three problems when manipulating graphics

[Philippe PEZARD]

I'm trying to convert a stack from hypercard to revolution and I meet 
some problems. Is there somebody to help me ?

1°) I'm surprising to see that coordinates of pixels on a card begin at 
-3, -25 (top left) and end approximatively at 600,400 (bottom,right) in 
a stack defined with 600 * 400 window.

2°) i would like to use instruction like "click at 200,300" with bucket 
tool in several part of a graphic to make these parts dark. Sometimes, 
Results are wrong (that's not the expected part that become dark) as if 
coordinates of the "clicked" point were false nevertheless I determine 
these coordinates using the mouseloc() function and spell them in global 
variables (set to empty between two selection)

3°) in the scrip below (that replace working image by the original), the 
instruction "choose browse tool" don't work properly. When i move the 
cursor out of the button that command this script, the select tool 
replace immediately the browse tool.

on mouseUp
   lock Screen
   select card image "Schema.png" of cd "SCINTI QUANTIF1"
   delete
   import paint from file "/Disque X/Revolution 1.1.1/Schema.png"
   set the layer of card image "Schema.png" to bottom
   set the opaque of cd image "Schema.png" to false
   unlock Screen
   choose browse tool
end mouseUp

Many thank's !  .... and i apologize for my very bad english (french 
student)