Regarding DBFZ images
I hope I don't sound rude. I appreciate the effort put into adding transparency to DBS Broly and Bardock images, but unless you can make them as clean as Johhny's works, I don't think it's worth sweating over. It takes way too much work and image clarity is more important than transparency Imo.
Hey, Johhny here, sorry it took so long. For Xrd, I used this guide: https://mugenguild.com/forum/topics/generating-2d-guilty-gear-xrd-sprites-170997.0.html
This mostly holds up, but Rev introduced lighting effects that changes how the character looks in every stage, and the stage the guide uses has added effects in Rev that make it not work quite as nice. I personally used the Assassin stage since it has the characters look their default palette and has a lot of black.
for GranBlue, you might be able to do the same if the files are any similar to GGXrd. I've tried, but I couldn't get DBFZ to work for me, but maybe you might.
Hope this helps.