ColorHug red shift workaround

As most of you probably know already, there is a cool (and affordable) little colorimeter available now called the ColorHug, and it’s open-source too (including all companion software).

As the ColorHug’s firmware is still being improved, some people have noticed a profile created with the ColorHug makes their display shift excessively to the red, possibly due to a slight measurement inaccuracy.

A display profile generally consist of two main parts, first there is the vcgt (sometimes also called VideoLUT), which is loaded and applied by X11 itself. This is usually a correction for a displays white point (which is where it goes wrong). And the second part is gamma+matrix (which is gamma/hue/saturation correction). So to avoid the red shift we have to skip the first part of profile creation.

To prepare I recommend you (try to) do the following (for this particular procedure):

  1. Note down your display old settings (if you care to go back to these).
  2. Reset your display’s settings to factory defaults.
  3. Adjust the display’s brightness to a comfortable level (you really often don’t need maximum brightness).
  4. Generally it’s a good idea to leave contrast at the manufacturers default.
  5. Change the displays color temperature to 6500K if possible (You might notice your display shift a bit to the yellow).

Then execute the following commands in a Terminal

# targen -v -d 3 -G -f 64 make_model
# ENABLE_COLORHUG=1 dispread -v -y l make_model
# colprof -v -A "Make" -M "Model" -D "Make Model" \
          -C "Copyright (c) 2012 John Doe. Some rights reserved." \
          -q l -a G make_model

The above commands skip vcgt creation with dispcal and do a fairly simple set of measurements and create a fairly simple ICC profile. This simplicity gets us increased robustness in the profile’s creation at the expense of potential accuracy. To be honest I wouldn’t be surprised if commercial vendors use a similar strategy in their entry-level colorimetry products for the consumer market.

You’ll need to either manually import the resulting profile into GNOME Color Manager (to setup the profile at login), or directly configure it in programs like the GIMP. You can load an image like this in GIMP to check if the resulting profile makes sense. Please do mind GIMP has color management disabled by default, so you need to set it up in the Preferences.

Even with the above method, the resulting profile may still be a bit off in the reds (though it will only be visible in color managed applications). If this is still an issue for you, you could try the Community Average CCMX, or possibly my Dell U2212HM CCMX, for which I’ve gotten decent results on non-Dell displays too.

Posted by on June 15, 2012 in color