if you use point instead of linear sampling then your png's become distorted.in some images you will see that more since it has to do with colour combinations and thin lines.and thats why you think some images are ok and others arent.in matter of fact if you use point all pngs loose quality.
now using linear instead of point is the solution to your problem until things start to move.since pixel rounding "off" renders sub pixel instead of integer like "on", you start to have seams between tiled sprites.if you use "on",
seams disappear but you have a loss in smooth movement since it renders integer and becomes a little jerky plus you have loss in picture quality.
it is a $#@%$@#% situation especially for us that use spriter since we cannot use pixel rounding "on" because spriter renders subpixel and the tweening gets destroyed and on the same time we have seams using the tilemap plugin if we are at "no"!
so i had to revert to old school tilemaps as animation frames and it works in crome without seems and perfect picture quality until i export it with node webkit and it looks like swiss cheese between tiles again.
@ashley says that thats the way it is but i will fight until my last breath until he figures out a solution since i know he can(i have faith in him ) because most complex projects start to hit that wall between quality and seams.