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Saturday, April 27, 2013

••◊ Color calibrating a video field monitor

I was recently inspired by a post over at NegativeSpaces.com by Ben Cain. He wrote about calibrating a high end Sony OLED production monitor via a X-Rite i1 Display Pro and custom Sony software.  That got me thinking about my own predicament with my Marshall field monitor.  It's been OK for the most part, but I never felt like I could trust it for color accuracy.  It's always seem warmer to me than my two calibrated PC monitors, one of them being an HP DreamColor.

What I had laying around is an X-Rite i1 Display 2.  It's not quite the same as the newer "Pro" model, but I had free access to it.  The problem is that the Sony software doesn't support the non-Pro model, so that was a dead end.  The X-Rite iProfile software wanted the Pro model as well.  After a quick google search I found HCFR Colorimeter.

HFRC is free software, and it definitely has it's quirks, but it does exactly what I need it to do for the moment, that is correct the white point of my field monitor to D65.  Since I didn't have an DVI to HDMI converter I simply took a very, very over-exposed picture on my Canon DSLR and drove the monitor with the 100% white picture as a white reference input.  When I get the converter I'll also be able to measure saturation and RGB bias - maybe later.

Like I mentioned, the software has it's quirks.  One big one is that you have to replace the standard X-Rite i1 driver with the custom driver that comes in the HFRC installation directory.  Without that change the software won't talk to the colorimeter.  After that difficulty, I was up and running.

When you click the "Go" button on the software the screen changes to a sequence of R-G-B, gray, and white.  Since there's no real synchronization between the colorimeter and the software I just had the DSLR display the white picture during the calibration process.  This would ideally give me a D65 white reference.

Well...it didn't.  If you click on the picture to enlarge it you'll see that the "D65" setting on the Marshall is very close to standard illuminant B (4874K).  So it made perfect sense why the field monitor always appeared warmer than it should be.  I was dealing with setting sun warm daylight instead of noon daylight.  For those nerdy enough to understand, the (x,y) coordinates were (x,y)=(0.346, 0.367).  For those not nerdy enough to understand you can visually see that the pink dot is pushed away from D65 toward orange.

After mainly adjusting the green gain on the Marshall monitor (be sure to set the "Color Temperature" to "User" first), the color temperature agreed with D65 quite nicely.  D65 has CIE coordinates of (x,y)=(0.313, 0.329) and the colorimeter measurement showed (x,y)=(0.313, 0.330).  Probably as close as I'm going to to get.  All it took was a little tweaking. 

Next time I go by the electronic store I'm going to pick up a DVI to HDMI converter and see if I can complete the calibration by adjusting the RGB bias and the saturation controls.  It makes a huge difference when you know you can trust your tools for good results.  Hopefully I'll be able to further trust my monitor in the near future.

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