How to Programmatically Invert Screen Colors in Linux

How to programmatically invert screen colors in Linux

You could use xcalib to do what you want.

For example, a simple bash script to invert the screen colors would look like this:

#!/bin/bash
xcalib -invert -alter

How can I generate the opposite color according to current color?

UPDATE: Production-ready code on GitHub.

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This is how I'd do it:

1. Convert HEX to RGB
2. Invert the R,G and B components
3. Convert each component back to HEX
4. Pad each component with zeros and output.

function invertColor(hex) {
    if (hex.indexOf('#') === 0) {
        hex = hex.slice(1);
    }
    // convert 3-digit hex to 6-digits.
    if (hex.length === 3) {
        hex = hex[0] + hex[0] + hex[1] + hex[1] + hex[2] + hex[2];
    }
    if (hex.length !== 6) {
        throw new Error('Invalid HEX color.');
    }
    // invert color components
    var r = (255 - parseInt(hex.slice(0, 2), 16)).toString(16),
        g = (255 - parseInt(hex.slice(2, 4), 16)).toString(16),
        b = (255 - parseInt(hex.slice(4, 6), 16)).toString(16);
    // pad each with zeros and return
    return '#' + padZero(r) + padZero(g) + padZero(b);
}

function padZero(str, len) {
    len = len || 2;
    var zeros = new Array(len).join('0');
    return (zeros + str).slice(-len);
}

Example Output:

Advanced Version:

This has a bw option that will decide whether to invert to black or white; so you'll get more contrast which is generally better for the human eye.

function invertColor(hex, bw) {
    if (hex.indexOf('#') === 0) {
        hex = hex.slice(1);
    }
    // convert 3-digit hex to 6-digits.
    if (hex.length === 3) {
        hex = hex[0] + hex[0] + hex[1] + hex[1] + hex[2] + hex[2];
    }
    if (hex.length !== 6) {
        throw new Error('Invalid HEX color.');
    }
    var r = parseInt(hex.slice(0, 2), 16),
        g = parseInt(hex.slice(2, 4), 16),
        b = parseInt(hex.slice(4, 6), 16);
    if (bw) {
        // https://stackoverflow.com/a/3943023/112731
        return (r * 0.299 + g * 0.587 + b * 0.114) > 186
            ? '#000000'
            : '#FFFFFF';
    }
    // invert color components
    r = (255 - r).toString(16);
    g = (255 - g).toString(16);
    b = (255 - b).toString(16);
    // pad each with zeros and return
    return "#" + padZero(r) + padZero(g) + padZero(b);
}

Example Output:

Using colors with printf

You're mixing the parts together instead of separating them cleanly.

printf '\e[1;34m%-6s\e[m' "This is text"

Basically, put the fixed stuff in the format and the variable stuff in the parameters.

Switch application fullscreen mode programmatically on Linux Mate / Ubuntu

A friend gave me the tip to check out the wmctrl program. The sources of this program led me to the XLib or XCB library and setting the window to _NET_WM_STATE_FULLSCREEN.

I guess this could be done in .NET by P/Invoking the native lib. Then again it seems much easier to write a shell script that determines the windows ID and calls the wmctrl utility and call that script from the .net application.

Determine font color based on background color

I encountered similar problem. I had to find a good method of selecting contrastive font color to display text labels on colorscales/heatmaps. It had to be universal method and generated color had to be "good looking", which means that simple generating complementary color was not good solution - sometimes it generated strange, very intensive colors that were hard to watch and read.

After long hours of testing and trying to solve this problem, I found out that the best solution is to select white font for "dark" colors, and black font for "bright" colors.

Here's an example of function I am using in C#:

Color ContrastColor(Color color)
{
    int d = 0;
    
    // Counting the perceptive luminance - human eye favors green color...      
    double luminance = (0.299 * color.R + 0.587 * color.G + 0.114 * color.B)/255;
    
    if (luminance > 0.5)
       d = 0; // bright colors - black font
    else
       d = 255; // dark colors - white font
                
    return  Color.FromArgb(d, d, d);
}

This was tested for many various colorscales (rainbow, grayscale, heat, ice, and many others) and is the only "universal" method I found out.

Edit

Changed the formula of counting a to "perceptive luminance" - it really looks better! Already implemented it in my software, looks great.

Edit 2
@WebSeed provided a great working example of this algorithm: http://codepen.io/WebSeed/full/pvgqEq/

Dark color scheme for Eclipse

As posted to a few related questions already, I'm working on a plugin for easy, cross-editor color theme management:

http://marketplace.eclipse.org/content/eclipse-color-theme

It is still work in progress, but already supports many editors and a few dark color themes.

stdlib and colored output in C

All modern terminal emulators use ANSI escape codes to show colours and other things.

Don't bother with libraries, the code is really simple.

More info is here.

Example in C:

#include <stdio.h>

#define ANSI_COLOR_RED     "\x1b[31m"
#define ANSI_COLOR_GREEN   "\x1b[32m"
#define ANSI_COLOR_YELLOW  "\x1b[33m"
#define ANSI_COLOR_BLUE    "\x1b[34m"
#define ANSI_COLOR_MAGENTA "\x1b[35m"
#define ANSI_COLOR_CYAN    "\x1b[36m"
#define ANSI_COLOR_RESET   "\x1b[0m"

int main (int argc, char const *argv[]) {

  printf(ANSI_COLOR_RED     "This text is RED!"     ANSI_COLOR_RESET "\n");
  printf(ANSI_COLOR_GREEN   "This text is GREEN!"   ANSI_COLOR_RESET "\n");
  printf(ANSI_COLOR_YELLOW  "This text is YELLOW!"  ANSI_COLOR_RESET "\n");
  printf(ANSI_COLOR_BLUE    "This text is BLUE!"    ANSI_COLOR_RESET "\n");
  printf(ANSI_COLOR_MAGENTA "This text is MAGENTA!" ANSI_COLOR_RESET "\n");
  printf(ANSI_COLOR_CYAN    "This text is CYAN!"    ANSI_COLOR_RESET "\n");

  return 0;
}

How to color System.out.println output?

No, but there are third party API's that can handle it

http://www.javaworld.com/javaworld/javaqa/2002-12/02-qa-1220-console.html

Edit: of course there are newer articles than that one I posted, the information is still viable though.

Above link is dead, see this question instead: How to print color in console using System.out.println?

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