Pixelated icon

Hello, I have a problem with the TabBar,
The display of icons is pixelated, I use the size of 25 * 25 for the normal display, 50 * 50 for @ 2x and 75 * 75 for @ 3x, before that I used the size 64 * 64, 128 * 128 and 256 * 256 but the result was not good.
Do you have any suggestions for me?


Thanks for your help :)
@antiguab 