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Old 12-31-2017, 07:20 PM   #1
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Lightbulb Night screen filter without affecting screenshots

Hello, and great thanks to you for considering to answer my LinuxQuestion:

I need a night screen filter for Linux, which does not cause the colour tone of screenshots and screencasts to be affected. Do you know such a useful tool?
Old 01-01-2018, 04:32 AM   #2
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what have you tried and did it work as desired or not?
you also might need to try different screenshot apps.
and web searches.
Old 01-01-2018, 05:28 AM   #3
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The night light might not affect screen shots. You should just try it.
Old 01-01-2018, 08:13 AM   #4
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With xrandr you can affect the brightness and gamma settings of X. Which should be independent of what a screen capture should see. There's a redshift thing that plays with those settings iirc. And various libxca type routes to do similar things.

$ xrandr --output eDP --brightness 0.5 --gamma 0.5:0.5:0.5

Where 1.0 is the assumed default values. And the --output is a valid screen for your system. Running xrandr without parms should list available and in use screens.

$ xrandr
Old 01-01-2018, 01:06 PM   #5
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Redshift-GUI works very well indeed.

Years ago, before moving to Linux, I used to use f.Lux in Windoze. Under Linux, f.Lux is command-line only.....and a wee bit complicated to get right.

RedshiftGUI does much the same thing for Linux.....and, in fact, I personally prefer the interface to that of f.Lux. You can get this from SourceForge:-

(I have to use something like this. Where I used to work, years ago, we were processing a very abrasive mineral, like sharp sand. It was a lot finer, though.....and air-flow helmets wouldn't entirely keep it out. It would get round the back of your eyeballs and cause scratching to the delicate tissue, leaving you with extremely sore eyes. Even now, years after leaving the place, my eyes are permanently sensitized to bright something like this for night-time use is, for me, a must-have item.)


There's a very small, lightweight command-line alternative, called SCT (Set Color Temperature). It's available from Github. You need to compile it yourself, but it really is a piece of cake to do so. If a blockhead like me can do it, then you know it's got to be easy..!

Download the tarball, and extract. Make sure your development tools are installed, or loaded; I'm afraid I've been using Puppy for so long I can't remember how this is done in the mainstream distros; in Pup we 'load' the 'devx' SFS package. Then 'unload' again when finished.

Open a terminal in the directory where you extracted it to, then enter into the terminal the command string found on line 23 of the 'Read Me' file:-

cc -std=c99 -O2 -I /usr/X11R6/include -o sct sct.c -L /usr/X11R6/lib -lm -lX11 -lXrandr
.....and within 10 seconds you'll get a compiled binary. Move this into /usr/bin, then you can run it using the following terminal command. Very simply

sct 3600
...for example. 3600 is a 'night-time' value (a warm, red-tinted hue).

sct 6500
...would give you a normal, daylight tint.

sct 8000
...would give you a very blue-white light. And so on.

I've used both of these for a while in Pup, and, so far, any screenshots I've taken at night with either of them don't seem to transfer the reddish hue to whatever I take a piccie of.

There's a short video I put together here, showing the process.....although no sound, I'm afraid. It was a demo I knocked up for another member of the Murga-Linux 'Puppy' Forums.

(It's almost certain to be different in whatever you happen to be running, although the principle remains the same.)

You might find the forum thread helpful, too:-


Last edited by Mike_Walsh; 01-01-2018 at 01:50 PM.


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