[plt-scheme] 5-6 seconds to run my prog ??

Hi,
I work on a scheme project, (I'm a student)

I have a canvas & a double buffer,

When, I load a bitmap  for my background, why my program, does take  5 or 6
seconds to run????,
(my frame appears 5 or 6 seconds later)

(my bitmap  => 800 * 400 px, and I try png or jpg )

so I put just this :
(define img  (make-object bitmap% "bg.jpg" 'jpg  #f))
in a new window: I run --> same problem

but when I use small bitmap (4*4 px ) it's OK no delay.

*how to reduce this waiting? *

because I use 6 or 7 different backgrounds.
so when my frame appears and I swap my background there are no waiting it's
really just the initial loading.

thanks

-------------------------------------
my config (e6750 3.2ghz, 2go ram etc.... i try on windows xp pro, ubuntu)
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