From Rgb to Cmyk

Question

Given 3 bytes or RGB as input, calculate the nearest CMYK values, and output them.

• create either a function with parameters and return value or a program that operates on stdin/stdout
• use the color profile of your choice, but provide a reference
• input may be either separate numeric values in range [0;255] or a 6 digit hex string
• output should be separate numeric values ranging either [0;1] or [0;100]
• standard code golf: no loopholes, shortest code wins
• extravagant ideas are welcome

sample data:

input             output
108,174,106       [0.3793103448275862, 0.0, 0.3908045977011494, 0.3176470588235294]
0,0,0             0,0,0,1
170,255,238       33,0,7,0  
0x0088ff          1,0.4667,0,0
[250,235,215]     [0,6,14,1.96]  
#123456           .7907,.3953,0,.6627

• Uncalibrated mapping is fine and probably the easiest
• No input validation required; floats are allowed (ranging from 0 to 255), but may also be rounded
• Output format should be either clearly commented or obvious; i.e.:
  1. CMYK in that order
  2. does not matter if percentage [0;100] or pure numbers [0;1]
• Testing should include the trivial example [0,0,0].

This site has the most digits of online tools that I could find. Does anyone know a tool that gives more than 4 digits?

Answer 1

Dyalog APL, 16 15 bytes

1-⊢(÷,255÷⍨⊢)⌈/

1 minus 1-
 X divided by ÷ Y, followed by , 255 dividing 255÷⍨ Y ⊢, where
  X is itself ⊢ (i.e. the list of RGB values), and
  Y is the max /⌈ (of the RGB values).

$$ \begin{cases} J = max(R,G,B)\\ C = 1-\frac{R}{J}\\ M = 1-\frac{G}{J}\\ Y = 1-\frac{B}{J}\\ K = 1-\frac{J}{255}\\ \end{cases} $$

TryAPL!

Credits:
 ∘ -1 byte by ngn.

Answer 2

C#, 88 86 85 84 bytes

(r,g,b)=>{float[]a={r,g,b,1};var j=a.Max();a[3]=j*j/255;return a.Select(x=>1-x/j);};

output for 108,174,106:

0.3793104
0
0.3908046
0.3176471

Since OP allows function I submitted only the lambda. You can find a running demo on .NetFiddle. I am not a golfer, I post for fun. Also, it is my first answer \o/. Feel free to comment any improvement :)

Kudos to Leaky Nun for the formula.

caveat: it doesn´t work for [0,0,0] (thank you Titus)

Answer 3

Python, 46 bytes

lambda*c:[1-i/max(c)for i in c]+[1-max(c)/255]

Requires input to be floats in Python 2, fairly sure it doesn't in 3.

Answer 4

JavaScript (ES6), 58 51 bytes

a=>[...a.map(e=>1-e/m||1,m=Math.max(...a)),1-m/255]

Accepts an array [R, G, B] (add 7 bytes for separate parameters) and returns an array [C, M, Y, K] using the uncalibrated colour mapping.

Answer 5

Mathematica, 36 28 33 bytes

List@@ColorConvert[{##}/255,"CMYK"]&

After liberalization of I/O formats, golfed further: List@@#~ColorConvert~"CMYK"&

Anonymous function, that does what is asked.

The old function takes three arguments from 0 to 255 (anything beyond this range will be automatically clipped to this range) and returns an array of "CMYK" values between 0. and 1.

Example (for old function):

List @@ ColorConvert[{##}/255, "CMYK"] &[108, 174, 106]

{0.37931, 0., 0.390805, 0.320313}

Since arrays are allowed as input, 33 bytes:

List@@ColorConvert[#/255,"CMYK"]&

Of course the built-in function handles {0, 0, 0} properly and returns {0, 0, 0, 1}.

Answer 6

SmileBASIC, 73 72 bytes

INPUT R,G,B
J=MAX(R,G,B)IF!J THEN?0,0,0,1 ELSE?1-R/J,1-G/J,1-B/J,1-J/255

Could be much shorter.

Answer 7

Lithp, 114 bytes

#R,G,B::((var J(max R G B))(if(!= 0 J)((list(- 1(/ R J))(- 1(/ G J))(- 1(/ B J))(- 1(/ J 255))))((list 0 0 0 1))))

Try it online!

• Saved 6 bytes (forgot that max takes any number of arguments)

I'm not quite sure this is right. The first two results with the sample data are correct, but the rest are not (see the Try it online.)

Uses the implementation described nicely as follows:

$$ \begin{cases} J = max(R,G,B)\\ C = 1-\frac{R}{J}\\ M = 1-\frac{G}{J}\\ Y = 1-\frac{B}{J}\\ K = 1-\frac{J}{255}\\ \end{cases} $$

Answer 8

Pyth, 24 21 18 24 21 bytes

Life is a round trip, indeed.

=cR255Q+mc--1dK-1JeSQJQK
=cR255Q+mc-JeSQdJQ-1J
+mc-JeSQdJQ-1cJ255
+mc-JeSQd+J^T_15Q-1cJ255
+m-1?JeSQcdJ1Q-1cJ255

Test suite.

