Aliasing for icon image

Hello

Running Kodi 19 on Window10.
It can see this aliasing in my custom icon images. (Captured in full screen of Kodi)


This original image is like this 

240X240x32b

Here is xml code display on Kodi skin.

<control type="grouplist">

...

<control type="button" id="1630">

                <width>60</width>

                <height>60</height>

                <texturefocus colordiffuse="$VAR[BackColorButton]">special://skin/media/new_video_osd/back_osd.png</texturefocus>

                <texturenofocus colordiffuse="$VAR[ColorIcons]">special://skin/media/new_video_osd/back_osd.png</texturenofocus>

                <onclick>back</onclick>

</control>

I want to know why aliasing is displayed on the icon.