[Qgis-user] Do incomplete ECW images always work?

[ardi]

I'm downloading huge ECW images, and sometimes I get a partial
download because the server resets the connection. However, to my
surprise, QGIS always reads them successfully, no matter how premature
the download was stopped.

The most severe case, for example, with just 54.3 MB downloaded while
the full file size was 1403 MB, and you can see the image with no
artifacts, no rare colors... it looks normal. I don't get any warning
message either.

Even if I zoom up to the maximum, I don't see any artifacts (although
I assume the maximum zoom level will obviously be smaller than if I
had the complete 1403 MB file).

I'm wondering if this is a feature in the ECW format. Is any ECW file
guaranteed to be successfully read no matter how prematurely the
download was stopped?

Or can you get an error in some cases?

Thanks!

ardi