Windows batch file - width / height operations

[queensoft]

I use ImageMagick 6.8.2-8 2013-02-09 Q16 under Windows 7 x64 SP1 Ultimate.
I 'm trying to apply Perspective distort, but I need to use width / height coordinates.
This works OK:

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convert out_textured.jpg -alpha set -virtual-pixel transparent -distort Perspective 0,0,9,95,0,"%%h",0,"%%h","%%w","%%h","%%w","%%h","%%w",0,"%%w",0 out_pers.png

But this is what I need:

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convert out_textured.jpg -alpha set -virtual-pixel transparent -distort Perspective 0,0,9,95,0,"%%h",0,"%%h"-70,"%%w","%%h","%%w","%%h","%%w",0,"%%w",0 out_pers.png

The difference is height minus 70 pixels - "%%h"-70
I have tried these and they do not work:
"%%h"-70
"%%h-70"
""%%h"-70"
Please help. Thanks.

[snibgo]

You can do the calculation before the convert, eg:

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FOR /F "usebackq" %%L IN (`%IM%identify -format "WW=%%w\nHH=%%h\nHHm70=%%[fx:h-70]" %SRC%`) DO set %%L

then use %WW%, %HH% and %HHm70%

Or you can include %[fx:] within the distort:

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convert ^
  in.png ^
  -distort "0,0,9,95,0,"%%h",0,%%[fx:h-70],"%%w","%%h","%%w","%%h","%%w",0,"%%w",0" ^
  out.png

[queensoft]

Great, THANKS !!
Second one worked like a charm (with fx).
Thanks again !