Seeking clarity in Retina iMac desktop images
I'll admit it: I'm a desktop image (nee wallpaper) addict. I love to use a wide variety of images, and change them often throughout the day, just to keep my work environment fresh. On my two external displays, I use iPhoto images—general photos on one, kid pictures on the other. But for the main iMac screen, I prefer to use photos taken by others—typically stunning landscapes and cityscapes from all over the world.
With the arrival of my 5K iMac, however, my existing collection was no longer sufficient. Yes, they were all 2560x1440 images, which matches the "apparent" resolution of the Retina iMac. But in order to make that image fill the Retina iMac's screen, it's first scaled up to 5120x2880, then displayed by OS X at 2560x1440. As a result, my desktop images aren't nearly as sharp looking as they were on my old 27" iMac's display.
As an example, here's a segment of two versions (2560x1440 and 5120x2880) of the Sydney Skyline, as screen-captured when set as my Retina iMac's desktop picture. As you move the divider bar right, you're revealing more of the 2560px version; move it left, and the 5120px version takes over.
After scrolling back and forth a bit, you might be thinking these pictures are identical, and I'm just seeing things. While I may be seeing things, the pictures are not identical. (Compare some closely-spaced lights and the crispness of vertical lines in each image to spot the differences.)
Read on for a closer look at the image, which really shows what you're losing by using a 2560x1440px desktop image on a Retina Mac…as well as a list of places I've found that have 5120x2880px images available.