The picture use as background increase dramatically the size

[.·:m·a·r·l·a:·.]

Hello everybody:

quite happy i found this place, i hope you can help me in this error I
dealing with

I have a excel file with three sheets in which, among some formats and
formulas i insert a picture as backgroud (format -> sheet -> background)

the picture I insert is a 90 kb file, bmp, 1 pixel high, 32000 pixel long,
resolution 96 dpi and 24 bits depth colour

the original file is about 555 kb, containing 3 of this pictures, one per
sheet

then i soupose
90 x 3 = 270 kb becouse of the pictures
555 -270 = 285 kb becouse of the rest

the file i send to some person, this people fill some data and I receive
back

the file is bloqued for everything (sheets, workbook) except those cells in
which i expect them to input data, this meaning that the user can not make
any formating, only key data

when i receibe the file it is arround 9 mb

saving each one of the sheets separatly, they are about 3 mb
saving the file after unprotect and delete the backgrounds it comes to 350 -
400 bytes (dependly the file)

if the original file without background was arround 285 kb and the new one
with background removed is about 350-400 kb, i soupose that the person has
input arround 100 kb of data (it could be acording the amount of data they
have to key)

but what could has happend with the background to increase from 90 kb to 3
mb ??

please give me any help acording this one, it is a mistery it start to turn
me crazy

thanks in advance

 

[.·:m·a·r·l·a:·.]

nobody know nothing about it ???

please, just a bit of help, this problem is making me crazy