Channel Packer is an Unity Editor Extension that allows you to pack up to 4 different images in one texture, to manage and process them at the same time, saving memory.

It can be used for different packing modes and has options that allows you to use colors instead of textures, invert the textures, select the desired input channel, etc.

Furthermore, can be used for single packing – just to make a quick packing, or in batch mode – working on multiple textures sequentially.

Here there is the full documentation and some images: