[argyllcms] Re: "Wrong" ambient light reading with colormunki

It's a bummer, because I just ordered CM today hoping to get better monitor
profile than with dtp94. I wish I knew it before I bought it.

On Mon, May 10, 2010 at 9:33 PM, Roger Breton <graxx@xxxxxxxxxxxx> wrote:

> Hi Marco,
>
> Don't trust a reading of 0.09 cd/m2 with any instruments except from very
> expensive colorimeters and spectroradiometers. Very few instruments have
> the
> needed sensitivity to measure that few photons. You could aim for 0.5 to
> 1.0.
>
> Best / Roger
>
> > -----Original Message-----
> > From: argyllcms-bounce@xxxxxxxxxxxxx [mailto:argyllcms-
> > bounce@xxxxxxxxxxxxx] On Behalf Of Marco Presi
> > Sent: 10 mai 2010 21:01
> > To: argyllcms@xxxxxxxxxxxxx
> > Subject: [argyllcms] "Wrong" ambient light reading with colormunki
> >
> > Hi,
> >
> > I am trying to calibrate an LCD display by using a colormunki.  As I am
> doing
> > these things for the first time, I am trying to compare results with the
> x-rite
> > software coming with the device and argyll.
> >
> > I found that the ambient light measurement is constantly "lower" if made
> > with argyll. I have been very careful in keeping the same conditions
> while
> > during the measurements: as an example, when the x-rite software returns
> > 80 lux, argyll returns approx. 50 lux. Doing the same measurement on a
> > debian gnu/linux box gives exactly the same result (please note that the
> x-
> > rite software is not available on linux). I tried the same measurements
> at
> > different night times and at different days: the values I obtain can be
> > reproduced with good accuracy (x-rite software returns 80, argyll approx.
> > 50).
> >
> > how could this be fixed? could this problem affect all the calibration
> process?
> > (I mean, if the sensor reads with an offset, this error is made also
> during the
> > patch examinations?)
> >
> > In addition, when completing the calibration with argyll (I tried to read
> the
> > docs carefully), the black point looks too bright: I tried to compensate
> it by
> > using all the options I found (-B, -f,), but nothing changes. I am
> attaching here
> > the output of dispcal: at the beginning, it declares that the target
> black
> level
> > is the "native", but it then set the target black to 0.9. However, as can
> be
> > seen from the "dispcal -yl -R"
> > output, the monitor is able to reach black levels as low as 0.09 cd/m^2
> >
> > So, why during calibration dispcal decides to shift up the black point
> which
> > results in a lower contrast?!? This behavior is also identical both in
> windows
> > and linux.
> >
> >
> > Thanks for your attention!
> >
> >
> > Ciao,
> >
> > Marco
> >
> >
> > zsh 1009 % dispcal -yl -R
> > Set instrument sensor to calibration position,  and then hit any key to
> > continue,  or hit Esc or Q to abort:
> > Calibration complete
> >
> > Place instrument on test window.
> > Hit Esc or Q to give up, any other key to continue:
> > Uncalibrated response:
> > Black level = 0.09 cd/m^2
> > White level = 91.39 cd/m^2
> > Aprox. gamma = 2.17
> > Contrast ratio = 975:1
> > White chromaticity coordinates 0.3283, 0.3400
> > White    Correlated Color Temperature = 5688K, DE 2K to locus =  2.1
> > White Correlated Daylight Temperature = 5689K, DE 2K to locus =  2.9
> > White        Visual Color Temperature = 5634K, DE 2K to locus =  2.0
> > White     Visual Daylight Temperature = 5763K, DE 2K to locus =  2.7
> > Effective LUT entry depth seems to be 8 bits The instrument can be
> removed
> > from the screen.
> >
> >
> >
> > ---------
> > zsh 1008 % dispcal -yl -b90 -gs -t5500 -a40 -f -v5 sm206bw Setting up the
> > instrument
> > Instrument Type:   ColorMunki
> > Serial Number:     2021361
> > Firmware version:  288
> > Chip ID:           01-60d06812000029
> > Version string:    'colormunki FW V1.32  Build Nr. 1303'
> > Calibration Ver.:  6
> > Production No.:    35276
> > Set instrument sensor to calibration position,  and then hit any key to
> > continue,  or hit Esc or Q to abort:
> > Calibration complete
> >
> > Place instrument on test window.
> > Hit Esc or Q to give up, any other key to continue:
> > Display type is LCD
> > Target white = 5500.000000 degrees kelvin Daylight spectrum Target white
> > brightness = 90.000000 cd/m^2 Target black brightness = native brightness
> > Target gamma = sRGB curve
> >
> > Display adjustment menu:
> > Press 1 .. 7
> > 1) Black level (CRT: Offset/Brightness)
> > 2) White point (Color temperature, R,G,B, Gain/Contrast)
> > 3) White level (CRT: Gain/Contrast, LCD: Brightness/Backlight)
> > 4) Black point (R,G,B, Offset/Brightness)
> > 5) Check all
> > 6) Measure and set ambient for viewing condition adjustment
> > 7) Continue on to calibration
> > 8) Exit
> > Doing check measurements
> > Black = XYZ   0.05   0.05   0.06
> > Grey  = XYZ  19.96  20.14  26.49
> > White = XYZ  87.09  90.23  88.64
> > 1%    = XYZ   0.77   0.79   1.05
> >
> >   Target Brightness = 90.00, Current = 90.23, error =  0.3%
> >   Target 50% Level  = 19.63, Current = 20.14, error =  0.6%
> >   Target Near Black =  0.90, Current =  1.07, error =  0.2%
> >   Target white = x 0.3325, y 0.3475, Current = x 0.3275, y 0.3393, error
> =
> >  4.38 DE
> >   Target black = x 0.3325, y 0.3475, Current = x 0.2969, y 0.3013, error
> =
> > 16.88 DE
> >
> > Press 1 .. 7
> > 1) Black level (CRT: Offset/Brightness)
> > 2) White point (Color temperature, R,G,B, Gain/Contrast)
> > 3) White level (CRT: Gain/Contrast, LCD: Brightness/Backlight)
> > 4) Black point (R,G,B, Offset/Brightness)
> > 5) Check all
> > 6) Measure and set ambient for viewing condition adjustment
> > 7) Continue on to calibration
> > 8) Exit
> > Exiting
> > The instrument can be removed from the screen.
> >
> >
> >
> >
>
>
>
>
>


-- 
AAK

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