Poor image quality

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Poor image quality

Postby andrea.ippo » Sat Jan 01, 2011 12:59 pm

I'm using WPC Lite 3.6.0.180 on Win7 Professional, and I've noticed that the wallpapers are rendered with a poor image quality, compared to other similar programs (e.g. Wally, but also XnView's set image as background feature).
I've changed every possible setting in WPC that I thought might determine this (wallpaper position - stretching, tiling, centered, etc), and also disabled the feature to fill the empty part of the screen with a color similar to the one in the current picture. But nothing changed.

So I opened the folder where WPC temporarily stores the current wallpaper, and surprise surprise, it's perfect!
So I don't know where in the "chain" this degradation occurs, but somewhere it happens, and it seems that WPC is somehow responsible for it.

Some links:


Original wallpaper file (1280x800, 2,93MB, PNG):
Image


Screenshot: WPC's rendering (notice the red "Firefox" text)
Image


Screenshot: rendered using XnView's "Set image as background" feature (or any other wallpaper manager)
Image
In this case, the Image stored by XnView in "C:\Users\<username>\AppData\Roaming\XnView", is in BMP format and has the same size of the original PNG file (2,93 MB).

Image stored by WPC in "C:\Users\<username>\AppData\Roaming\NuonSoft\WallpaperCycler":
Image
This image is in BMP format, but is 3,90 MB in size.


I highlighted some format and size info because I find it strange that WPC changes the image size while XnView does not, so maybe this is somewhere to start the investigation from.


Thank you
andrea.ippo
 
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Re: Poor image quality

Postby Marc G » Thu Jan 13, 2011 12:10 pm

That's rather strange. As you can see, the BMP generated by WPC is perfect, but then somehow is not displayed perfectly by windows.
I don't immediately know what could be the problem but will take a look at it when I find the time.
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Re: Poor image quality

Postby andrea.ippo » Thu Jan 20, 2011 1:07 pm

Yes, that's really strange.
If you need them, I can provide the original BMP files
andrea.ippo
 
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Re: Poor image quality

Postby Marc G » Thu Jan 20, 2011 1:21 pm

Yes, please send me the original BMPs.
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Re: Poor image quality

Postby andrea.ippo » Fri Jan 21, 2011 8:44 pm

I've uploaded a zip containing:
  • the original image file (PNG, 2.93 MB)
  • the BMP that results when setting the mentioned PNG as wallpaper using the XnView shell extension (2.92 MB)
  • the BMP that results when WPC sets the mentioned PNG as wallpaper (3.90 MB), using "Stretch to fill"
  • WPC settings as .ini
  • my wallpaper collection list

Mediafire link:
http://www.mediafire.com/?079oi4gv3je6vlv

Thank you
andrea.ippo
 
Posts: 4
Joined: Sat Jan 01, 2011 12:39 pm

Re: Poor image quality

Postby Marc G » Sat Jan 22, 2011 7:51 pm

I ran some tests with your Firefox image.
First, I tried with WPC and then I saw some re-compression artefacts on the desktop.
Then I tried to set the wallpaper directly in Windows using your original Firefox image, and then I also see artefacts.
When I view the images in a photo-editor program (the original and the one from WPC), I don't see any artefacts.
So apparently Windows is doing some recompression behind the scenes.

Maybe I can find a workaround for this in a future version.
Marc Gregoire,
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Re: Poor image quality

Postby andrea.ippo » Sun Jan 23, 2011 10:40 am

I've made some additional tests and actually the degradation occurs also when using Windows (Seven) built-in feature to set wallpapers, which I didn't notice before.
So it seems like Xnview and others use some mechanism that bypasses Windows feature, while (just making an hypothesis) WPC relies on it, hence the degradation

Anyway, thanks for taking a look at it :), since currently a lot of my abstract wallpapers are unusable because they are rendered with similar artifacts

PS: would it be useful to let you know how WPC renders the same wallpaper on Win XP, or have you already tried that?
andrea.ippo
 
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Re: Poor image quality

Postby Marc G » Sun Jan 23, 2011 1:26 pm

I didn't try the Firefox image on Windows XP yet.
Actually, I wouldn't be surprised if Windows XP renders it differently compared to Windows 7.
I think I know how to make a workaround for this issue on Windows 7, unfortunately, that takes time and right now I'm swamped with work because I'm currently writing for my book "Professional C++ Second Edition" (Wiley/Wrox). Once that is finished, I hope I finally find some time to work on Wallpaper Cycler.
Marc Gregoire,
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