[argyllcms] Re: Perceptual intent black problems

Attached the screenshot.

On Fri, May 30, 2008 at 3:24 PM, Mihai Zahorski <zmihai@xxxxxxxxx> wrote:

> 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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