These icons are generally located in the
<resolution> corresponds to each resolution available: for instance, 22x22 or 128x128.
You can see what icon resolutions are available for your particular program using this command:
find /usr/share/ -name <application>.png
<application> with the name of the executable for the program in question. This can be verified using the
$ which google-chrome
$ which chrome
For instance, these are the icons available for Chrome on my system (ran from
$ find . -name google-chrome.png
If you don't have high resolution versions of these icons, you could try an answer suggested here and simply create them with the GIMP image manipulator using
Image -> Scale. Then, place the new icons in the particular directories.
If high resolution versions are present here but you still see a pixelated image when you ALT + TAB, you can try the second answer from the previous link:
StartupWMClass=<application> to the application's .desktop file within the
So for this example using google-chrome, I would add