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24-bit PNG - troubles adding an alpha

Posted: Tue Oct 12, 2010 6:39 pm
by rkwright
OK - I feel like I'm missing something. I have a 24-bit PNG that has a background value of 254,254,254 that needs to be made transparent.

I haven't had luck with any combination of the flags below (using nconvert 5.60):L

-ctype rgba
-add_alpha "value" (what is "value" supposed to represent? Can't find info in docs)
-merge_alpha
-transpcolor 254 254 254

Any thoughts on how to make an RGB png into an RGBA, with 254,254,254 having an alpha of 0?

I'd appreciate it.

Re: 24-bit PNG - troubles adding an alpha

Posted: Wed Oct 13, 2010 7:11 am
by xnview
rkwright wrote:-add_alpha "value" (what is "value" supposed to represent? Can't find info in docs)
value is the alpha that you want to add

Re: 24-bit PNG - troubles adding an alpha

Posted: Sat Mar 19, 2011 10:36 pm
by krawhitham
xnview wrote:
rkwright wrote:-add_alpha "value" (what is "value" supposed to represent? Can't find info in docs)
value is the alpha that you want to add

Code: Select all

nconvert.exe -out tga -add_alpha alpha.tga -overwrite main.tga
produces a 100% black alpha channel in main.tga

I'm I using the wrong command?

Re: 24-bit PNG - troubles adding an alpha

Posted: Sun Mar 20, 2011 8:47 am
by xnview
no -add_alpha 255