How have people come to the conclusion that displaying a low-information version of the image to be loaded as a placeholder results in a quicker perceived load? To me all these effects just look rubbish and distracting, with no benefit at all – certainly not the perception of speed. It's not like I can ever understand what the image really is before it's fully loaded anyway, with our without fancy placeholder.
Loading images as soon as they are within viewport is already too late. You want to load them before user gets there. So you could just not mess up with native browser loading in the first place. Because all those requests and client side calculations will add up.
When you have image heavy content please load an image when I'm one or two page heights before the image. This way when I get there it will already be there. You could then just use regular single background placeholders, because I (and I would believe that you also) never intend to see them in the first place.
