NewsForumsCodeLogsGallerySpecsSearch

Code archives/Graphics/Color space conversion

This code has been declared by its author to be Public Domain code.

Download source code

Color space conversion by Pineapple2012
Convert colors to and from RGB, CMY, CMYK, HSV, HSL, HCL, YIQ, YUV, CIE XYZ, and CIE L*ab 
' 	--+-----------------------------------------------------------------------------------------+--
'	  |   This code was originally written by Sophie Kirschner (sophiek@pineapplemachine.com)   |  
' 	  | It is released as public domain. Please don't interpret that as liberty to claim credit |  
' 	  |   that isn't yours, or to sell this code when it could otherwise be obtained for free   |  
'	  |                because that would be a really shitty thing of you to do.                |
' 	--+-----------------------------------------------------------------------------------------+--


' Usage:
'  1:
'   Use FloatRGB:Float[] ( red:Int , green:Int, blue:Int ) to convert your
'   color to a form that the conversion functions can best work with.
'  2:
'   Call your function rgbto___:Float[] ( ___:Float[] ) using that returned
'   value to get it in your desired color space. (Where "___" is the color
'   space you want to convert to)
'  3:
'   Modify the values in that returned array however you like
'  4:
'   Use SetColorRGB ( rgb:Float[] ) to set it as a color, or 
'   ___torgb:Float[] to conver it back to the rgb colorspace and then
'   IntRGB:Int[] ( rgb:Float[] ) or ByteRGB:Byte[] ( rgb:Float[] ) or
'   GetR:Int( rgb:Float[] ) and GetG:Int( rgb:Float[] ) and
'   GetB:Int( rgb:Float[] ) to get the new red,green,blue values
'  Ranges:
'   RGB: [0,1]
'   CMY: [0,1]
'   CMYK: [0,1]
'   HSV: [0,1]
'   HSL: [0,1]
'   HCL: [0,1]
'   YIQ: [-1,1]
'   YUV: [-1,1]
'   XYZ: [0,1]
'   L*ab: [0,100] for L*, a and b are theoretically unbounded (I think, 
'                 I could very well be interpreting this stuff wrong)


SuperStrict

' example program
Rem 
AppTitle="Color spaces"
Graphics 320,240
Local val#[]=[.5,.5,.5],s#=0.005
Repeat
	setcolorrgb hsvtorgb(val)
	DrawRect 0,0,64,240
	setcolorrgb hsltorgb(val)
	DrawRect 64,0,64,240
	setcolorrgb hcltorgb(val)
	DrawRect 128,0,64,240
	setcolorrgb xyztorgb(val)
	DrawRect 192,0,64,240
	setcolorrgb cmytorgb(val)
	DrawRect 256,0,64,240
	
	DrawText_ "hsv",2,220
	DrawText_ "hsl",66,220
	DrawText_ "hcl",130,220
	DrawText_ "xyz",194,220
	DrawText_ "cmy",258,220
	
	DrawText_ "value: "+Left(val[0],5)+","+Left(val[1],5)+","+Left(val[2],5),2,0
	DrawText_ "a,z,s,x,d,c keys to alter the values",2,16
	
	If KeyDown(key_a) Then val[0]:+s
	If KeyDown(key_z) Then val[0]:-s
	If KeyDown(key_s) Then val[1]:+s
	If KeyDown(key_x) Then val[1]:-s
	If KeyDown(key_d) Then val[2]:+s
	If KeyDown(key_c) Then val[2]:-s
	For Local x%=0 To 2
		If val[x]>1 val[x]=1
		If val[x]<0 val[x]=0
	Next
	Flip
Until KeyDown(27) Or AppTerminate()

Function DrawText_(str$,x%,y%)
	SetColor 0,0,0
	DrawText str,x,y+1
	DrawText str,x+1,y
	DrawText str,x,y-1
	DrawText str,x-1,y
	DrawText str,x+1,y+1
	DrawText str,x-1,y-1
	DrawText str,x+1,y-1
	DrawText str,x-1,y+1
	SetColor 255,255,255
	DrawText str,x,y
End Function
End Rem

