Hi @user53 -
Sorry to hear it didn't work for your theme. I haven't used Narrative so I cannot say definitively - but another option is trying to use an .svg file instead of a .jpg or .png. Since .svg files are relative to plane they will not pixelate no matter how much you zoom!
The way to get this is a little tricky even in debut and it requires some tampering with Section .liquid files so I would suggest making a backup copy of your website before trying this. Again, I know this works for Debut but it may not work for Narrative.
Try this support page for uploading an .svg logo if you need any more help let me know! The support page is for a header, but I am sure you can make the same changes in your password-page.liquid.