AlpineQuest & OfflineMaps

Ok sorry of course I meant opacity...

I found a good solution with storing a favorite "compare" set, and the "compare" slider displays automatically. Great!

I am wondering what could be the cause of the quality deterioriation when comparing the original data and the alpinequest image?

Edit:

A similar deterioriation in image quality occurs when using plain image maps.

A 60 Mb .jpg file is imported and turns into a 38 Mb .pgd file...with less resolution...

I am wondering what could be the cause of the quality deterioriation when comparing the original data and the alpinequest image?

You're not comparing the same images.
In the AQ screenshot, you can see there are some inlaid information (I can read "2019" and "geoland...") which is not added by the application. So even if the original image is the same, the one displayed in AQ had an extra processing done before being accessed by (and outside of) the app.

A similar deterioriation in image quality occurs when using plain image maps.

When importing images as maps, the application will (re)compress the imported images with its own parameters that are a good compromise between size and quality.
By default it uses the WEBP image format (with a claim of up to 34% less size than JPG for the same quality), and a compression quality of 80%.
If you don't care about size and just want the maximum quality, you can increase the compression quality with this user setting: You can also force the application to use the JPG format with:

You are right, it´s not the same data.

I contacted the folks at basemap.at and they say that they do not know the cause, but they will check it.

Concerning the imported maps, I guess I can also use .bmp instead of .jpg? Like ...image_format=BMP ?

What is the largest file size the app can handle?

For the image formats, you can only use "PNG" (lossless), "JPG" (quality based on the "image_quality" parameter, from poor to almost lossless) and "WEBP" (quality based on the "image_quality" parameter, from poor to almost lossless).
Note that the PNG and WEBP formats support transparency, JPG not (so it's not suitable for layers with transparent background or areas).