' For your convenience, SetColor for an array containing 3 floats indicating rgb
Function SetColorRGB(rgb#[])
	SetColorRGBv rgb[0],rgb[1],rgb[2]
End Function

' SetColor for 3 floats indicating rgb
Function SetColorRGBv(br#,bg#,bb#)
	Local r%=br*255,g%=bg*255,b%=bb*255
	If r<0 r=0
	If g<0 g=0
	If b<0 b=0
	If r>255 r=255
	If g>255 g=255
	If b>255 b=255
	SetColor r,g,b
End Function

' Turn a float array indicating RGB into a byte array
Function ByteRGB@[](rgb#[])
	Return [Byte(rgb[0]*255),Byte(rgb[1]*255),Byte(rgb[2]*255)]
End Function

' Turn a float array indicating RGB into an int array
Function IntRGB%[](rgb#[])
	Return [Int(rgb[0]*255),Int(rgb[1]*255),Int(rgb[2]*255)]
End Function

' Turn rgb into a float array
Function FloatRGB#[](red%,green%,blue%)
	Return [red/255.0,green/255.0,blue/255.0]
End Function

Function FloatARGB#[](argb%)
	Return [((argb Shr 16)&$ff)/255.0,((argb Shr 8)&$ff)/255.0,(argb&$ff)/255.0]
End Function

' Get individual channels from float array
Function GetR%(rgb#[])
	Return rgb[0]*255
End Function
Function GetG%(rgb#[])
	Return rgb[0]*255
End Function
Function GetB%(rgb#[])
	Return rgb[0]*255
End Function

' the following code was adapted from the examples found at:
' http://easyrgb.com/index.php?X=MATH&H=02#text2

' observer = 2 degrees, illuminant = D65
Const refx#=95.047
Const refy#=100.0
Const refz#=108.883

