For those unfamiliar with HDR, it stands for High Dynamic Range. This is actually a photography technique that combines photos with different exposures to create a single photo that looks completely out of this world. That technique has been applied to video as well and in recent years we’ve seen seeing TVs with support for HDR.
With YouTube now supporting HDR on the iPhone, it means that iPhone X users will be able to enjoy those contrasty colors that Android users have been enjoying for a while now. At the moment it seems that this is only applicable to the iPhone X as far as iPhones are concerned. As MacRumors points out, the iPhone 8 and 8 Plus do support HDR but they are a different breed compared to the iPhone X’s Super Retina HDR, so the experience will be different if and when support does arrive.
In the meantime iPhone X users can probably keep an eye out for this new feature by launching the YouTube app.