I have used precisely the same export/import trick as you in order to use
the Mathematica rendering engine to generate bitmaps for use in image
processing applications. My cure to the extra white space problem was to
simply discard those pixels after Importing the bitmap, and to anticipate
this loss of pixels by Exporting a slightly larger bitmap in the first
place.

I have just tried to reproduce what I did using Mathematica 5.1 (for
Windows) and find that the extra whitespace problem seems to have been cured
in that version. However, here is (roughly) what I did to cure the problem
in an earlier version of Mathematica:

Load a package for generating a pretty image.

<< "Graphics`Shapes`"

Generate an image (with a black background so you can see the extra white
space when it is added), export, then import it. Notice that I export 1
pixel more in each dimension than I eventually need.

g = Show[Graphics3D[Torus[], Background -> RGBColor[0, 0, 0]]]
Export["temp.bmp", g, "BMP", ImageSize -> {101, 101}]
g2 = Import["temp.bmp", "BMP"]
Show[g2]

Now have a look at the contents of g2. The first part is the image data, so
I have displayed only its dimensions. This shows which bits have to be
changed if you crop the image. There may be an "official" way of doing this,
but I haven't found it.

Dimensions[g2[[1,1]]]
g2[[1,2]]
g2[[1,3]]
g2[[1,4]]
g2[[2]]
g2[[3]]
g2[[4]]

{101, 101, 3}
{{0, 0}, {101, 101}}
{0, 255}
ColorFunction -> RGBColor
ImageSize -> {101, 101}
PlotRange -> {{0, 100}, {1, 101}}
AspectRatio -> Automatic

Make a copy of g2, and then hack it to crop the image. I am dropping the
last pixel in each row, and also the last row of the image. I am doing this
from memory, so if this prescription doesn't get rid of the white space then
modify it appropriately.

g3 = g2;
g3[[1,1]] = Drop[Map[Drop[#,-1]&,g2[[1,1]]],-1];
g3[[1,2,2]] = g3[[1,2,2]] - {1, 1};
g3[[2]] = g3[[2]] /. {x_, y_} -> {x - 1, y - 1};
g3[[3]] = g3[[3]] /. {{x1_, y1_}, {x2_, y2_}} -> {{x1, y1 - 1}, {x2, y2 -
1}};
Show[g3]

Have a look at the contents of g3.

Dimensions[g3[[1,1]]]
g3[[1,2]]
g3[[1,3]]
g3[[1,4]]
g3[[2]]
g3[[3]]
g3[[4]]

{100, 100, 3}
{{0, 0}, {100, 100}}
{0, 255}
ColorFunction -> RGBColor
ImageSize -> {100, 100}
PlotRange -> {{0, 99}, {1, 100}}
AspectRatio -> Automatic

That should do what you want.

Steve Luttrell

"Jan G. Korvink" <korv...@t-online.de> wrote in message
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