Multiplier Image Specs

Quick question I'm sure others will have/have had:

When choosing to add multipliers, and one creates separate Image Styles for each of those multipliers (1.5x, 2x), what are the file sizes and resolutions in order for them to still be rendered the same size as the original 1x yet higher resolution?

Example: If I have an image that is 100 pixels wide at 72ppi. For 1.5x that would be 150 pixels at what 108ppi? For 2x that would be 200pixels at 144dpi? If that's the case, how can one use Image Styles to change resolution? I'm not seeing that option. It could be as easy as the software automatically resizing the 200pixel down to 100pixel width.

These Image Styles in D7 don't have a resolution field: Adaptive, Define canvas, Change file format, Focus Scale and Crop, Resize, Scale, Scale and Crop, etc.

Could anyone shed some light on this for me?

SOLUTION

I googled about retina images and those sources say the images are not a higher pixel per inch count, just double the size, so a 100pixel wide original at 72ppi would need a 200pixel wide 72ppi retina-ready image. I've solved my own question but maybe keeping this in the issue queue will help others.