Bape :
So then does scaling lower the resolution the monitor is showing? Most people and the user above are saying it does not reduce the PPI or lower the resolution..
It doesn't lower PPI per se, but can result in images being blurrier as if PPI were lowered.
Currently using a 24in UHD monitor, so in my case when I am using it with a 200-250% scaling, is the monitor showing at 3840x2160 still or has it been lowered down pretty much to 1920x1080?
The monitor is still displaying 3840x2160. At 200% scaling, everything (well, everything that scales) has been enlarged so it's the same size as if the monitor were 1920x1080, but it's still showing 3840x2160 pixels of information.
■ On apps which scale properly, the fonts have been properly scaled. So a font 10 pixels high with a 135 ppi 1080p screen becomes a 20 pixel high font with a 270 ppi 2160p screen. The font appears the same physical size on the screen, it's just sharper because its edges are defined by 4x as many pixels. It also enjoys the benefit of subpixel rendering.
https://www.grc.com/ctwhat.htm
■ On apps which scale but not properly, Windows has simply done interpolated resampling (usually bicubic). This results in larger fonts and GUI elements, but they're just scaled up in size and smoothed so they don't look so jagged. The price is that they're blurrier than proper scaling, especially if the scaling is not an integer multiple (200%, 300%, etc). No subpixel rendering either, making it look much blurrier than just the resampling would get you. This is why some fonts and dialog boxes from old apps look blurry in Windows 8/10.
https://blog.codinghorror.com/the-myth-of-infinite-detail-bilinear-vs-bicubic/
■ On apps which don't scale, everything is now half the size (1/4 the area). You've taken the app as it would display on the 1080p screen, and shrunken it down so it covers the same number of pixels on theo 2160p screen. Photoshop's menus are a good example of this - too tiny to be usable except on a huge 32-40 inch 2160p screen.
OS X has an easier time of this because the Mac was designed from the get-go to have scalable screen fonts. The entire design premise was that the monitor you plug into the Mac would tell the OS its physical screen size. The OS would do the math based on that size and the screen resolution, and figure out how much to scale the fonts to keep a 10 point font on the screen the exact same size as a 10 point font printed on paper. This is why Macs are wildly popular in the publishing and graphics industry. Apple had to come up with several font-scaling technologies to accomplish this (building on what they learned creating Postscript - font scaling for laser printers).
Windows wasn't designed this way. It was originally designed with bitmapped fonts. Scaled fonts were added later, but no thought was ever given to maintaining font size consistency based on physical monitor size and resolution. A 10 point font on a 1024x768 13" monitor was a different physical size than a 10 point font on a 1024x768 14" monitor. Until now. Consequently they're having to add in new function calls which allow fonts and GUI elements to scale properly, except older apps don't use those new function calls so they have to use kludgy resampling. And if the app doesn't even use the basic Windows API to draw menus, and instead draws them on their own (like the Adobe apps), the app doesn't scale at all.
Edit: One advantage of the Windows method is because fonts are fixed in size relative to the pixel grid, you can do subpixel rendering. OS X can't do this because every font is infinitely scalable; the best it can do is anti-aliasing. You can see this if you plug a Mac and a PC into the same low-res monitor - the OS X fonts look like crap compared to the sharp Windows fonts. Apple opted for accuracy over clarity (for subpixel rendering to work, the font placement has to be shifted slightly left or right to align it with the subpixel grid, which is unacceptable for page layout artists). This gave Windows an edge in font clarity when monitors were low-PPI. But now that high-PPI monitors are becoming affordable, the table is tilting the other way. Clarity is becoming a non-issue, while ease of scaling is.
Incidentally, the situation is reversed with Android and iOS. Android is designed to scale with screen size. iOS is not (which is why Apple has been forced to stick with doubling the screen resolution of the iPhone). I'm not sure why Apple made this design blunder, considering how successful font and UI scaling was for them on the Macs.
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