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Problem matching monitors

Problem matching monitors

2010-10-24 by Jim Miller

I thought I had a handle on using the Spyder 3 but tonight I hit a wall.
I have a desktop with two Dell 2408wfp monitors. I have them profiled at 6500 2.2 and 120cd.
I have a Dell notebook which I also profiled at 6500 2.2 120cd with the same Spyder in the same room.
First problem is that the Spyder tells me the room is 89cd when run from one computer and 120cd when run from the other. The location of the spyder itself never changed.
I went ahead and profiled all three displays and then using Lightroom displayed a white image.
The two desktop displays show the same color for white where the laptop shows a different one. The desktop compared to the laptop appears greenish, the laptop (not surprisingly) looks a bit magenta by comparison.
Questions:
Shouldn't the Spyder give a near identical reading of ambient regardless of which computer is driving it?
Shouldn't 128, 128, 128 produce the same apparent image on all three displays instead of obvious chromatic differences?
FWIW, the desktop displays have a gamut pretty close to AdobeRGB according to S3Elite software 4.02.
The laptop is limited to approximately sRGB according to S3E 4.02
Win7/64
thanks
jim

Re: [datacolor_group] Problem matching monitors

2010-10-24 by Laurie Solomon

I am sure that CD and David from Datacolor will give you an answer that is much more accurate and detailed than I; but I will attempt to put forth some proposed answers to your questions.
1) The ambient light reading will depend on a number of variables including the fact that over time the light source itself may change both in color temperature and in intensity as the duration of its being turned on increases and the source ages and/or warms up and/or external light sources that contribute to the ambient light within a room may change in intensity, direction, or type. Thus, the time between the measurements of the different computers may contribute to different readings. A est for this wqould be to take readings of the ambient light over an extended duration of a single computer and see if the readings change over time.
2) The meaning and effect of a given reading like 128 across different monitors for even the same identical image will depend on and vary with the chartacteristics and limitations of the individual monitors. Your two desktop monitors may have similar properties and characteristics as well as capabilities which may be very different from and greater or lesser than your laptop monitor. The same may be the case with respect to the impact of the video card on the monitors ability to render. You do not mention if the desktops are using separate or the same video card and if that card is the same as the one used by the laptop as well as the specifications of those video cards and the ages of the three monitors. These factors all come into play as variables. I think you really may have indirectly answered your own question when you not that the desktop monitor displays have an Adobe RGB 1998 gamut whereas the laptop has a sRGB gamut; this indicates that the color rendering capabilities of the two videocard/monitor combinations are not identical and do not have the same identical color space in which values are being interpreted.
At any rate, that is my two cents worth.

From: Jim Miller
Sent: Saturday, October 23, 2010 9:11 PM
Subject: [datacolor_group] Problem matching monitors

I thought I had a handle on using the Spyder 3 but tonight I hit a wall.
I have a desktop with two Dell 2408wfp monitors. I have them profiled at 6500 2.2 and 120cd.
I have a Dell notebook which I also profiled at 6500 2.2 120cd with the same Spyder in the same room.
First problem is that the Spyder tells me the room is 89cd when run from one computer and 120cd when run from the other. The location of the spyder itself never changed.
I went ahead and profiled all three displays and then using Lightroom displayed a white image.
The two desktop displays show the same color for white where the laptop shows a different one. The desktop compared to the laptop appears greenish, the laptop (not surprisingly) looks a bit magenta by comparison.
Questions:
Shouldn't the Spyder give a near identical reading of ambient regardless of which computer is driving it?
Shouldn't 128, 128, 128 produce the same apparent image on all three displays instead of obvious chromatic differences?
FWIW, the desktop displays have a gamut pretty close to AdobeRGB according to S3Elite software 4.02.
The laptop is limited to approximately sRGB according to S3E 4.02
Win7/64
thanks
jim

Re: [datacolor_group] Problem matching monitors

2010-10-24 by Cdtobie

>>Shouldn't the Spyder give a near identical reading of ambient regardless of which computer is driving it?

Where are you getting ambient light readings in Candelas?
 
>>Shouldn't 128, 128, 128 produce the same apparent image on all three displays instead of obvious chromatic differences?

Yes, it should, but these are different screen types, both in gamut, and in viewing angle. The gamut difference means your whites and grays are being constructed from more saturated RGBs with the desktop displays. The viewing angle means that the Spyder is reading colors that vary more with angle on the laptop. 

These factors add up to a difference to your eye. You could calibrate the laptop to a custom whitepoint in order to achieve a more acceptable visual match, if side-by-side use is the goal, but laptops are generally calibrated to native luminance (and maybe even native whitepoint) for use in uncontrolled environments. 
 
In my experience, Dell laptops are among the must challenging screens to calibrate; matching, say, Apple Cinema displays to a MacBook produces a much closer visual result. 

C. D. Tobie
Global Product Technology Mngr.
Digital Imaging & Home Theater
Datacolor.com
CDTobie@Datacolor.com
Show quoted textHide quoted text
On Oct 23, 2010, at 10:11 PM, Jim Miller <jim@...> wrote:

> Shouldn't the Spyder give a near identical reading of ambient regardless of which computer is driving it?
>  
> Shouldn't 128, 128, 128 produce the same apparent image on all three displays instead of obvious chromatic differences?
>  
> FWIW, the desktop displays have a gamut pretty close to AdobeRGB according to S3Elite software 4.02.
>  
> The laptop is limited to approximately sRGB according to S3E 4.02

Re: [datacolor_group] Problem matching monitors

2010-10-24 by C D Tobie

>>
I'm headed back down to the studio in a couple of hours to do some more investigation. S3E reports candelas when measuring ambient.

I assume that's actually Candelas per Meter Squared. Also, keep in mind that there are two apps involved: Elite, and the Utility, which runs when Elite is not running.  Since the Utility buffers it's measurements, so that a quick shadow over the Spyder won't cause a sudden warning about being out of range, the results won't necessarily be the same until the Utility has averaged a long series of readings and zeroed in on the average value...
 
C. David Tobie
Global Product Technology Manager
Digital Imaging and Home Theater
Datacolor inc. 
cdtobie@...
www.datacolor.com
Show quoted textHide quoted text
On Oct 24, 2010, at 10:27 AM, Jim Miller <jim@...> wrote:

> 
> I'm headed back down to the studio in a couple of hours to do some more investigation. S3E reports candelas when measuring ambient.

Re: [datacolor_group] Problem matching monitors

2010-10-24 by Jim Miller

Some followup:
I finally gave up trying to get the laptop to match the desktop. FWIW, the laptop has a very wide viewing angle throughout which no perceptible change in color occurs. This is a new Studio 1558 from Dell with an LED backlight. To add more confusion the applet that comes to adjust a variety of display settings shows the display as having a Gamma of 1.0. Moving the gamma setting to 1.8 or 2.2 in the applet emphasizes the midranges and washes out the display.
Attempting to profile the laptop either at gamma 1.0 or gamma 2.2 still shows the display with a gamut having very little more than sRGB. Not really practical for image editing.
After giving up on the laptop I went back to reprofiling the desktop displays at 160cd/m^2 but found them annoying bright. BTW, these displays must have carbon arc searchlights for backlights since only 25 or so out of 100 takes them to the 160cd/m^2 range. So I punted back to 6500/2.2/120 and profiled them both there.
I'm done.
jim

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