I use blender (for modeling and animation), Daz3d (for human figures and the large content library) and of course Photoshop. I'm still in need of a good tool f

I use blender (for modeling and animation), Daz3d (for human figures and the large content library) and of course Photoshop. I'm still in need of a good tool for combining multiple .tga frames into a single sprite sheet. It takes too long to do the task in Photoshop (load into a stack, change canvas size, distribute layers, resize) and I can't preview the animation until it's saved and built in the game engine. Any suggestions for a tool (free or paid) that would help stitch multiple frames into a sprite sheet?