Transition between two image textures on same mesh

I have a simple plane mesh object. I gave it two materials, each one is an image texture. I can combine them with a mix shader to see both textures, semi-transparent together. But what I want to do is to have one part of the plane be 100% of one image texture, and another part 100% of the other image texture, and have a smooth transition from one to the other over the middle area of the mesh. I think some kind of a gradient mask might work, but I’m not sure how to do that, or if there’s a better way.

Hi bill2reg,

Here is the solution for one of the cases:

I figured it out by myself. My solution is almost the same as yours. But thank you.