RE: Acrobat 8 Color questions
RE: Acrobat 8 Color questions
- Subject: RE: Acrobat 8 Color questions
- From: "Peter MacLeod" <email@hidden>
- Date: Tue, 26 Jun 2007 12:15:23 -0700
- Thread-topic: Acrobat 8 Color questions
> -----Original Message-----
> From: email@hidden [mailto:email@hidden]
> Sent: Tuesday, June 26, 2007 11:32 AM
> To: Peter MacLeod
> Cc: email@hidden
> Subject: Re: Acrobat 8 Color questions
>
>
> On Jun 26, 2007, at 12:08 PM, Peter MacLeod wrote:
>
> > RI is a graphics state attribute, meaning that there is an
> operator in
> > a content stream that can change the current RI. The
> initial graphics
> >
> > state is defined to be Relative Colorimetric by the PDF Spec. That
> > means
> >
> > that once a PDF is created, the rendering intent is fully
> defined for
> > each object.
> >
> > Some applications allow you to specify the rendering intent on a
> > per-object basis. Those are usually reflected in a PDF
> content stream
> > as a graphics state save operator, followed by the rendering
> > intent-changing operator, followed by the operator that draws the
> > object, followed by a graphics state restore operator.
>
> You lost me.
Sorry--there's a reason I'm not a technical writer ;-)
I think maybe it's sufficient to say, without getting into the details
of how PDF works, that the rendering intent is "known" for every object
within the PDF file. Application preferences for rendering intent
usually control what happens when you import or color convert an object
such as an image that's not part of a PDF or EPS file, i.e. that doesn't
have an implicit rendering intent. But the point is that a PDF file
*always* has a rendering intent defined for every object, because the
default is always Relative Colorimetric. There's no way in a PDF to say
"use the application's setting as the default instead" given how the
PDF spec is written. Sometimes it's useful to override what the PDF
specifies,
and that's possible in the Preflight fixups, etc.
>
> > I think the documentation you cited confuses "device-independent"
> > with "calibrated." A device-independent space like CIEXYZ is
> > colorimetric by definition. When we say color in a colorspace is
> > "calibrated" that means we know how to interpret device-dependent
> > values (RGB, CMYK, Gray, etc.) colorimetrically, i.e.
> convert them to
> > CIEXYZ or CIELAB, because the color is tagged with a profile that
> > tells us how to make that conversion. An ICCBased CMYK
> space is both
> > device-dependent and calibrated.
> > The documentation you cited talks about CalRGB being a
> > "device-independent"
> > color space, and I don't think that's an accurate description.
>
> Well, then is "Calibrated" tagged and "Device" untagged?
Yes.
--Peter
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