' assumes rgb in the range [0,1]
' returns xyz in the range [0,1]
Function rgbtoxyz#[](rgb#[])
	Local r#=rgb[0],g#=rgb[1],b#=rgb[2]
	If(r>0.04045) Then 
		r=((r+0.055)/1.055)^2.4
	Else
		r:/12.92
	EndIf
	If(g>0.04045) Then 
		g=((g+0.055)/1.055)^2.4
	Else
		g:/12.92
	EndIf
	If(b>0.04045) Then 
		b=((b+0.055)/1.055)^2.4
	Else
		b:/12.92
	EndIf
	r:*100
	g:*100
	b:*100
	Return [(r*0.4124+g*0.3576+b*0.1805)/refx,(r*0.2126+g*0.7152+b*0.0722)/refy,(r*0.0193+g*0.1192+b*0.9505)/refz]
End Function
' assumes xyz in the range [0,1]
' returns rgb in the range [0,1]
Function xyztorgb#[](xyz#[])
	Local x#=xyz[0]*refx/100.0,y#=xyz[1]*refy/100.0,z#=xyz[2]*refz/100.0
	Local r#=x* 3.2406+y*-1.5372+z*-0.4986
	Local g#=x*-0.9689+y* 1.8758+z* 0.0415
	Local b#=x* 0.0557+y*-0.2040+z* 1.0570
	If r>0.0031308 Then
		r=1.055*(r^(0.416666667))-.055
	Else
		r:*12.92
	EndIf
	If g>0.0031308 Then
		g=1.055*(g^(0.416666667))-.055
	Else
		g:*12.92
	EndIf
	If b>0.0031308 Then
		b=1.055*(b^(0.416666667))-.055
	Else
		b:*12.92
	EndIf
	Return [r,g,b]
End Function
' assumes xyz in the range [0,1]
' returns l*ab in a very varying range
Function xyztolab#[](xyz#[])
	Local x#=xyz[0],y#=xyz[1],z#=xyz[2]
	If(x>0.008856) Then
		x=x^0.333333333
	Else
		x=(x*7.787)+0.137931034
	EndIf
	If(y>0.008856) Then
		y=y^0.333333333
	Else
		y=(y*7.787)+0.137931034
	EndIf
	If(z>0.008856) Then
		z=z^0.333333333
	Else
		z=(z*7.787)+0.137931034
	EndIf
	Return [116*y-16,500*(x-y),200*(y-z)]
End Function
' assumes l*ab in a very varying range
' assumes xyz in the range [0,1]
Function labtoxyz#[](lab#[])
	Local y#=(lab[0]+16)/116.0
	Local x#=lab[1]/500.0+y
	Local z#=y-lab[2]/200.0
	If x^3>.008856 Then
		x=x^3
	Else
		x=(x-0.137931034)/7.787
	EndIf
	If y^3>.008856 Then
		y=y^3
	Else
		y=(y-0.137931034)/7.787
	EndIf
	If z^3>.008856 Then
		z=z^3
	Else
		z=(z-0.137931034)/7.787
	EndIf
	Return [x,y,z]
End Function
' assumes rgb in the range [0,1]
' returns l*ab in a very varying range
Function rgbtolab#[](rgb#[])
	Return xyztolab(rgbtoxyz(rgb))
End Function
' assumes l*ab in a very varying range
' returns rgb in the range [0,1]
Function labtorgb#[](lab#[])
	Return xyztorgb(labtoxyz(lab))
End Function
' assumes rgb in the range [0,1]
' returns cmy in the range [0,1]
Function rgbtocmy#[](rgb#[])
	Return [1-rgb[0],1-rgb[1],1-rgb[2]]
End Function
' assumes cmy in the range [0,1]
' returns rgb in the range [0,1]
Function cmytorgb#[](cmy#[])
	Return [1-cmy[0],1-cmy[1],1-cmy[2]]
End Function
' assumes cmy in the range [0,1]
' returns cmyk in the range [0,1]
Function cmytocmyk#[](cmy#[])
	Local c#=cmy[0],m#=cmy[1],y#=cmy[2]
	Local k#=1
	If c<k Then k=c
	If m<k Then k=m
	If y<k Then k=y
	If k=1 Then Return [0.0,0.0,0.0,k]
	Local k1#=1-k
	Return [(c-k)/k1,(m-k)/k1,(y-k)/k1,k]
End Function
' assumes cmyk in the range [0,1]
' returns cmy in the range [0,1]
Function cmyktocmy#[](cmyk#[])
	Local k1#=1-cmyk[3]
	Return [cmyk[0]*k1+cmyk[3],cmyk[1]*k1+cmyk[3],cmyk[2]*k1+cmyk[3]]
End Function
' assumes rgb in the range [0,1]
' returns cmyk in the range [0,1]
Function rgbtocmyk#[](rgb#[])
	Return cmytocmyk(rgbtocmy(rgb))
End Function
' assumes cmyk in the range [0,1]
' returns rgb in the range [0,1]
Function cmyktorgb#[](cmyk#[])
	Return cmytorgb(cmyktocmy(cmyk))
End Function

' the following code was adapted from the examples found at:
' http://mjijackson.com/2008/02/rgb-to-hsl-and-rgb-to-hsv-color-model-conversion-algorithms-in-javascript

