Background: More red / Less blue at night

To save the eyes at night, adding more red and/or subtracting blue, is becoming popular in Windows 10 (blue-light filter) and Linux; Gnome Desktop (Night Light) and Ubuntu Unity Desktop with add-ons such as Red Shift or f.lux.

I'm wondering how to accomplish the same with Ubuntu's built-in command line xrandr <monitor> --gamma 1:1:1 feature. The 1:1:1 represents percentage of red:green:blue. I presume 1 = 100%. I'm not sure if the above packages add more red (1.2:1:1) for ~20% increase or reduce blue (1:1:0.8) for ~20% decrease or both for ~40% change.

Gnome Night Light example doesn't help

According to OMG Ubuntu, within Gnome's Night Light you can use these numerical values:

• 1000 — Lowest value (super warm/red)
• 4000 — Default night light on temperature
• 5500 — Balanced night light temperature
• 6500 — Default night light off temperature
• 10000 — Highest value (super cool/blue)

To test these numerical values, how would does one translate them to override the default --gamma 1:1:1?

What xorg's documentation says

Xorg's documentation doesn't say very much about --gamma controls:

−−gamma red:green:blue

• Set the specified floating point values as gamma correction on the crtc currently attached to this output. Note that you cannot get two different values for cloned outputs (i.e.: which share the same crtc) and that switching an output to another crtc doesn’t change the crtc gamma corrections at all.

Floating decimal points will be helpful because the script I want to upgrade sets xbacklight brightness slowly once a minute over a 90 to 120 minute transition period at dawn and dusk. I want to enhance the script with both xrandr --brightness software support for external monitors and OLED built in displays and xrandr --gamma support for red light / blue light filters. Xorg doesn't say how many decimal positions are supported but I think I think I will set bc calculations should be to 3 or 4 decimal positions for readability / precision balance.

Summary

I'm hoping to mimic what "the big guys" at Microsoft and Gnome are doing with their "more red" and/or "less blue" techniques. I haven't delved into Wayland yet but answers using that system will also be appreciated as it will no doubt be a future concern.

What adjustment to --gamma 1:1:1 are appropriate for night time?

I have a DELL U2410 monitor connected to a Compaq 100B desktop equipped with an integrated AMD/ATI graphics card (AMD E-350). The installed O/S is Ubuntu 10.04 LTS.

The computer is connected to the monitor via the DVI connection.

The problem is that I cannot set the desktop resolution to the native 1920x1200. The maximum allowed resolution is 1600x1200.

Doing some research I found about the xrandr utility. Unfortunately, when trying to use it I cannot configure it to the required resolution. First, it does not report the output name (which supposed to be DVI-0), saying default instead. Without it I cannot use the --fb option.

The EDID utility seems to identify the monitor well. Here's the output from get-edid:

    # EDID version 1 revision 3
Section "Monitor"
    # Block type: 2:0 3:ff
    # Block type: 2:0 3:fc
    Identifier "DELL U2410"
    VendorName "DEL"
    ModelName "DELL U2410"
    # Block type: 2:0 3:ff
    # Block type: 2:0 3:fc
    # Block type: 2:0 3:fd
    HorizSync 30-81
    VertRefresh 56-76
    # Max dot clock (video bandwidth) 170 MHz
    # DPMS capabilities: Active off:yes  Suspend:yes  Standby:yes

    Mode    "1920x1200" # vfreq 59.950Hz, hfreq 74.038kHz
        DotClock    154.000000
        HTimings    1920 1968 2000 2080
        VTimings    1200 1203 1209 1235
        Flags   "-HSync" "+VSync"
    EndMode
    # Block type: 2:0 3:ff
    # Block type: 2:0 3:fc
    # Block type: 2:0 3:fd
EndSection

but the xrandr -q command returns:

Screen 0: minimum 640 x 400, current 1600 x 1200, maximum 1600 x 1200
default connected 1600x1200+0+0 0mm x 0mm
   1600x1200       0.0* 
   1280x1024       0.0  
   1152x864        0.0  
   1024x768        0.0  
   800x600         0.0  
   640x480         0.0  
   720x400         0.0  

When I try to set the resolution, I get:

$ xrandr --fb 1920x1200
xrandr: screen cannot be larger than 1600x1200 (desired size 1920x1200)

$ xrandr --output DVI-0 --auto
warning: output DVI-0 not found; ignoring

How can I set the screen resolution to 1920x1200? Why doesn't xrandr identify the DVI-0 output?

