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Author Topic: CTP shows some print profiles off axis. Why?  (Read 1466 times)

tvalleau

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CTP shows some print profiles off axis. Why?
« on: March 05, 2016, 09:39:00 pm »

Hi

I'd like to learn what I'm seeing, and what it means.

I use an i1Photo Pro 2 for calibrating my 10-bit monitor and making profiles for my papers.

Today I created a paper profile for Canson Platine, and one for Red River Ultra Pro Satin.

I dropped them both into Color Think Pro (CTP) just to have a look.

Here's what I see: the Platine profile's white & black point is right on the L axis.
The RRUPS white/black point is shifted off the L axis along the b axis, toward blue.

This is with CTP set to display "device gamut".  If I set that to Perceptual or Rel Col, the white/black points snap right to the L axis, and match the Platine profile.

Now, these profiles were made using identical settings, swatches, version type, and so on.

The question is why is the L-axis offset on one, but not the other, and only when viewing device gamut?

At this point, I'm wondering if it's that the RR paper has a lot of OBs, while the Canson doesn't, which might make it shift toward the blue when plotted against the device gamut... but I'm guessing.

If someone can educate me, I'm appreciate the knowledge.

Thanks.
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Doug Gray

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Re: CTP shows some print profiles off axis. Why?
« Reply #1 on: March 05, 2016, 10:04:12 pm »

Normal.

You are seeing the effect of OBs. Rel Col and Perceptual tracks the white point while device gamut tracks absolute color. OB's skew the white point. Device color's RGB value of (255,255,255) will be the paper white which is not a neutral color when lots of OBs are present. The neutral axis in device color is where a* and b* are zero and the printer has to use colored ink to counteract the OB's. This means that device RGB values have to be shifted into a neutral area and so are not on axis.
« Last Edit: March 05, 2016, 10:10:55 pm by Doug Gray »
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tvalleau

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Re: CTP shows some print profiles off axis. Why?
« Reply #2 on: March 05, 2016, 10:26:38 pm »

Excellent and clear reply. Thank you. (Also, nice to know I sorta figured it out myself  ;-)

Appreciate your time.
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JRSmit

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Re: CTP shows some print profiles off axis. Why?
« Reply #3 on: March 06, 2016, 07:08:46 am »

Can you add a screen shot? The white point shift to blue if oba's are present. But the black point not necessarely.
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Jan R. Smit

Doug Gray

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Re: CTP shows some print profiles off axis. Why?
« Reply #4 on: March 06, 2016, 11:18:46 am »

Can you add a screen shot? The white point shift to blue if oba's are present. But the black point not necessarely.

Indeed, the black point is rarely at neutral but is much closer than the white point of OB laden papers. Especially on printers with K inks.

However, Perceptual intent aligns with both the white point and black point while Rel Col only aligns with the white point (w/o BPC for those CMMs that offer it). So Rel Col will not align quite as well as Perceptual with device color. Still, both will be much closer without OBs.
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