ZeroSprites is a CSS sprites generator aimed at area minimization using algorithms used in the field of VLSI floorplanning.
https://zerosprites.github.io/

Usage:
sprites.sh padding (directory | png files)
Output consists of sprites.txt and sprites.png

Notice:
Use pngnq to generate png8 output if necessary.
You can use png optimizer(optipng, pngout) to make output smaller.

Reference:
T.-C. Chen and Y.-W. Chang, ``Modern Floorplanning Based on B*-trees and Fast Simulated Annealing", IEEE Trans. Computer-Aided Design of Integrated Circuits and Systems (TCAD), Vol. 25, No. 4, pp. 637--650, April 2006.
Korf R. and Huang E., ``Optimal rectangle packing: an absolute placement approach", Journal of Artificial Intelligence Research, Vol. 46, P. 47-87, 2012.