' assumes rgb in the range [0,1]
' returns hsl in the range [0,1]
Function rgbtohsl#[](rgb#[])
	Local r#=rgb[0],g#=rgb[1],b#=rgb[2]
	Local hsl#[]=New Float[3]
	Local ax#=Max(Max(r,g),b),in#=Min(Min(r,g),b)
	hsl[2]=(ax+in)/2.0
	If(ax=in) Then Return hsl
	Local d#=ax-in
	If hsl[2]>.5 Then hsl[1]=d/(2.0-ax-in) Else hsl[1]=d/(ax+in)
	Select ax
		Case r
			Local gv%=0
			If g<b Then gv=6
			hsl[0]=(g-b)/d+gv
		Case g
			hsl[0]=(b-r)/d+2
		Case b
			hsl[0]=(r-g)/d+4
	End Select
	hsl[0]:/6.0
	Return hsl
End Function
' assumes hsl in the range [0,1]
' returns rgb in the range [0,1]
Function hsltorgb#[](hsl#[])
	Local h#=hsl[0],s#=hsl[1],l#=hsl[2]
	If s=0 Then Return [l,l,l]
	Local q#
	If l<.5 Then q=l*(1+s) Else q=(l+s-l*s)
	Local p#=2*l-q
	Return [_huetorgb(p,q,h+0.333333333),_huetorgb(p,q,h),_huetorgb(p,q,h-0.333333333)]
End Function
Function _huetorgb#(p#,q#,t#)
	If t<0 t:+1
	If t>1 t:-1
	If t<0.166666667 Return p+(q-p)*6*t
	If t<0.5 Return q
	If t<0.666666667 Return p+(q-p)*(0.666666667-t)*6
	Return p
End Function
' assumes rgb in the range [0,1]
' returns hsv in the range [0,1]
Function rgbtohsv#[](rgb#[])
	Local r#=rgb[0],g#=rgb[1],b#=rgb[2]
	Local hsv#[]=New Float[3]
	Local ax#=Max(Max(r,g),b),in#=Min(Min(r,g),b)
	hsv[2]=ax
	Local d#=ax-in
	hsv[1]=0
	If ax<>0 Then hsv[1]=d/ax
	If(ax=in) Then hsv[0]=0;Return hsv
	Select ax
		Case r
			Local gv%=0
			If g<b Then gv=6
			hsv[0]=(g-b)/d+gv
		Case g
			hsv[0]=(b-r)/d+2
		Case b
			hsv[0]=(r-g)/d+4
	End Select
	hsv[0]:/6.0
	Return hsv
End Function
' assumes hsv in the range [0,1]
' returns rgb in the range [0,1]
Function hsvtorgb#[](hsv#[])
	Local h#=hsv[0],s#=hsv[1],v#=hsv[2]
	Local h6#=h*6
	Local i%=h6
	Local f#=h6-i
	Local p#=v*(1-s)
	Local q#=v*(1-f*s)
	Local t#=v*(1-(1-f)*s)
	Select i Mod 6
		Case 0 Return [v,t,p]
		Case 1 Return [q,v,p]
		Case 2 Return [p,v,t]
		Case 3 Return [p,q,v]
		Case 4 Return [t,p,v]
		Case 5 Return [v,p,q]
	End Select
	Return [0.0,0.0,0.0]
End Function

' the following code was derived from the information found at:
' http://en.wikipedia.org/wiki/HSL_and_HSV#From_luma.2Fchroma.2Fhue

Const _b_r#=.3,_b_g#=.59,_b_b#=.11

' assumes hcl in the range [0,1]
' returns rgb in the range [0,1]
Function hcltorgb#[](hcl#[])
	Local h#=hcl[0]*6,c#=hcl[1]
	Local x#=c*(1-Abs((h Mod 2)-1))
	Local rgb#[]
	If 0<=h And h<1
		rgb=[c,x,0.0]
	ElseIf 1<=h And h<2
		rgb=[x,c,0.0]
	ElseIf 2<=h And h<3
		rgb=[0.0,c,x]
	ElseIf 3<=h And h<4
		rgb=[0.0,x,c]
	ElseIf 4<=h And h<5
		rgb=[x,0.0,c]
	ElseIf 5<=h And h<=6
		rgb=[c,0.0,x]
	Else
		rgb=[0.0,0.0,0.0]
	EndIf
	Local m#=hcl[2]-(_b_r*rgb[0]+_b_g*rgb[1]+_b_b*rgb[2])
	rgb[0]:+m
	rgb[1]:+m
	rgb[2]:+m
	Return rgb
End Function
' assumes rgb in the range [0,1]
' returns hcl in the range [0,1]
Function rgbtohcl#[](rgb#[])
	Local r#=rgb[0],g#=rgb[1],b#=rgb[2]
	Local hcl#[]=New Float[3]
	Local m#=Max(Max(r,g),b)
	hcl[1]=m-Min(Min(r,g),b)
	If hcl[1]=0 Then
		hcl[0]=0
	ElseIf m=r
		hcl[0]=((g-b)/hcl[1]) Mod 6
	ElseIf m=g
		hcl[0]=((b-r)/hcl[1])+2
	ElseIf m=b
		hcl[0]=((r-g)/hcl[1])+4
	EndIf
	hcl[0]:/6.0
	hcl[2]=_b_r*r+_b_g*g+_b_b*b
	Return hcl
End Function

