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 10:08:18 -0700
- Thread-topic: Acrobat 8 Color questions
> -----Original Message-----
> From: email@hidden [mailto:email@hidden]
> Sent: Tuesday, June 26, 2007 9:42 AM
> To: email@hidden
> Cc: Peter MacLeod
> Subject: Re: Acrobat 8 Color questions
>
> >> From: Rich Apollo <email@hidden> In Acrobat 8's Color
> >> Settings why is there no place to set a rendering intent?
> Is there no
> >> way to specify a rendering intent for the conversion of a
> document?
> >> What rendering intent gets used and how is that determined?
> >
> > PDF files have a rendering intent as part of the file
> specification.
> > In other words, there is never any question as to what rendering
> > intent a particular object should use, because the PDF
> graphics state
> > has a rendering intent, and its default is Relative
> Colorimetric. You
> > can override the rendering intent on a single-object conversion by
> > using the touchup object tool, then right-click and go to the
> > properties panel and select the "color" tab. The rendering
> intent of
> > the object selected is reflected in the panel, and you can
> change it
> > before clicking "Convert Colors."
>
> So, is the RI dependent on the Color Settings of the
> application that created the PDF? The PDF has an embedded RI
> and every object within the PDF has an embedded RI? So, if
> you repurpose a PDF, which RI gets used? Is Relative
> Colorimetric the default for the PDF specification, or is it
> the default because that is the default of the North American
> Prepress color settings file? And is Preflight the only way
> to view the RI for the PDF document?
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.
If you pick an object with the touchup object tool and select the color
tab in the properties menu, the rendering intent popup is set to the
current
rendering intent of the object.
>
[...]
>
> I was paraphrasing. I understand "device-independent" and
> "device- specific" color. It's Calibrated and Device that I
> don't grasp. Let me try again.
>
> From the help menu I'm getting that
> "Device" colors refer to untagged elements, and "Calibrated"
> refers to elements tagged with profiles of device-independent
> color spaces.
> So, "Calibrated
> CMYK" should be an impossibility, right, as CMYK is always
> device- specific? So, would elements tagged with profiles of
> device-specific color spaces fall into a third category that
> doesn't get displayed in the Convert Colors dialog?
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.
--Peter
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