Digital BW, The Print

> From: Roy Harrington <roy@...>
> Reply-To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
> Date: Fri, 21 Oct 2005 18:15:52 -0000
> To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
> Subject: [Digital BW] Re: ICC v. Transfer Function in Epson driver
> 
> 
> It's mostly a matter of semantics.

I was trying emphasise the point, particularly following a conversation with
Paul Roark, that when you have a colour managed workflow your workspace
doesn't matter because you convert to the print space at printing.  Of
course when sending stimulus data to the printer for profiling you want to
send the right file values (the values you think you are sending).  But once
profiled you needn't worry about this.  If you work up an image in GG2.2 and
then also in Lab so that they look exactly the same and print each with the
same properly made profile, then the two images will print exactly the same.

(Paul had asked whether editing in Gray Lab would change the shadow
compression he was witnessing.  Answer: no.  That is, exploring different
workspaces doesn't get you anywhere in a colour managed workflow.)




> 
> But I think there are a few absolutes.  To me a stepwedge labeled 100, 95,
> 90...
> better have the those numbers in the file.  If your 90 happens to have 94 in
> it
> you not longer have a stepwedge -- you ought not to sample values there.
> Your post mentioned various conversions of stepwedges -- this destroys the
> stepwedge  --  it's NOT a stepwedge.  I can't emphasize that enough.

Yes I was using the step wedge as an example of an "image".  I am talking
post profiling workflow.  You're talking profiling.

> 
> The important thing is that the K values are the actual numbers in the file,
> the
> L values are the meaning of the numbers given a specific profile.  A stepwedge
> ALWAYS has the same numbers,  ASSIGNing different profiles changes just the
> meaning and therefore what you see as L values.

Yes and when you send the file values for the profiling exercise nothing has
changed because Assign leaves the file values unchanged.  But if it were an
image for print, assigning a different profile will change the look of the
image and the print.

> 
> Your examples of converting files and find the same L values is just the
> definition
> of what Convert does -- it finds the new file number that will lead to the
> same
> L value.

Yes.  
> 
> -----------------
> 
> On a semi related issue, I looked at you PDF on Color Management.  You have
> basically a comparision of ABW vs QTR vs ICC.  The major point that is not
> mentioned is -- what's the profile attached to the stepwedge?  For the non-CM
> cases this is irrelevant but for the CM cases its crucial to the results.  The
> fact
> that a CM graph is different than a non-CM graph is natural since the goal is
> very different.  And you'd get a different CM graph for different grayspaces.
> 
> One way to look at this is that a non-CM stepwedge print is printing evenly
> spaced K values, but a CM print is printing L values that are spaced based on
> the grayspace.  

Yes.


>When you print a GG 2.2 wedge with CM what you are really
> telling the driver to do is print a wedge with L values 0,1,5,13,20,26, ...
> (these come from sampling L on a GG 2.2 wedge).
> 
> On the surface this may seem a picky technicality but it really is very
> different.

No - I understand.  In each case the file was untagged grey and so I believe
in each case the same file numbers were sent.