Custom Windows 7 Login/Lock Background, with 256kB limit removal

[Btcc22 691]

As7raios was playing around with customising his Windows 7 background, which prompted me to do the same. We discovered that there's a 256kB limit on the background image size, making the images looks pretty terrible on higher resolution monitors. From a quick search around the web, the consensus seemed to be that this is just how things are and that there's nothing much that can be done about it.
 

 

Long story short, I had a quick reverse engineering session to figure out where this limit was being imposed and to how remove it. I'm posting this as a tutorial here because I have nowhere else to document it and hopefully other souls in search of an answer will stumble across it.
 
Before we begin, here's the usual disclaimer that applies when messing around with system files:
 

Follow this tutorial at your own risk. The only person responsible for any damage caused to your machine/files is yourself.

 

Having said that, I consider this to be a pretty low-risk modification.
 
1) First up, follow another tutorial for setting your custom wallpaper up. Disregard the bit about keeping your file below 256kB. This one should be fine.
2) Navigate to C:\Windows\System32. If you've installed Windows to another directory, head there.
3) Make a copy of authui.dll. Save it somewhere easy to access (say, C:\) and rename it to something along the lines of authui_working_copy.dll.
 

Don't worry if your file isn't the same size.

 

4) Make a copy to hack on. This will be our patched file.
 

 

5) Next up, you'll need to find yourself a hex editor. I'll be using Hex Workshop which can be downloaded here. It has a trial-period more than ample for following this tutorial.
6) Open your authui_patched.dll in your hex editor.
7)

• For 32-bit Windows, search for the following hex bytes: 3D 00 E8 03 00 73 51
• For 64-bit Windows, search for the following hex bytes: E8 03 00 41 3B C1 73 3E

8)

• For 32-bit Windows, replace the found bytes with: 3D 00 E8 03 00 90 90
• For 64-bit Windows, replace the found bytes with: E8 03 00 41 3B C1 90 90

A before and after for the 64-bit edit

 

If you're wondering what the change is, it's removing the instruction that checks the size of the file and replacing it with two instructions (called nops, or no operations) that do nothing. The 00 E8 03 00 bytes represent the 256,000 byte limit.
 

Patching done, now to replace the file

 

9) Time to replace the stock authui.dll with our patched version. There are several ways you could do this but I'll detail the method I used.
10) Reboot the machine. Hold F9 before Windows begins loading and select the repair option. We're not going to run the repair tools, it's just an easy way to access a console.
11) Once you've logged in, select the bottom option to open a command prompt window.
 

Bottom option, right there

 

12) By default, it'll place you in the X: drive, the temporary space used for booting the repair tool. Switch to your normal C: drive by typing "D:". Confirm that it's your C: drive by checking the contents using the dir command. If it's not (it won't be if you have multiple drives), go through the letters (E:, F:, etc) until you find it.
13) Now type the following commands, substituting D: for the drive letter you discovered in the previous step (if it differed).

• takeown /f D:\Windows\System32\authui.dll
• copy D:\authui_patched.dll D:\Windows\System32\authui.dll
• When prompted to overwrite the file, select yes.

Reboot and enjoy your high-res wallpaper goodness!

 

Click the spoiler button for a before and after example (saved as PNG to preserve quality). Click the images to view them at full resolution.

 

 

 

Troubleshooting, for those that dun goofed

 

Problem: Windows boots to a black screen with a cursor.
Solution: Go back to step #12 but this time copy the original, backed up, file over the patched one. You either messed up the editing or removed read access from the SYSTEM user for authui.dll - this can happen if you follow other tutorials on replacing system files.
 
Problem: Windows doesn't boot.
Solution: Go back to step #12 but this time copy the original, backed up, file over the patched one.
 
Problem: I copied the original authui.dll back but I still can't access Windows.
Solution: Run the repair tool, followed by running sfc from the command prompt (sfc /scannow /offlinedir=D:\Windows - replace D with your drive letter, if it differs).

[Skeezix the Cat 3,089]

I don't use Windows 7 anymore but when I did I wished I could change that wallpaper simply because it was shit quality for a wallpaper.  Good job!  I wonder what the reasoning for there being a limit in the first place was?  Just to be dicks?

[Btcc22 691]

I don't use Windows 7 anymore but when I did I wished I could change that wallpaper simply because it was shit quality for a wallpaper.  Good job!  I wonder what the reasoning for there being a limit in the first place was?  Just to be dicks?

My only guess is that some programmer did it on a whim for performance reasons. Perhaps they didn't want OEMs accidentally adding huge wallpapers and adding several extra milliseconds to the loading time for that screen. I've tried it with a 7MB file and it was perfectly fine, albeit on a fast machine.

Edited January 19, 2015 by Btcc22

[Solaris 3,581]

Now if only I could set nasheed .webm's as my login screen background...

[Raaage 14]

I can see the performance reasoning but damn that's a low amount, I could see XP pulling that off but I'd expect at least 1mb from 7.

[WaeV 5,049]

Well, y'know. "640 K ought to be enough for anybody"

[Pfhunkie 3,544]

Well, y'know. "640 K ought to be enough for anybody"

"100gb!? How could anyone ever use all of that!"

On a side note to Bt:

All these pixels and you still couldn't see our love.

[Dr_Fickdace 0]

HELP!! 

 

I am soo glad I found this. I have been looking for this for years actually. But I have a problem tho. I can not get the cmd outside of windows. I do not have the F8 or F9 button before the windows loading screen and when try loading the recovery tool stuff through the windws disk I installed my windows from he sais that the disk does not match the installed version of windows on my pc. Is there anyway I can fix this problem? Can't I just do it through the normal cmd IN windows?

 

Anyways, many thanks in advance!

 

 

 

-edit: 

 

Okay so I managed to fix the problem and was able to replace the file etc. BUT now the next problem is, I found out my pc just doesn't want to change the logon screen AT ALL, not even with a 212kb picture...

I did all the things with setting the "OEMBackground" value to 1 in regedit and rename the picture in the "info" map backgroundDefault.jpg OR defaultBackground.jpg but it just doesn't change.

 

So I started looking for more solutions but there doesn't seem to be any other people with this problem as far is I can find accept for here: http://answers.microsoft.com/en-us/windows/forum/windows_7-desktop/cannot-change-logon-screen-wallpaper/de3a84eb-0114-4510-87a7-563ae17f1407

But then again I bumped into another problem; I don't have any maps inside the "policies" map.

 

Also "Always use custom logon background" in gpedit.msc is Enabled

So as you may or maynot understand I am starting to get a bit desperate here.

Any help would be very much appreciated!!

 

 

Many thanks in advance!

 

 

 

-2nd edit:

 

Okay So I managed to fix the problem. I made the mistake of naming the picture "backgroundDefault.jpg'". So windows automaticly made it "backgroundDefault.jpg.jpg". Yup, I was that stupid...

That said, it works perfect now! THANK YOU SO MUCH!!!!

 

Greetings, Dr_Fickdace

Edited August 2, 2016 by Dr_Fickdace

[Vaporeon 189]

I notice an update changed this file, will the same change still apply?

[Pfhunkie 3,544]

I wish I could test it out for you but I no longer have a Windows 7 PC. I'm assuming it should still work.