Displays images with inappropriate size

[andymathieson]

When running an audit on mobile, or if I run an audit on a 4k or 5k monitor where the DPI is 2x, we get marked down on our score.

In the screengrab above, you can see that lighthouse is expecting an image of 2198x2150. You can also see that the image being served has the dimensions of 2200x1252. However, the displayed size and actual size don't correspond.

I get a 100 if testing on a standard dpi monitor.

[patrickhulce]

Thanks for splitting this out into another issue @andymathieson!

I can reproduce this on http://melodic-class.glitch.me/image-srcset.html which reports the 800x400 source image as only 360x180.

[patrickhulce]

@andymathieson are your images also served after a redirect from the original src attribute? If so we've found the same root cause.

[andymathieson]

Hi @patrickhulce

We do use lazyloading from a Src Set. So we actually have a data-src-set. I can understand it if lazyloading threw a bug, but that should also happen at a standard DPI should it not?

[patrickhulce]

I'm not sure I understand your response. I'm asking if the image URLs you reference in your src/srcset/data-srcset return a 301/302 redirect to the underlying resource (as many image CDNs seem to do).

If they do, then I have found the cause of the bug.

If they don't, then I cannot reproduce what you're talking about and there's more than one issue going on here (so we'll need a public URL or more detailed reproduction information from you in order to help).

[andymathieson]

No problem. I can't post to a clients website but I will build a little mockup in the next day or two. Thanks

[patrickhulce]

No problem. I can't post to a clients website but I will build a little mockup in the next day or two. Thanks

Does this mean those images do not redirect then? :/

And awesome, thank you that would be great if it's different!

[andymathieson]

I have tested 2 systems. 1 with CDN, one without. The results are the same. We use cloudfront for CDN and I havent added any redirects unless Amazon does it of its own accord. That wouldn't explain the non-CDN version tho.