Help Finding The Right Heightmapping Software for A Project

[LordIndy]

Ok I'm new here and didn't post an introduction, so "hi all" . Haven't lurked alot either in recent years, but I'm running short on project time so I've decided to just be forward and make this post and defer to those more knowledgeable than myself on mapping projects.

In short, Ive spent about two weeks experimenting with more programs than I can count but have been unable to find one that does what I need. In fact most terrain/heightmap programs seem to be entirely randomized based on fractal algorithms.

The Project:
I have a high-res 2d map (~13,966 x 6,773 pix; 1pix=1.86km2) with continental outlines based on realistic tectonic maps for a fictitious planet about 62% size of earth. I have an idea of where mountain ranges and lowlands (etc) need to be based on the tectonic activity and geological history, but I do not have any sort of detailed contours or such. I need to take this map and create a detailed (psudo-realistic) heightmap, however I don't have years to manually paint a heightmap in a raster graphics program or a 3d terrain program. So I'm looking for a program that I can create heightmaps and/or terrain to be exported as a heightmap, but it needs to be somewhere between random generation and the time intensive terrain painting tools. Specifically I'm looking for something where I can do something similar to lasso-selecting a region, choose to preform some sort of terrain modification like raise terrain or even add a mountain range, and have the program do most of the work through falloff calculations and such, so I only have to spend limited time refining later or automatically refine through some erosion algorithms or something.

What I need in my software of choice:
1) Import 2D raster image for use as a guide for further terrain editing
2) Assign heights using a area select / lasso-select tool
3) Export as heightmap or 3D terrain file
4) Not require using fine-scale paint tools for a ton of work
5) Create a decent looking heightmap or a heightmap that I can erode, filter, etc in another program for a realistic result.

> Maybe this program exists, maybe it doesn't.
> Maybe someone whose more familiar with Photoshop or Gimp has a technique they can share?
> Maybe there's a terrain program that can produce a generalized heightmap for me, and then use another program that can do the detailing to the heightmap?
> I'm open to pretty much any potential solution that is faster than manually painting an entire planet lol.

Thanks for your consideration and time!