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Author Topic: Two calibrated screens - completely different colors  (Read 5539 times)

polasekr

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Two calibrated screens - completely different colors
« on: January 07, 2015, 10:42:33 pm »

Hi everybody,
I am new to color management. I purchased X-Rite I1 PRO 2 device and calibrated both my external wide gamut monitor DELL U2410 and build-in display on my laptop Fujitsu T902. I run Windows 7 and display is extended to laptop build-in display. Right there I can see huge difference in colors of wallpapers. I thought that it could be because the wallpapers are not color managed, so I tried to use photo in Photoshop program as a reference.  When I move the Photoshop window with the photo the way that it spawns across both screens, there is a obvious color difference - e.g. blue color on one screen turns into purple on the other. 
Is this something expected due to different display technologies? What should I do to correct it? I also appreciate any links to information regarding the color profiling monitors and printers, but for beginners.
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Simon Garrett

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Re: Two calibrated screens - completely different colors
« Reply #1 on: January 08, 2015, 03:55:20 am »

Hi everybody,
I am new to color management. I purchased X-Rite I1 PRO 2 device and calibrated both my external wide gamut monitor DELL U2410 and build-in display on my laptop Fujitsu T902. I run Windows 7 and display is extended to laptop build-in display. Right there I can see huge difference in colors of wallpapers. I thought that it could be because the wallpapers are not color managed,

Correct, the desktop isn't colour-managed.

...so I tried to use photo in Photoshop program as a reference.  When I move the Photoshop window with the photo the way that it spawns across both screens, there is a obvious color difference - e.g. blue color on one screen turns into purple on the other. 
Is this something expected due to different display technologies?

I'm not sure about Photoshop, but most software uses one profile for a window.  So if a window spans two monitors, the software uses one profile for both, and obviously one will be wrong.

What should I do to correct it? I also appreciate any links to information regarding the color profiling monitors and printers, but for beginners.

A better test, IMHO, is to open the same image in two instances of the same colour-managed program such as Windows Photo Viewer, one on each monitor, and each one wholly on one monitor, and compare the two.  When I do that, with different but calibrated/profiled monitors, they look the same on each monitor.

By the way: don't use web browsers to compare colour rendering.  Most are not fully colour-managed.  Only Firefox is fully colour-managed, with Safari a close second, but even those have issues.  Last time I checked, both look up only the profile for the main monitor, and used that on whichever monitor is used. 
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D Fosse

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Re: Two calibrated screens - completely different colors
« Reply #2 on: January 08, 2015, 04:07:03 am »

Also asked in the Adobe Color Management forum (with a reply from yours truly):

https://forums.adobe.com/thread/1674104

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When I move the Photoshop window with the photo the way that it spawns across both screens, there is a obvious color difference

This in itself is expected. Photoshop can only convert to one profile at a time. What happens when displaying in a color managed app like Photoshop, is a full profile conversion from document profile to display profile. These converted RGB values are sent to the display.

So Photoshop uses the profile for the display the image is on. When dragging the image over, PS uses that profile until it passes the half-way point over on the other, then it changes profile when you drop it.

That said, it's always a possibility that Windows isn't loading the correct profile for each display. This isn't a common problem, but it happens. You can check the default profile for each display under Control Panel > Color Management > Devices.
« Last Edit: January 08, 2015, 04:16:01 am by D Fosse »
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howardm

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Re: Two calibrated screens - completely different colors
« Reply #3 on: January 08, 2015, 07:29:34 am »

You'll be disappointed and confused to hear that 2 very different screens, calibrated to the same 'target' values will almost always appear 'different' to varying degrees.  In general, one picks and calibrates 1 screen to be the 'reference' and then tries to match the other one to it via modifying the white point during it's calbration.  It's tedious and takes a while to get it 'close' (keep notes!).  At some point, you'll end up saying 'it's good enough'.

Simon Garrett

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Re: Two calibrated screens - completely different colors
« Reply #4 on: January 08, 2015, 08:12:26 am »

You'll be disappointed and confused to hear that 2 very different screens, calibrated to the same 'target' values will almost always appear 'different' to varying degrees. 