Sample input: 108,174,106

Sample output: [0.3793103448275862, 0.0, 0.3908045977011494, 0.3176470588235294]

Sample input: 0,0,0

Sample output: [0, 0, 0, 1.0]

Formula used:

$$ \begin{cases} J = max(R,G,B)\\ C = 1-\frac{R}{J}\\ M = 1-\frac{G}{J}\\ Y = 1-\frac{B}{J}\\ K = 1-\frac{J}{255}\\ \end{cases} $$

Old formula: http://i.stack.imgur.com/ZtPD6.gif

Old formula: http://i.stack.imgur.com/Nqi9F.gif

Answer 9

Bash + ImageMagick, 69 bytes

convert "xc:$1[1x1]" -colorspace cmyk txt:-|grep -o '([^)]*)'|head -1

Example:

$ ./rgb2cmyk.sh "#6CAE6A"
(38%,0%,39%,32%)

$ ./rgb2cmyk.sh "#000000"
(0%,0%,0%,100%)

$ ./rgb2cmyk.sh "#AAFFEE"
(33%,0%,7%,0%)

$ ./rgb2cmyk.sh "#0088ff"
(100%,47%,0%,0%)

$ ./rgb2cmyk.sh "#FAEBD7"
(0%,6%,14%,2%)

$ ./rgb2cmyk.sh "#123456"
(79%,40%,0%,66%)

Answer 10

PHP 7, 123 110 105 bytes

Input as RGB color 100 240 75

$j=max($h=$argv);echo strtr(@(1-$h[1]/$j).",".@(1-$h[2]/$j).",".@(1-$h[3]/$j).",".(1-$j/255),["NAN"=>0]);

Outputs CMYK values as decimal in 0...1 range.

Saved lots of bytes thanks to Titus.

Sample usage:

php -r '$j=max($h=$argv...' 100 240 75
0.58333333333333,0,0.6875,0.058823529411765

php -r '$j=max($h=$argv...' 255 255 255
0,0,0,0

php -r '$j=max($h=$argv...' 0 255 0
1,0,1,0

php -r '$j=max($h=$argv...' 0 0 0 
0,0,0,1

Test online

---

Input as HEX color #123456, 202 bytes

$h=str_split(substr($argv[1],-6),2);$j=max($r=hexdec($h[0]),$g=hexdec($h[1]),$b=hexdec($h[2]));echo z($r,$j),",",z($g,$j),",",z($b,$j),",",1-$j/255;function z($c,$y){return is_nan(@($c/$y))?0:1-$c/$y;}

54 bytes for function to prevent division by zero, probably golfable or removable.

Gets as input RGB color as HEX #123456 and outputs CMYK as decimal in 0...1 range.

Sample usage:

php -r '$h=str_split...' '#000000'
0,0,0,1

php -r '$h=str_split...' '#ffffff'
0,0,0,0

php -r '$h=str_split...' '#123456'
0.7906976744186,0.3953488372093,0,0.66274509803922

php -r '$h=str_split...' '#ffff00'
0,0,1,0

Answer 11

PHP, not competing

I was just too tempted to post my own.

RGB input, 74 bytes

for(;$i++<4;)echo$i<4?($j=max($argv))?1-$argv[$i]/$j:0:1-$j/255,","[$i>3];

or 68 bytes with a trailing comma in the output: remove [$i>3].

Run with php -r '<code>' <red-value> <green-value> <blue-value>.

HEX input, 100 bytes

foreach($a=array_map(hexdec,str_split($argv[1],2))as$c)echo($j=max($a))?1-$c/$j:0,",";echo 1-$j/255;  

Run with php -nr '<code>' RRGGBB.

That approach would take 75 bytes for RGB input:
replace foreach($a=array_map...as$c) with foreach($a=$argv as$c)if($i++).

Answer 12

Hoon, 110 bytes

=>
rs
|*
a/*
=+
[s=(cury sub .1) j=(roll a max)]
(welp (turn a |*(* (s (min .1 (div +< j))))) (s (div j .255)))

Use the single precision floating-point library. Create a new generic function that takes a. Set s to sub curried with .1 for later, and j to folding over a with max.

Map over a by dividing each element with j, finding the minimum of that and 1 to normalize NaN, then subtract 1 with s. Add 1-j/255 to the end of that list.

> =f =>
  rs
  |*
  a/*
  =+
  [s=(cury sub .1) j=(roll a max)]
  (welp (turn a |*(* (s (min .1 (div +< j))))) (s (div j .255)))
> (f (limo ~[.108 .174 .106]))
[i=.3.7931037e-1 t=[i=.0 t=[i=.3.908046e-1 .3.1764704e-1]]]
> (f (limo ~[.0 .0 .0]))
[i=.0 t=[i=.0 t=[i=.0 .1]]]

Answer 13

C, 155 bytes

#define C(x) 1-x/(j>0?j:1)
#define F float
i=0;F j;f(F r,F g,F b){j=(r>g?r:g)>b?(r>g?r:g):b;for(;i++<4;)printf("%f\n",i>1?i>2?i>3?1-j/255:C(b):C(g):C(r));}

I'm trying to figure out how it's possible golf more.

Usage:

#define C(x) 1-x/(j>0?j:1)
#define F float
i=0;F j;f(F r,F g,F b){j=(r>g?r:g)>b?(r>g?r:g):b;for(;i++<4;)printf("%f\n",i>1?i>2?i>3?1-j/255:C(b):C(g):C(r));}
main(){
    f(108,174,106);
}

Output:

0.379310
0.000000
0.390805
0.317647