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When booting, the first screen shown by the N800 is all white with a logo in the middle. The logo is /usr/share/icons/hicolor/scalable/hildon/qgn_indi_startup_nokia_logo.png and is 416 x 72 pixels.

Must the ...logo.png file be exactly 416 x 72 or can it be made quite a bit bigger? Presumably it can not be 480 in height because of the blue scroll bar along the bottom during booting.

I would like to make a ...logo.png about, say, 600 x 400 pixels. Would this cause a crash or stop the N800 from booting? As I'm a total and complete Linux novice I can't afford to make my N800 unbootable as I would have no idea how to get back to replace the ...logo.png with the original file.
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The logo can be full size. It can also be a JPEG. (Disclaimer, I modified the startup scripts to point at a different file, rather than replace the file, so I don't know if it determines the image type by the file extension or by actually looking at the data format in the file itself).

I made custom startup screens for my N800 at 800x480 (I replaced both the Nokia logo and then the "hands" screen). The progress bar is not a problem, it is overlayed on top of the background image.

And as to restoring a broken N800 install - you simply re-flash it. Of course, this means you have to re-install everything, and hopefully you have used the backup/restore tool to save all your data before you go making changes that might possibly brick your N800.

Can you point me in the direction of the start-up scripts that control which images are displayed? Not sure at this point where to load the revised images and how to get them called.

Thanks!
k