Treeview space between columns

[Roberto Cavada <cavada irst itc it>]

Hi, 
 I noticed that there is alwasy a space around columns in treeviews,
even when both the style properties 'GtkTreeView::vertical-separator'
and 'GtkTreeView::horizontal-separator' are set to 0. 

E.g. look at the screenshot at
<http://sra.itc.it/people/cavada/images/Screenshot-window1.png>

In the example, columns 0 is text, and columns 1 and 2 are filled by a
rectangular (red) image that is intended to fullfil the cell. However,
as you can see there is a 1-pixel space all around each cell. 

What I'd like to implement is a treeview showing waveforms. The columns
data are images that must stay attached each other in a row, without any
space between them. When composed appropriately, a row of images would
appear as a waveform. 

Did you happen to know whether it is possible to remove the space around
the columns?

Many thanks, 
 rob