[Desktop_printing] Update of the Printing Summit Agenda

Michael Sweet mike at easysw.com
Thu Jan 12 10:20:52 PST 2006

Ralph Giles wrote:
> On Wed, Jan 11, 2006 at 08:46:24PM -0500, Michael Sweet wrote:
>> The MaskDict entry in a Type 3 image defines the mask image, which
>> for InterleaveType 1 requires you to provide an alpha mask with the
>> same depth as the color data in the main image.  See pages 303 to
>> 307 of the PostScript Language Reference Manual, Third Edition.
> Yes, the mask component must be the same depth as the other components 
> for an even data interleave, but it is converted to 1 bit. See the 
> IterleaveType entry in Table 4.22, PRLM3 p.304:
> "The mask sample must have the same number of bits as each color 
> component of the image sample, with all bits set to the same value 
> (that is, either all 0 or all 1); any other value will be treated
> as if the bits were all 1."
> And the mask component is only 1 bit in all other defined 
> configurations.
>> (This *does* work, I use it in HTMLDOC's Level 3 output...)
> With Ghostscript? Are you sure this isn't just a binary mask?

Nope, not just a binary mask.  I tested using PNG files with full
alpha - some printers did a hard masking while others (our Xerox
printers IIRC) did a full alpha blend.  I don't remember what gs
did, but it still worked well enough for me to leave it in...

> In any case, it's not correct to say that PDF and PostScript have the 
> same graphics model. The addition of transparency groups and blend modes 
> are still a huge difference even if PostScript did support PNG-style 
> alpha masks.

True, however I rarely see any PDF files using those features, even
from Illustrator...

Michael Sweet, Easy Software Products           mike at easysw dot com
Internet Printing and Document Software          http://www.easysw.com

More information about the Printing-summit mailing list