Image size test page

Due to preliminary pixel density tests in the Image layout test page, I’ve been exporting my images assuming an @3x device pixel ratio and a moderately large screen (939 CSSpx height). My exported size has been 3756 × 2817 (landscape). However, this may have been overkill.

Image size overkill is important to consider because image size goes up with the square of pixel dimension saved.

Some rough device stats.

device px density CSS px physical* px
Yours (live) (need JavaScript enabled) (need JS enabled) (need JS enabled)
recent iPhones max 3 428 x 926 1284 x 2778
recent iPads max 2 1024 x 1366 2048 x 2732
monster MBP 2 1728 x 1117 3456 x 2234
my laptop 2 1680 x 1050 3360 x 2100 (implied), 2560 x 1600 (actual)

* "physical" isn't even right. If I change my display settings, the "pixel density" stays at 2, but the CSS pixels goes up. But clearly there are more physical pixels per CSS pixel if I choose a scaled screen resolution. Indeed, my physical display specs list 2560px width. So the `window.devicePixelRatio` is lying. I've seen super detailed articles about this but I think it's not worth diving into right now.

Thinking about my exports:

Testing two variants

3756 x 2817

2504 x 1878

Perceptually nearly identical. After cleaning my screen and glasses, and tabbing furiously between them about 40 times, I may have a slight preference for the lower resolution one. If I’m actually perceiving something real, it could be because it’s actually using the legit 2x pixel density rather than having to downsample from 3. So this is great news.

What about portrait photos? They’re displayed at 704 x 939, currently 2113 x 2817. It’s great that these already weigh 56% of the landscape ones. Factoring down to 2x desktop pixel ratio would mean 1408 x 1878. But what about portrait devices?

What about side-by-side photos that are naturally going to be displayed smaller?

So, iPads are a bit bigger. How do I do exports going forward?

Apple Photos has a “dimension” export, which I assume caps the larger one. So I could cap to

Leaning smaller for now given viewing issues. But gonna leave on the table for a sec and work on the other things.