Re: Finding CIELab Values from Target Chart TIF
Re: Finding CIELab Values from Target Chart TIF
- Subject: Re: Finding CIELab Values from Target Chart TIF
- From: Peter Skarpetis <email@hidden>
- Date: Thu, 29 Apr 2010 13:03:41 +1000
On 29/04/2010, at 12:42:55PM, Roger Breton wrote:
> Joseph,
>
> May I ask what makes you think that this TIFF file as an absolute set of
> "Reference CIELab values"? I could be wrong but, to my knowledge, these
> charts never have an a-priori set of associated CIELab values.
>
i was only mentioning it for the sake of completeness. I am aware that they would be in the colourspace of the process you are trying to calibrate.
Peter
> Best / Roger
>
>>
>>> Dear List
>>>
>>> I have a 140 Patch Target TIF file that I don't have access to the
>>> Reference CIELab values.
>>> The chart is used by PhaserMatch 4.0 (created by X-Rite for Xerox).
>>>
>>> Requests to both Xerox and X-Rite have not been fruitful and so I'm
>>> now wondering if their is a way to "extract" these values from the chart
>> itself.
>>>
>>> I have opened the the Chart TIF in Photoshop and can read the L*a*b*
>>> values in the Info palette - but only as single digit L*a*b* values.
>>> Is there a method to obtain more precise (minimum 3 decimal places)?
>>
>>
>> The Lab values you are seeing in photoshop are just a simulation. They are
>> calculated from the RGB / CMYK values in the tiff file using your current
>> colour settings. This is assuming that the TIFF file is not an Lab file.
>> If you wish to have more precision, use photoshop or any other image
>> viewing software to extract the RGB/CMYK values for the patches. You can
>> then use Colorsync utility or any other such tool to extract more precise
> Lab
>> values using CMYK/RGB profiles for the process you are trying to simulate.
>>
>>
>> Peter Skarpetis
>
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