Some time ago I bought a Lenovo Pro2840m (microcode version LN3.01), which mostly works fine with OS X including 4k SST 60Hz HiDPI, but I have had one problem with it.
When using a Displayport connection but not with HDMI, the blacks and whites are both crushed as if the display was expecting a 16-235 luminance range but receiving the normal 0-255.
I first tried using patch-edid.rb to force RGB mode, but this only resulted in the "Television: Yes" line disappearing from the System Information list with no observable change to the display. In any case, this fix would appear to deal with the opposite of my problem.
To work around this problem, I wanted to create an ICC color profile that restricts the RGB luminance to the 16-235 range. Unfortunately, GUI programs that deal with color profiles are sorely lacking when it comes to overriding the curves that they automatically create based on colorimeter measurements.
Instead I used iccxml (along with the sampleicc library) to combine the default sRGB color space information with a 16-235 "vcgt" video card LUT. I have attached this file.
This file works well with the Lenovo Pro2840m set to either the sRGB color preset (which unfortunately locks the brightness setting at a too-high value for me) or a custom color setting of around 70/70/70. Note the the monitor clips highlights if the custom values are set higher than 77/77/77. The contrast setting does not affect the monitor's gamma curve, but should just be set to 100 (default 80).
When using a Displayport connection but not with HDMI, the blacks and whites are both crushed as if the display was expecting a 16-235 luminance range but receiving the normal 0-255.
I first tried using patch-edid.rb to force RGB mode, but this only resulted in the "Television: Yes" line disappearing from the System Information list with no observable change to the display. In any case, this fix would appear to deal with the opposite of my problem.
To work around this problem, I wanted to create an ICC color profile that restricts the RGB luminance to the 16-235 range. Unfortunately, GUI programs that deal with color profiles are sorely lacking when it comes to overriding the curves that they automatically create based on colorimeter measurements.
Instead I used iccxml (along with the sampleicc library) to combine the default sRGB color space information with a 16-235 "vcgt" video card LUT. I have attached this file.
This file works well with the Lenovo Pro2840m set to either the sRGB color preset (which unfortunately locks the brightness setting at a too-high value for me) or a custom color setting of around 70/70/70. Note the the monitor clips highlights if the custom values are set higher than 77/77/77. The contrast setting does not affect the monitor's gamma curve, but should just be set to 100 (default 80).