[Question] Struggling to make my own tileset

Hello!

I am new to Pokemon Essentials and although I am very excited to make my own pokemon game, I struggle a lot with Tilesets. So instead of using a premade one, I've started working on one of my own.
As far as I understand, I have to take 16x16 px tiles, place them on a grid that is 8 tiles wide, which makes 128 px, and once I am done, resize it to get a 256 px wide tileset and whatever px high.

However, I have a huge problem with this resizing part.
When I resize the tileset, I get weird light-grey pixels appearing all around the objects displayed. It surrounds each and everyone of them. So when I setup the transparency on RPG Maker, the white background becomes transparent, but not the light-grey pixels. So obviously, when I put let's say a tree in the game, it comes with a very thin white-grey edge.
(I'd like to show you but I can't post links for now since I have not made 5 posts yet)

I have tried many different resizing tools : Paint, Paint.net, Gimp and Photofiltre. I always get the same result : additional pixels appear and it would be too long to erase them one by one on each tile..

I've checked several tutorials and it's not an issue that I've seen so far.
Could you help me please ? :)

Ok so basically it looks like that:



What can I do? :(

I feel you may have resized then incorrectly.
A lot of modern image manipulation tools seems to blur, or distort images when resized.

I recommend just grabbing MS Paint XP (It works on windows 10)
and selecting your tiles, and then pressing CTRL and (num pad) +.
It will resize your selection pixel perfectly by double.

In GIMP the default interpolation method is CUBIC. You don't want that.
Select None as interpolation instead and everything will be fine.

Thank you! Both ways work perfectly.
You are right, there was a blurry effect.

Paint XP resizes it perfectly without any alteration :)
Same goes for Gimp, the Cubic thing was messing everything up. Gimp is a better tool overall so I'm gonna stick to it :)