Note that the same computer running Ubuntu version higher than 10.04 detects the correct resolution with no problems. On this machine I cannot upgrade due to some legacy hardware compatibility problems.

Also, I don't see any optional screen drivers available in the Hardware Drivers dialog.

----

UPDATE:

following the answer to this question, I got some advance. Now the required mode is listed in the xrandr -q list, but I can't switch to that mode. Using the Monitors applet (which now shows the new mode), I get the response that:

The selected configuration for displays could not be applied. Could not set the configuration to CRTC 262.

From the command line it looks like this:

$ cvt 1920 1200 60
# 1920x1200 59.88 Hz (CVT 2.30MA) hsync: 74.56 kHz; pclk: 193.25 MHz
Modeline "1920x1200_60.00"  193.25  1920 2056 2256 2592  1200 1203 1209 1245 -hsync +vsync

$ xrandr --newmode "1920x1200_60.00"  193.25  1920 2056 2256 2592  1200 1203 1209 1245 -hsync +vsync

$ xrandr -q
Screen 0: minimum 640 x 400, current 1600 x 1200, maximum 1600 x 1200
default connected 1600x1200+0+0 0mm x 0mm
   1600x1200       0.0* 
   1280x1024       0.0  
   1152x864        0.0  
   1024x768        0.0  
   800x600         0.0  
   640x480         0.0  
   720x400         0.0  
  1920x1200_60.00 (0x120)  193.0MHz
        h: width  1920 start 2056 end 2256 total 2592 skew    0 clock   74.5KHz
        v: height 1200 start 1203 end 1209 total 1245           clock   59.8Hz

$ xrandr --addmode default 1920x1200_60.00

$ xrandr -q
Screen 0: minimum 640 x 400, current 1600 x 1200, maximum 1600 x 1200
default connected 1600x1200+0+0 0mm x 0mm
   1600x1200       0.0* 
   1280x1024       0.0  
   1152x864        0.0  
   1024x768        0.0  
   800x600         0.0  
   640x480         0.0  
   720x400         0.0  
   1920x1200_60.00   59.8  

$ xrandr --output default --mode 1920x1200_60.00
xrandr: Configure crtc 0 failed

Another piece of info (if it helps anyone):

$ sudo lshw -c video
  *-display UNCLAIMED     
       description: VGA compatible controller
       product: ATI Technologies Inc
       vendor: ATI Technologies Inc
       physical id: 1
       bus info: pci@0000:00:01.0
       version: 00
       width: 32 bits
       clock: 33MHz
       capabilities: pm pciexpress msi bus_master cap_list
       configuration: latency=0
       resources: memory:c0000000-cfffffff(prefetchable) ioport:f000(size=256) memory:feb00000-feb3ffff

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UPDATE 2: Here's the updated lshw listing:

$ sudo lshw -numeric -c video
  *-display UNCLAIMED     
       description: VGA compatible controller
       product: ATI Technologies Inc [1002:9802]
       vendor: ATI Technologies Inc [1002]
       physical id: 1
       bus info: pci@0000:00:01.0
       version: 00
       width: 32 bits
       clock: 33MHz
       capabilities: pm pciexpress msi bus_master cap_list
       configuration: latency=0
       resources: memory:c0000000-cfffffff(prefetchable) ioport:f000(size=256) memory:feb00000-feb3ffff

If I have only the internal monitor (LVDS1) with an xrandr -o left command. Now I want to attach a second monitor, say to HDMI1. Then I'd like to rotate only the internal monitor, but not the external one. I tried the following (with no external attached though, since I am mobile currently), but that does not do anything:

xrandr --output LVDS1 -o left

How can I rotate only one monitor?

I do need some command line, since I want to put this into a script.

I've been trying to set up an external monitor for a bit, finally got it mostly working except the resolution is off. My monitor's native res is 1600x900, which I finally got to show up in xrandr:

user:~$ xrandr
xrandr: Failed to get size of gamma for output default
Screen 0: minimum 640 x 480, current 1024 x 768, maximum 1600 x 900
default connected 1024x768+0+0 0mm x 0mm
   1024x768        0.0* 
   800x600         0.0  
   640x480         0.0  
   1600x900       59.9

However when I try to change the resolution I get the following error:

user:~$ xrandr --output default --mode 1600x900
xrandr: Failed to get size of gamma for output default
xrandr: Configure crtc 0 failed

After installing Ubuntu 10.04 with my Samsung SyncMaster B2030, native resolution (1600X900) is not found in the list of resolutions.