XPost: misc.phone.mobile.iphone, alt.comp.os.windows-10   
   From: mariasophia@comprehension.com   
      
   To add value so that this becomes a useful reference for all three common   
   platforms, Android, iOS and Windows, here's a quick summary of details.   
      
   1. The universal 1x1 pixel solid-color privacy-aware method:   
   A mathematically perfect solid-color wallpaper only needs one pixel.   
   Every OS scales it losslessly because all pixels are identical.   
      
   Minimal PPM format (ASCII only):   
       P3 1 1 255 R G B   
   This produces a 1x1 pixel image with the exact RGB values you want.   
   It contains:   
    a. no EXIF   
    b. no metadata   
    c. no compression artifacts   
    d. no camera noise   
    e. no unique patterns   
    f. no fingerprintable entropy beyond the RGB value   
   This works on Windows, Android, and iOS/iPadOS.   
      
   2. Windows notes:   
   Windows supports solid colors natively, but the GUI color picker:   
    a. does not accept HEX directly   
    b. does not always allow precise RGB entry   
    c. may apply GPU dithering depending on settings   
      
   Using a generated PNG guarantees:   
    a. exact RGB   
    b. no dithering   
    c. no metadata   
    d. no artifacts   
   Windows accepts any PNG as wallpaper without modification.   
      
   3. Android notes:   
   Android is the most flexible platform.   
      
   Universally true:   
    a. Any app can set wallpaper via the public API.   
    b. Any image viewer can "Set as wallpaper".   
    c. A 1x1 PNG scales perfectly on all devices.   
      
   Not universal:   
    a. Native solid-color pickers vary by OEM.   
    b. Google Wallpapers app has a limited palette.   
   Yet, the offline PPM -> PNG method in this PSA works on all devices.   
      
   4. IOS/iPadOS notes:   
   iOS and iPadOS cannot generate a true solid color using the built-in   
   "Color" wallpaper option. Even when entering a HEX value, Apple applies   
   a gradient.   
      
   Limitations:   
    a. All "Color" wallpapers are gradients.   
    b. No API exists for apps to set wallpaper.   
    c. No toggle to disable shading.   
    d. No way to force a flat color through Accessibility.   
      
   Therefore:   
    a. The best way to get a true solid color is to import an image.   
      
   5. Privacy benefits of solid colors on the various platforms:   
      
   A. Android (modern versions) exposes only:   
      a. 3 main colors   
      b. 1 secondary color   
      c. 1 tertiary color   
      d. luminance metadata   
      
   B. A pure solid color collapses all of these to the same value, producing:   
      a. near-zero entropy   
      b. no unique fingerprint   
      c. no reconstructable image   
      
   iOS:   
    a. Apps cannot read wallpaper data unless the user gives them the image.   
      
   Windows:   
    a. Any program can read the wallpaper file, but a 1x1 PNG contains   
       nothing but three bytes of color.   
      
   6. Imagmagic command syntax:   
   This works on Windows, macOS, Linux, Android (via Termux), etc.   
   but I could find no native, user-installable version of ImageMagick for iOS   
   or iPadOS so only iOS can't do what all other operating systems easily do.   
    I. Create a solid-color PNG from a HEX value:   
       magick -size 1x1 xc:"#ABCDEF" solid-abcdef.png   
     II. Scale it to device resolution:   
       magick solid-abcdef.png -scale 2360x1640! ipad-2360x1640.png   
      
   7. How does pure solid black help with privacy?   
   Pure black (#000000) produces the lowest possible entropy on Android.   
   Every device returns the same WallpaperColors object.   
      
   Benefits:   
    a. hardest wallpaper to fingerprint   
    b. reduces OLED power consumption   
    c. visually clean and uniform   
      
   Note that while the gradient contains more entropy than pure black, on iOS,   
   apps cannot access it anyway, so the difference is irrelevant in practice.   
      
   Windows exposes the wallpaper file directly, so gradients absolutely   
   contain more fingerprintable data than pure black would.   
   --   
   If privacy is a million things to do, most people only know about three.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)