Does any one knows if it is possible and how to change
the MSX logo that appears on MSX2's after power on ?
Is this picture saved in some kind of uncompressed bitmap
or is it a DRAW or something else ?

I sent in an MRC Oneliner Challenge entry last night, called "Time for MSX". Once snout has published it as a news entry (I hope he manages to get that done some time today) you should be able to download it. Just have a look at the source code and you should be able to figure out the address of the routine in the MSX-2 ROM that does the whole MSX logo thing.
I haven't really looked into the routine itself to find out whether it's a compressed bitmap or vdp draw commands or whatever since I only needed to be able to call that routine. Shouldn't be too hard to find out how it works exactly by using a disassembler though.

P.S. if you really can't manage to find the address of the routine by looking at my oneliner then just ask me. Would appreciate it though if you'd at least give it a try

I have spend a lot of time in disassembling all the MSX-roms. I have also disassembled the MSX2-SUBROM, where the logodata is kept. I even adjusted the logo in my own.
So, yes it is possible. I have been playing with the idea to put my disassembled MSX-ROMs online. May be I will be doing this very soon. If you like, I can can send you my source of the MSX2-subrom.

Greetz, Arjen.

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I have also disassembled the MSX2-SUBROM, where the logodata is kept. I even adjusted the logo in my own.

So, how is the logo stored? Some form of compressed bitmap or vdp draw commands or...?

You also might want to check out this.

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So, how is the logo stored? Some form of compressed bitmap or vdp draw commands or...?

Yes, it is kept in line draw coordinates. For a european subrom, screenlogo setup routine starts at &H2A14 and on.
Data is kept at &H2B5F - &H2EB9.

But these addresses are not static among different (language) versions.
May be is is more simple to use the solution of BiFi.

Actually, as far as I have discovered there are 4 different types: MSX2, MSX2+, MSXturboR FS-A1ST and MSXturboR FS-A1GT. There are IPS patches (which are actually static offsets for the ROM images) for each of them. When a different one is discovered an extra IPS patch will be released for it.

@kanima: I suppose you also found out about addresses 2 and 3 in the subrom containing the address to the logo display code... with some other initialization code as well for that matter...

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@kanima: I suppose you also found out about addresses 2 and 3 in the subrom containing the address to the logo display code... with some other initialization code as well for that matter...

Yeah, but when you run my "Time for MSX" entry you'll see why I couldn't just call that whole routine. The problem being the other initialization code that is called there as well...

@bifi
So IPS are applied to rom file the result is a patched rom which logo is different.
But how different ? can we use a custom logo or the patch contains a fixed one ?
I want to use my own logo...

in this case the palette is fixed for the correct anti-alias color... Usually all color schemes (SET TITLE ,1; SET TITLE ,2; SET TITLE ,3; SET TITLE ,4) you'll notice all those anti-alias colors are gray (which is only correct for SET TITLE ,1)

to implement your own logo you need to set it up the way it's drawn by the routine... which seem to be LINE drawing commands where the coordinates are stored in the table.