Re: A follow-up on my post

Hi everyone,

Brian Lawler's color management problem may become normal for  
ColorSync users. The rich black result is exactly what Apple expects.  
Icefields 4.1 operates in the same way, and it uses ColorSync and OS  
10.5 as described by developer.apple.com. ColorSync is a color space  
to color space transformation method. It does not pass through  
PostScript's device spaces. (See http://developer.apple.com/technotes/tn/tn2035.html 
 for a diagram of this procedure.)

Here is one scheme that may happen:

The PDF encodes black as: MyriadPro 0.0/0.0/0.0/1.0, and uses  
DeviceCMYK and CMYK setcolor

The PDF page may be rasterized to halftone using a method similar to  
OS 10.5 Core Graphics:
CGContextDrawPDFPage(pdfCGContextRef, page);

During the OS 10.5 rasterization process, device colors are encoded in  
color space (I guess the Generic CMYK model) and then a color space  
conversion to the output color space occurs. There isn't an Apple  
CGPDF or PDF Kit function available to obtain the embedded profile(s).  
In a PostScript workflow the output color space is coded as an CSA.

If the output ICC profile is kCGColorSpaceGenericCMYK, then Icefields  
converts black to 0.79/0.73/0.68/0.68 resulting in rich black. In Mr.  
Lawlers case, the output ICC profile is embedded in the PDF and the  
RIP appropriately uses that profile.

The only color space conversion method that would be successful at  
maintaining 1.0 K is a profile with a black generation curve defining  
100 % black as 0.0/0.0/0.0/1.0. Does any profile do this?

Icefields 4.1 displays the result of color space conversions, scaling  
to the halftone resolution, and halftoning. It's a good thing to have  
Icefields :-)

Stephen Herron
stephen.herron@xxxxxxxxxxxxxxx



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