[argyllcms] Re: Perceptual intent black problems

You are right, I was just testing for perceptual, the problem is for
relative too, I'm sorry if my original question missled you.
I have played a little with xicclu and you can see how the neutral axis
looks in the attached image.
Since the printer I am trying to profile has three black inks I was
wondering if that doesn't complicate things for the black generation. This
is what led me to think that a function similar to neutralize would be
needed in Argyll since there I can get usable results with default settings.
The black inks have usually some sort of color in them, they are not 100%
gray, especially on this printer, this is why I was wondering if this is
taken into account or not. Any documentation about this part of the code
would certainly help me understand the process.

At this moment I do not have access to a printer with only one black ink to
support this, I will test next week and I will also let you know if the
output will be ok or not after managing to tame the black generation
settings.

Thank you.

On Fri, May 30, 2008 at 12:09 PM, Graeme Gill <graeme@xxxxxxxxxxxxx> wrote:

> Mihai Zahorski wrote:
>
>> I am trying to make a profile for Epson SP4800 ( Luster 300g paper ) and i
>> have big problems with printing shadows using perceptual intent.
>> I used Adobe1998 as source profile for gamut mapping and I loose details
>> in
>> the shadow areas because of the black generation.
>>
>
> If this is specific to perceptual, then I doubt it is due to black
> generation,
> since the separation will be common to all the intents in an ICC profile.
>
> I am attaching two screenshots of the test image displayed with the black
>> channel turned off :
>> -the first is one is using a profile generated with black limit 90
>> -the second one is using a profile generated with black limit 70.
>> The other parameters used are: 240 total ink limit, 0-100 black generation
>> with 0.5 shape ( I didn't want to 'hide' the black generation ).
>>
>
> Sorry, I'm not at all understanding what you are hoping to illustrate.
>
> For me it seems there is something wrong in the black generation, in how it
>> substracts the levels of CMY.
>>
>
> What leads you to think that ?
>
> How can I control better the black generation?
>> I only want a smooth curve that would not destroy the details.
>> Using Gretag ProfileMaker showed a much more moderate black generation
>> although I have used the same parameters. I also saw the following
>> controls
>> in the separation page: "Black width" and "Neutralize". Are there similar
>> functions in Argyll?
>>
>
> There is no equivalent currently to "width" in Argyll, the black generation
> is always "wide". You control the level of black using the -k parameters,
> as illustrated here <http://www.argyllcms.com/doc8/Scenarios.html#PP6>.
> This
> control is not as easy to use as perhaps it should be, and a number of runs
> using xicclu is generally require to arrive at a reasonable curve.
>
> It's hard to comment any more than this without the .ti3 file, and the
> parameters used to create the profile. Generally the black generation
> doesn't change the color at all (it's simply choosing between all the
> combinations of CMYK that can generate a particular color), but it
> affects secondary aspects, which can show up as color artifacts indirectly.
>
> Graeme Gill.
>
>

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