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: Terence Wyse <email@hidden>
- Date: Thu, 29 Apr 2010 08:13:57 -0400
Joseph, what I think you've got (the 140 patch TIFF file) is a *linearization* or calibration file, not a file for creating a *profile*. In any case, as others have explained, you've got *device* values (CMYK) but no Lab values. The Lab values is something that needs to be discovered from printing a profiling chart.
There wouldn't be Lab values associated with a linearization/calibration file as the behavior of the device is unknown. In simplest terms, you print the linearization file, measure it using something like an EyeOne Pro or similar (maybe even a densitometer) and then that data gets fed into their software. At that point, the software has some sort of expected "linear" behavior for your device and does a basic curve adjustment to bring the device into conformance with that expected behavior. Linearization is rarely done using Lab values (although it can be) but is typically done using density values or "dot gain" via density and a dot area formula (Murray-Davies typically).
Once the device has been calibrated/linearized, it's usually at that point that you would print a proper *profiling* testchart that, once again, is simply a chart of CMYK device values (these charts are typically >900 patches, not 140 patches). The profiling chart is then measured to get the Lab values and then an ICC profile is made from this "characterization". There's still no EXPECTED or reference Lab values at this point, they sort of are-what-they-are but that information can be used by the color management "engine" or module in your device's software or driver. Again, as others have explained, this device characterization/profile is then used to help carry out the conversion between the device's current behavior (destination profile) and some expected or "reference" behavior (source profile). When it comes to profiles, it takes "two to tango" as a single profile in isolation really does nothing...it's only when it's paired up with another profile that the behavior of a device, in your case a printer, can actually be altered.
Clear as mud? :-)
Regards,
Terry
______________________________________
Terence Wyse, WyseConsul
Color Management Consulting
G7 Certified Expert
FIRST Level II Implementation Specialist
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