' assumes rgb in the range [0,1]
' returns yiq in the range [-1,1]
Function rgbtoyiq#[](rgb#[])
	Local r#=rgb[0],g#=rgb[1],b#=rgb[2]
	Local yiq#[]=New Float[3]
	yiq[0]=0.299000*r + 0.587000*g + 0.114000*b
	yiq[1]=0.595716*r - 0.274453*g - 0.321264*b
	yiq[2]=0.211456*r - 0.522591*g + 0.311350*b
	Return yiq
End Function

' assumes yiq in the range [-1,1]
' returns rgb in the range [0,1]
Function yiqtorgb#[](yiq#[])
	Local y#=yiq[0],i#=yiq[1],q#=yiq[2]
	Local rgb#[]=New Float[3]
	rgb[0]=y + 0.9563*i + 0.6210*q
	rgb[1]=y - 0.2721*i - 0.6474*q
	rgb[2]=y - 1.1070*i + 1.7046*q
	Return rgb
End Function

' assumes rgb in the range [0,1]
' returns yuv in the range [-1,1]
Const yuv_uconst#=1.0/0.436
Const yuv_vconst#=1.0/0.615
Function rgbtoyuv#[](rgb#[])
	Local r#=rgb[0],g#=rgb[1],b#=rgb[2]
	Local yuv#[]=New Float[3]
	yuv[0]=(0.299*r + 0.587*g + 0.114*b)
	yuv[1]=(0.492*(b-yuv[0]))*yuv_uconst
	yuv[2]=(0.877*(r-yuv[0]))*yuv_vconst
	yuv[0]=yuv[0]*2-1
	Return yuv
End Function

' assumes yuv in the range [-1,1]
' returns rgb in the range [0,1]
Function yuvtorgb#[](yuv#[])
	Local y#=(yuv[0]+1)/2.0,u#=yuv[1]/yuv_uconst,v#=yuv[2]/yuv_vconst
	Local rgb#[]=New Float[3]
	rgb[0]=y + 1.140*v
	rgb[1]=y - 0.395*u - 0.581*v
	rgb[2]=y + 2.032*u
	Return rgb
End Function

Comments

Pineapple2012
2 July, 2012: Added support for the YIQ and YUV color spaces


Streaksy2012
Very good. :D


Midimaster2012
It is not as easy as the code will say us...

the problem is that it is not only a mathematical formula to change from RGB to CMYK:

Function rgbtocmy#[](rgb#[])
	Return [1-rgb[0],1-rgb[1],1-rgb[2]]
End Function


There are RGB constellations, which cannot transformed in an valid CMYK color space and this formula will cause problems in the print office. Your picture will change to PURPLE in all DARK BLUE areas.

So,... a real good code should warn when leaving the CMYK color space.


Pineapple2013
Midimaster: I used http://easyrgb.com/index.php?X=MATH&H=11#text11 as a reference, assuming that it was a reasonably accurate conversion. Do any better algorithms exist?


Midimaster2013
yes and no

a simple algo like yours does not respect the limitations of RGB and CMYK color spaces. The conversion will change colors.

Read this:

http://www.printingforless.com/rgb-cmyk.html

there are a lot of advises which show, that the conversion is not that simple.

"We recommend a CMYK value of 100-65-0-0 to get a nice clean blue"


http://www.colormatch.de/



In theory the "full blue" RGB 0-0-255 would result in CMYK 1-1-0-0. But if you print this color it would be "purple".

1-0.6-0-0 is the best "blue" you can get in CMYK. But this is based on experience. So how could a formula look like? There are better algo's: Adobe Photoshop knows how to convert, but they do not tell anything about the formula.


Code Archives Forum