TTF vs OTF rendering difference on Windows (darkness/boldness)

[herrernst]

Out of curiousity I've compared the OTF and TTF webfonts (WOFF). I've noticed that on Windows 7 or 10 (IE, Chrome, FF, all using DirectWrite IMHO), the OTF looks bolder/darker.

https://rawgit.com/herrernst/31b75f42bc12acc7c8be70de01ea237a/raw/4d3456711b90c107d9d52619b0bb0305440d905d/index.html

Does anybody know why this is happening? I've noticed the same behavior with another font, so it's probably not specific to this one. Thanks.

[frankrolf]

It’s a general difference – I think you’ll be able to observe rasterization differences in most fonts that come in both TTF and OTF flavors.
It also depends on the OS, browser used, screen, and other factors.
Here are four screenshots from Safari and Chrome, on hi- vs lo-DPI screens.

[herrernst]

On your screenshots from macOS, I see no difference between OTF and TTF. I know font rendering is different between OSes and browsers and low/hi-DPI, but I'm surprised there's such a huge difference between OTF and TTF on the same platform.

[frankrolf]

OTF and TTF use different hinting methods, so some degree of visual difference is expected.
Note that you can also fine-tune the “darkness” of type on Windows, however I’m not sure how different font formats will be affected.
Probably you’re already aware of this site, which may help in understanding some of the differences:
http://rastertragedy.com/RTRCh0.htm

[herrernst]

Thanks for the link.