Fix rendering issue on tiffscaled devices

The tiffscaled contone devices have to be able to change their color model
to allow a more flexible use of the post render ICC profile with the output
intent. Prior to this commit, certain profile combinations would result in
mis-rendered results.

With this fix, if we are wanting to render to a CMYK intermediate
output intent but we want the output to be in sRGB then we need to use
-sDEVICE=tiffscaled24 -dUsePDFX3Profile -sOutputICCProfile=default_cmyk.icc
-sPostRenderProfile=srgb.icc .  This should then render to a temporary
buffer the is in the OutputIntent color space and then be converted to
sRGB.  This should look like the result we get when we go out to the
tiffscaled32 device. This is in contrast to the command line
sDEVICE=tiffscaled24 -dUsePDFX3Profile -sPostRenderProfile=srgb.icc which would
end up using the output intent as a proofing profile.  The results may be similar
but not exact as overprint and spot colors would not appear correctly due to the
additive color model during rendering.

1 files changed, 2 insertions, 0 deletions

diff --git a/base/gsicc.h b/base/gsicc.h
index 567417051..ed3398acb 100644
--- a/base/gsicc.h
+++ b/base/gsicc.h
@@ -33,4 +33,6 @@ extern  int     gs_cspace_build_ICC( gs_color_space **   ppcspace,
 extern const gs_color_space_type gs_color_space_type_ICC;
 extern cs_proc_remap_color(gx_remap_ICC_imagelab);
 
+int gx_change_color_model(gx_device *dev, int num_comps, int bit_depth);
+
 #endif /* gsicc_INCLUDED */