Image rendering issue with the native email application on iPhone

I've created a adaptive mail template for a client that uses mostly images in her mail campaigns. The mobile view looks great on the Litmus Android devices, but somehow the images get vague on iPhone: (check the face of the young girl).

Because the images the client uses aren't all that good to begin with, I've send the min-width of the table to 300px, thinking that should be enough to show the image in the same format as the desktop view (4 columns x 150px, become 2 columns x 300px)

Now I know iPhone scales mails to fit the screen, so it would be that the images are shown very slightly smaller than the 150px they are. But that doesn't explain why the images get vague.

Any ideas? Or is the iPhone image render engine just not as good as Androids (which I can't really believe).

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