getting exact extent...

[Jaynika Barot]

hi,

i want to get the GIF image with exact extent..in my applet window of
600x400 through mapserver.
i.e 
StrURL="http://localhost/mapserver/bin/mapserv.exe?mode=map&layer=layer1&zoo
mdir=1&zoomsize=1&imgext="+Double.toString(leftX)+"+"+Double.toString(bottom
Y)+"+"+Double.toString(rightX)+"+"+Double.toString(topY)+"&map=c%3A%5CInetpu
b%5Cwwwroot%5Cms_demo%5Cdmpdemo.map&mapext=shapes&img.x=250&img.y=100";
here, what this img.x and img.y means?? From where do they come??
do i need to specify the zoom size - zoom dir ect???

or simply say i want only a gif image of the size sizeX-sizeY spcefied by
the leftX,rightX,topY,bottomY extent from mapserver,
how do i do that??

thanks.
JB