True, but in my experience you can get pretty close.  Until recently I used two very different monitors: an HP LP2475w (wide gamut) and a much older Samsung (normal gamut).  Not only were the colour spaces very different, but the uncalibrated white point and gamma were different.  After calibration and profiling, when displaying the same image on both they looked very similar indeed.  Of course, the Samsung could not show colours outside its gamut, but for sRGB images, the two monitors were very close - both to the eye and measuring them with HCFR Colorimeter software. 

Perhaps I'm lucky, but it didn't take a lot of tedious adjustment - it just worked. 
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D Fosse

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Re: Two calibrated screens - completely different colors
« Reply #5 on: January 08, 2015, 08:44:02 am »

It is usually possible to get a pretty close match even with different brand/model displays, if (a) the two monitors in question are reasonably well-behaved (laptops usually don't qualify here), (b) the calibrator allows custom or native white (not just D65 or a Kelvin temperature), and (c) the monitor can be adjusted on the green-magenta axis in addition to blue-yellow.

The trick is to concentrate on the white point on the second unit (after the first is complete), using the OSD controls. When white points match as well as they can, go ahead and calibrate it normally to that white point.

However, just setting the same white point in the calibrator will usually result in a significant difference unless you're lucky.

To illustrate a not-so-well-behaved display, to put it mildly, here's how the LUT curve looked when I once tried to calibrate an hp laptop to D65. Note what happens near the white point (ouch...)
« Last Edit: January 08, 2015, 08:56:27 am by D Fosse »
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Simon Garrett

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Re: Two calibrated screens - completely different colors
« Reply #6 on: January 08, 2015, 09:14:13 am »

The trick is to concentrate on the white point on the second unit (after the first is complete), using the OSD controls. When white points match as well as they can, go ahead and calibrate it normally to that white point.

However, just setting the same white point in the calibrator will usually result in a significant difference unless you're lucky.

That matches my experience. 

Another difficulty can arise if you use different calibration/profiling software for the two monitors. You might say that would be a crazy thing to do, but here's why that happens with me.  My current setup is with an Eizo CS240 and an HP LP2475w.  I use an i1 Display Pro to calibrate/profile.  However, in order to program the hardware LUTs in the Eizo, I have to use Eizo's ColorNavigator software.  But that won't work with anything except Eizo monitors, so I have to use something else - currently x-rite's i1Profiler - to calibrate and profile the HP.  The two appear to interpret white point slightly differently. 
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digitaldog

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Re: Two calibrated screens - completely different colors
« Reply #7 on: January 08, 2015, 10:23:33 am »

The two appear to interpret white point slightly differently. 
To be expected. That's yet another reason one often needs vastly different settings for different displays to produce a visual match.
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D Fosse

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Re: Two calibrated screens - completely different colors
« Reply #8 on: January 08, 2015, 02:59:01 pm »

All of which goes to show that there is a visual aspect to calibration, it's not just a question of dialing in the numbers. The numbers that give you a visual match to paper white are the right numbers - whatever they happen to be. In fact setting the white point could and perhaps should be done entirely visually.

Often you can only adjust along the blue-yellow Kelvin scale, but not along the green-magenta axis. In that case it may be next to impossible to get it entirely right. This is again an advantage of a high-end integrated hardware calibrator like Colornavigator/Spectraview, where you can set white point freely in two dimensions.

When using a standard software calibrator like i1 Profiler, it may be best to set the white point using the monitor's OSD, and then calibrate to native white. Or even go one step further and set the calibrator to "profile only/no calibration". i1 Profiler doesn't allow this, but Argyll/dispcal does. This will only work with color managed apps of course, but with a good monitor it's a valid option.

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The two appear to interpret white point slightly differently

In your case you're using the same sensor, so that's one less variable. But there will always be slight differences between different combinations. On the Eizo CG246 I can see a very slight difference between using the i1 D3 and the built-in sensor. They're equally "accurate"; they just require slightly different white point settings.
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polasekr

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Re: Two calibrated screens - completely different colors
« Reply #9 on: January 08, 2015, 10:22:27 pm »

Thank you  everybody for your vary valuable input.

I tested the case when you drop the photoshop window on the other screen, the image adjusts correctly. That is good.
I also tried to do the test with two windows of Windows photo viewer, but I wasn't successful there. I have a problem that image with embedded color profile is significantly darker and colors don't match with same image in photoshop on a same screen. I checked setting of color management in control panel, but no luck. I need more time to play with it, to figure out why I am having this problem.

I post update as soon as I get to the bottom of this problem.

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