I imagine one could use the Curves adjustment tool and/or the Shadows/Highlights tool after converting to B&W until Adobe can get a proper B&W tool like in Photoshop. It does seem kind of odd they skimped on that compared to some of the other tools (like Curves).
no i mean the color channel filters like in photoshop or lightroom or even filterstorm
Ahh, you mean like the Channels panel?
The short answer is: You can't, at least not right now. Your best bet right now is what I noted before.
Without a Channel mixer one can't call it B&W conversion I shall not buy the app for iPad
thank you for your answer