It’s about ImageSet

The LR states ( Image_Set_Editor ):

All images must have the same aspect ratio. For example if your 1x image is 64x64 @ 72DPI, then the 2x image must be the same ratio (1:1) and would typically be 128x128 @ 72DPI or 64x64 @ 144DPI. Make sure that that the tool you use to create or edit your images properly sets the image DPI (dots per inch). Some tools (such as Photoshop) do not properly set the DPI which can cause Xojo to interpret the image as the wrong size.

People are confused nowaday about size and resolution.

Size is Width and Height
Resolution is a value in dpi.

Another problem comes from the application software developers: they displays the images at different resolution. For example, with PhotoShop, you can display the image at the correct resolution (64 x 64 @ 144 dpi will display an image of 64 x 64) or display all pixels.

MacOS Finder, when set an iage as a folder window background will display the image… strangely: the same size image will be draw at half its size if it have a 144 dpi resolution ! (with El Capitan)

What the LR imply is Confusion above Confusion (and if you run macOS, there is another Confusion layer).

this is just wrong
it should be
and would typically be 64x64 @ 72DPI or 128x128 @ 144DPI
since the DPI is higher its draws more densely, and therefore smaller, than things drawn at 72 DPI

the caution about some tools not setting or saving the DPI information in the image correctly is one I’ve seen

This is not my opinion.

An image that says its width and height is 64 x 64 have to be displayed in a 64 x 64 area; its dpi is not relevant there.

Now, I probably am an idiot to think that :frowning:

oh its very relevant

a 64 x 64 @72 dpi picture is that size when drawn
a 128 x 128 @ 144 dpi picture is ALSO the same size when drawn
a 192 x 192 @ 216 is also that size