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Re: Ghostscript pickling settransfer

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In article <39699421-a83d-4b05-bb61-c7730d7d2d02@googlegroups.com>, 
jdawiseman@gmail.com says...
> 
> As is typical on comp.lang.postscript, the answer is expert and quick. 
> 
> So it can't be done in PostScript.
> 
> > Possibly you could redefine setcolor, setgray, 
> > setrgbcolor, setcmykcolor, sethsbcolor. 
> Wouldn't work if the user of my code has bind'd the passed code parameters.
> 
> But it is strange that Distiller copes, even if the standard says it shouldn't. Perhaps Ghostscript is being more royalist than the King.

Not really. As I intimateed, its a difficult problem to see an answer 
to, especially when the colour spaces are not device spaces (ordinarily 
transfer funxtions can only be applied to device spaces, when 
rendering).

Device spaces are relatively easy to deal with, though if you had a 
colour transfer for a different space it would likely be difficult to 
apply it (what does it mean to apply a CMYK 4 channel transfer function 
to an RGB 3 channel space ? Which CMYK channel maps to which RGB channel 
?)

Separation and DeviceN spaces are, perhaps surprisingly, easy. At least 
for a single transfer function. They could be handled by applying the 
transfer function to each channel when the colour is specified, and 
altering the tint transform to incorporate the transfer into the device 
space tint transformation. However the same problem with colour transfer 
functions applies here as well.

I'm unsure how one would go about applying even a simple gray ramp 
transfer function to a complex space such as a CIEBased space (eg Lab) 
without converting the space into a device space.

I'm inclined to feel that applying transfer functions is likely to lead 
to odd results, but I would have to try it out with Distiller to see 
exactly what its doing with the more complex cases.

Because transfer functions are spcified as working in device space, 
applying them to something that *isn't* a device space is fraught with 
problems.

The whole original point of a transfer function was that it was device-
specific, so you could strip it out and replace it with a new one if you 
went to a different devioe.

Possibly we could come up with a means to implement this, yes, but it 
would be a new feature and would have to be done in the kernal code 
where we currently do colour space trnsformations. Its probably not 
impossible, but it *is* a lot of work.

And all because some PDF consumers can't correctly handle the existence 
of a transfer function......


		Ken

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Thread

Ghostscript pickling settransfer jdaw1 <jdawiseman@gmail.com> - 2015-04-14 14:01 -0700
  Re: Ghostscript pickling settransfer ken <ken@spamcop.net> - 2015-04-15 08:15 +0100
    Re: Ghostscript pickling settransfer jdaw1 <jdawiseman@gmail.com> - 2015-04-15 01:45 -0700
      Re: Ghostscript pickling settransfer ken <ken@spamcop.net> - 2015-04-15 10:04 +0100
        Re: Ghostscript pickling settransfer jdaw1 <jdawiseman@gmail.com> - 2015-04-17 01:35 -0700
          Re: Ghostscript pickling settransfer ken <ken@spamcop.net> - 2015-04-17 10:07 +0100
            Re: Ghostscript pickling settransfer jdaw1 <jdawiseman@gmail.com> - 2015-04-18 02:01 -0700
              Re: Ghostscript pickling settransfer ken <ken@spamcop.net> - 2015-04-18 11:23 +0100
                Re: Ghostscript pickling settransfer jdaw1 <jdawiseman@gmail.com> - 2015-04-25 15:06 -0700
                Re: Ghostscript pickling settransfer jdaw1 <jdawiseman@gmail.com> - 2015-05-15 06:37 -0700
                Re: Ghostscript pickling settransfer ken <ken@spamcop.net> - 2015-05-15 15:37 +0100
                Re: Ghostscript pickling settransfer Carlos <angus@quovadis.com.ar> - 2015-05-15 19:45 +0200
                Re: Ghostscript pickling settransfer ken <ken@spamcop.net> - 2015-05-16 09:03 +0100

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