Scaling raw PNG in Nine Patch way before saving as Nine Patch image

I have got PSD file from graphic designer. There is a big image 1400px x 1000px (text area background). Image is light at the top and dark at the bottom (vertical color gradient). Left and right side are the same (no horizontal color gradient).

Standard 9-patch tools(editors) enables export from xxhdpi to ldpi (reduces the size). It's not exactly what I am looking for.

I found one tool which finds repeating area in raw PNG and offers to reduce 9-patch to 100px x 1000px.

But I would like to go further and also reduce vertical image size. There is just a gradient in vertical direction. Which tool enables me scale repeating area just before saving it as nine patch? I want hdpi nine-patch is 100px x 160px which I will use then for creating ldpi nine-patch.

Actually I need to create nine-patch in opposite way. I have big png text box and i need to get nine-patch of it.