Disable Desktop Wallpaper JPEG Quality Reduction in Windows 10  

Kishvand said:

Hello, this is also my problem: on some forums including Microsoft I found it should be 100 in decimal and 256 in hexadecimal, please anyone any help?
I am sure a i7 8700K & 64GB of 3200MHz Ram with a Samsung 970Pro 1TB considers decent performing system?

Hello,

100 decimal is equal to 64 hexadecimal.

This number designates the quality of the image, so setting the value to 100 decimal or 64 hex is to use full quality images with no compression at all.

Basically 100% of the quality.

Xolaste said:

Does this also happen in Windows 11? If yes, can I use this workaround for it?

Hello, and welcome.

I just tested on my system, and it's still the same in Windows 11.

The size of the TranscodedWallpaper file is smaller than the original JPG file by default.

Disable Desktop Wallpaper JPEG Quality Reduction in Windows 11 Tutorial | Windows 11 Forum

Hey @Brink
I think something is wrong because when you set JPEGImportQuality to 100, it actually doesn't disable the conversion. You know that JPEG format is a lossy format, so even when you set it to 100%, you lose a bit of quality. Also, Windows uses a JPEG image located in the CachedFiles folder as a background wallpaper, which always has 90% quality even when you set it to 100%. It seems it's generated from TranscodedWallpaper, so Windows first reduces the quality to 85% and then reduces it again to 90%, resulting in 76.5% of the original image quality, but with an additional conversion, which makes it even worse.
On the other hand, the quality reduction is not noticeable by common users when you set it to 100%, but you can take a screenshot and compare it with the ICAT or JpegView, then you will notice the changes.
Another parameter is the quality of your JPEG image. Let's say I have a 4K JPEG image with a quality of 60% and a size of about 1MB. In this case, if you set the JPEGImportQuality value to 100, it will not give you any extra quality and will only increase the size of the TranscodedWallpaper file to about 10MB.
I don't know, but it looks like Windows itself is trying the wrong way. Why does it need to be transcoded? Why not draw it like other popular and fast image viewers to avoid extra read/write to the system disk too if it's on another disk?
Anyway, if you want to stick with this behavior, I found that a value of 90 is a sweet spot, while not reducing the quality too much and also not increasing the TranscodedWallpaper size too much (in the example above it will be about 2-3MB).
Also, after some trial and error, I found two ways to disable conversion completely to set your actual JPEG file as the background at its actual quality and size (the value of JPEGImportQuality doesn't matter anymore):

Method A:
1 First, in File Explorer, select "view" and then check the "File name extension" checkbox (another way: Folder Options > View > uncheck "Hide extensions for known file types" > OK).

2 Copy your image to "%AppData%\Microsoft\Windows\Themes".

3 Delete TranscodedWallpaper and rename your image as TranscodedWallpaper (without any extension) and press "Yes" in the warning message.

4 Go to "%AppData%\Microsoft\Windows\Themes\CachedFiles". There is a JPEG file (restart explorer if there is no CachedFiles folder or JPEG file). The name seems to depend on your monitor resolution and wallpaper position setting, e.g CachedImage_1920_1080_POS3.jpg. You should replace it with your original JPEG image, just make another copy of your original image and rename it to the name of that JPEG file. Then paste it there and select "Replace the files in the destination".

5 Right-click on the replaced JPEG there and select Properties > Security > Advanced > Change > Advanced > Find Now > choose Administrators in search results > OK > OK > Disable inheritance > Convert... > delete all users in the Permission entries: by selecting them and pressing Remove and just keep SYSTEM and Administrators > OK > OK.


6 Restart explorer to make the changes take effect.

Method B:
1 Do the same as steps 1 to 3 of Method A.

2 Instead of changing the security settings, just delete the CachedFiles folder, then create a text file and rename it as CachedFiles without the .txt extension. Restart explorer to make the changes take effect.

Note1: I will try to write a batch script to do the steps above automatically. When it's done, I will update my post here.

Note2: Doing only step 2 of Method B will disable second conversion and give you better quality if you have already set JPEGImportQuality to 90-100. The quality is not the same as the full of Method A or B, but it's not worse than the default. Here is a quality comparison with 400% and 1000% zoom (the changes are often noticeable in red and green colors):


From left to right (best quality to worst):
full-org : The result after doing Method A or B (same quality as original file).
100+dummy: Setting JPEGImportQuality to 100 and doing step 2 of Method B (disabled second conversion).
90+dummy: Setting JPEGImportQuality to 90 and doing step 2 of Method B (disabled second conversion).
100-dummy: Just setting JPEGImportQuality to 100 (with default Windows double conversion).
90-dummy: Just setting JPEGImportQuality to 90 (with default Windows double conversion).

Conclusion:
It seems the problem is double conversion, not the quality reduction itself. If you look at the comparison above, you will notice that 90+dummy has better quality than 100-dummy while both result in 90% of the original quality. The only difference is the double conversion."

Hello @amymor,

Of course, using a PNG file will avoid all of this.