphics[...]], ImageData and ArrayPlot, but I might lose a lot of precision that way.

Answer

I'm not very familiar with image-processing but I do not think you could get both, high precission and high performance, at once.

This is straightforward approach. With Image processing functions avalible in Mathematica. Also, I'm not going to use Opacity, I do not know how does it work inside.

First, there is a function to to create an image, you can set resulution like you need.

f = ColorConvert[Image[Graphics[#, PlotRange -> 1], 
                       "Bit", ImageResolution -> 96, ImageSize -> 500], 
                 "GrayScale"] &;

Lets create some triangles:

pics = f /@ (Polygon /@ Table[{{0, -1}, RandomReal[1, 2],RandomReal[{-1, 0}, 2]}, 
                              {100}]);


ImageMultiply[Fold[ImageAdd, First@pics, Rest@pics], 1/100]

Stealing examples with Disks (generating disk images last longer but not so much):

f = ColorConvert[Image[Graphics[#, PlotRange -> {{-1, 1}, {-.5, .5}}], "Bit", 
                       ImageResolution -> 96, ImageSize -> 500], "GrayScale"] &;

pics = f /@ Table[Disk[{-.5 + i/100, 0}, .5], {i, 100}];


ob = ImageMultiply[Fold[ImageAdd, First@pics, Rest@pics], 1/100]
ColorNegate@ob

As you can see, everything is linear:

ListPlot[ImageData[ColorNegate@ob][[ 130]]]