Soft Shadows and Color Shift

[Steve Mills]

On Nov 20, 2007, at 08:29:36, Rob Briggs wrote:

> A few weeks ago I had a problem with 100% cyan showing up with a  
> black screen on my RIP.
> Jay with Multi-Ad called and said it could be a preference for  
> "convert RGB to CMYK".
> When I unchecked this pref everything was fine.
> However he also told me he has seen this same problem on ads  
> containing soft shadows.
> Unfortunately we have seen this problem now too.
> We just printed a red & green Christmas section.
> To simplfy things we use the cyan plate for the spot green and the  
> magenta plate for the spot red.
> All of the ads that have soft shadows had a color shift putting  
> black and magenta into the cyan elements.
> There was also a black screen put into the magenta.
> Needless to say, we now have a red and muddy-grayish-brown Christmas  
> section.
> Is there anything I can do to avoid this other than just not using  
> soft shadows (which by the way is the only reason we upgraded to 8.0).

What Creator has to do to render soft shadows to PostScript (or pdf)  
is to create a bitmap of the shadow and everything behind it. This  
bitmap is rgb. But since the other colors are most likely cmyk, it has  
to convert everything to rgb (and then back), otherwise the originally- 
cmyk colors in the rgb bitmap would not match the cmyk colors where  
the soft shadow bitmap overlaps other elements.

You could work around it by creating your own images of areas  
containing soft shadows and the elements behind them, then use those  
in place of the actual shadow. But again, you'll probably run into  
color shifts because of the required color space conversion.

We're working hard to fix this in the future.

_________________________________________________________
Steve Mills                              Me: 952-401-6255
Senior Software Architect                         MultiAd
smills at multiad.com                       www.multi-ad.com