I make a low poly character in maya. Then I import into zbrush and make high poly sculpt and generate normal map. I apply the normal map to the low res model in maya and Unity and everything looks good. Then I take UV snapshot into photoshop and make my color texture. If I then create a normal map from my color texture I have 2 normal maps (1 from zbrush and 1 from photoshop). Is there a way to either combine the normal maps or use both? How does everybody deal with this problem. I’m kind of new to sculpting programs so I never dealt with this problem before. Thanks
What are you trying to achieve with this step?
Don’t you create a normal map from your color texture in photoshop? If not then the color texture just looks lifeless and flat. And if I don’t use the normal map created from zbrush then the low poly model LOOKS low poly. What is your workflow?
I’m not an expert on this, but I don’t see a reason for generating the second normal map. Why can’t you just use the normal map from Zbrush, as a normal map, and use what you paint in Photoshop as the standard texture map? It sounds like you’re adding in an unnecessary step, to me.
Because I like to add bullet holes, decals, scrapes and stuff in photoshop. Maybe I should just get used to adding all that stuff with alphas in zbrush. I dont know if you’ve ever used zbrush before, but the less time I spend in there the better. Zbrush UI and navigation is a disgrace.
Actually I just found this tutorial which describes the solution to my question. The author describes it better than I ever could http://www.poopinmymouth.com/tutorial/normal_workflow_3.htm
Don’t worry, it’s not a nasty sex site 
Yeah, I’m familiar with that site. That artist is really good, and is on these forums sometimes. And I disagree with you about Zbrush. I think it’s really fun to use!
If you need to do this in OS X (without Windows), I have a set of techniques and a command line script to combine normal maps and normalize it…I mostly use it for deriving large scale data from photos for normal maps (for example, making large scale rock faces from a 2D photo) and then combining the large scale data with fine grained detail.
Just remember that when you combine multiple normal maps in PS, the blue channel will get screwed up, so you either need to use the NVidia tool (Win) or NormalizePNG (Mac) to fix this, or your normal maps will not light correctly.
Tutorial for deriving large scale normal map data from photos:
http://www.cgtextures.com/content.php?action=tutorial&name=normalmap
Mac OS X normal mapping tools download:
http://digitalnightmares.dnsalias.com/Archives/Normal_mapping_tools_Mac.zip
NormalizePNG useage:
NormalizePNG path_to_inputfile/inputfilename.png path_to_outputfile/outputfilename.png
I have found the easiest way to use this is to drag/drop the NormalizePNG app to the command line, hit space, then drag/drop the input file, space again, and drag/drop the input file again, then change the name of the last file to avoid overwriting the original file.
On that note, if someone here was to take this script and wrap it into a simple GUI (where you could specify the input file and output file, with a button to click to execute)…well, that would rock.
Thanks for the links 
No problem, always glad to help another artist