RGB contrast COLOR Formula

[Arul.rajesh]

Need help to calculate the contrasting colors for given set of RGB values.

For a
<code>
sub contrast()
r=127
g=127
b=127
activecell.font.color=RGB(r,g,b)
new_r=255-r
new_g=255-g
new_b=255-b
activecell.interior.color=RGB(new_r,new_g,new_b)
end sub
</code>
does not help when r,g,b values near 127 or 128 as they are more or less grey.

I need a formula that would give me values of new_r, new_g and new_b that would be in contrast with RGB(r,g,b) for any values of r,g,b from 0-255

 

[JoeMo]

Need help to calculate the contrasting colors for given set of RGB values.

For a
<code>
sub contrast()
r=127
g=127
b=127
activecell.font.color=RGB(r,g,b)
new_r=255-r
new_g=255-g
new_b=255-b
activecell.interior.color=RGB(new_r,new_g,new_b)
end sub
</code>
does not help when r,g,b values near 127 or 128 as they are more or less grey.

I need a formula that would give me values of new_r, new_g and new_b that would be in contrast with RGB(r,g,b) for any values of r,g,b from 0-255

Equal values of r,g and b will produce only shades of gray. Are you looking for a contrast between two shades of gray only or you want color contrast?

 

[circledchicken]

Hi,

Perhaps try adapting the code provided in this article to VBA:
How to Calculate a Complementary Colour / Color | Convert RGB to HSL and HSL to RGB

 

[Arul.rajesh]

I generate r g b values based on the text in a cell, by doing some mathematical calculations on the ascii codes of the characters in the cell. SO that same text has same colors. I need the background color of the cell to be in contrast to the r g b values generated, so that the text is readable.

 

[JoeMo]

I generate r g b values based on the text in a cell, by doing some mathematical calculations on the ascii codes of the characters in the cell. SO that same text has same colors. I need the background color of the cell to be in contrast to the r g b values generated, so that the text is readable.

Are the r g b values you generate always such that r=g=b or can r g and b have different values for the some text?

 

[Arul.rajesh]

here is how I generate RGB
you can use anything, some color that is based on the text


here is what i used
before the next cll i initialize myred, mygre,myblu to zero, i tried adding 40 to red for green, and 100 to red for blue but i can end up with colors near grey anytime.
<code>
prcsss = Left(cll.Value, InStr(cll.Value, " :") - 1)
For i = 1 To Len(prcsss)
myred = Asc(LCase(Left(prcsss, Len(prcsss) - i + 1))) + myred
mygre = mygre + Asc(LCase(Left(prcsss, Len(prcsss) - i + 1))) * Asc(LCase(Left(prcsss, Len(prcsss) - i + 1)))
myblu = myblu + Asc(LCase(Left(prcsss, Len(prcsss) - i + 1)))
Next i



I just converted the RGB to HSL using circledchicken's link. rotated H by 360 and converted back to RGB, WIll post my results in a bit.</code>

 

[Arul.rajesh]

Hi,

Perhaps try adapting the code provided in this article to VBA:
How to Calculate a Complementary Colour / Color | Convert RGB to HSL and HSL to RGB

I converted the entire code to VBA as posted on EasyRGB. The contrasth function inverts the "H" in HSL. but the HSL2RGB function does not even look at H if s=0, so what is the point of inverting H as described in the site. What am I doing wrong?

Function RGB2HSL(r, g, b) As Variant
var_R = (r / 255)  '                     //RGB from 0 to 255
var_G = (g / 255)
var_B = (b / 255)
Set wf = Application.WorksheetFunction


var_Min = wf.Min(var_R, var_G, var_B)  '    //Min. value of RGB
var_Max = wf.Max(var_R, var_G, var_B)   '   //Max. value of RGB
del_Max = var_Max - var_Min           '  //Delta RGB value


L = (var_Max + var_Min) / 2


If (del_Max = 0) Then                     ' //This is a gray, no chroma...


   h = 0                              '  //HSL results from 0 to 1
   S = 0


Else                                   ' //Chromatic data...
   If (L < 0.5) Then
   S = del_Max / (var_Max + var_Min)  '
   Else
   S = del_Max / (2 - var_Max - var_Min)
   End If
   del_R = (((var_Max - var_R) / 6) + (del_Max / 2)) / del_Max
   del_G = (((var_Max - var_G) / 6) + (del_Max / 2)) / del_Max
   del_B = (((var_Max - var_B) / 6) + (del_Max / 2)) / del_Max
   If (var_R = var_Max) Then
   h = del_B - del_G
   ElseIf (var_G = var_Max) Then
   h = (1 / 3) + del_R - del_B
   ElseIf (var_B = var_Max) Then
   h = (2 / 3) + del_G - del_R
    End If
   If (h < 0) Then h = h + 1
   If (h > 1) Then h = h - 1
End If
RGB2HSL = Array(h, S, L)
End Function

Function hsl2rgb(h, S, L)
If (S = 0) Then  '                       //HSL from 0 to 1


   r = L * 255                     ' //RGB results from 0 to 255
   g = L * 255
   b = L * 255
Else


   If (L < 0.5) Then
     var_2 = L * (1 + S)
   Else
     var_2 = (L + S) - (S * L)
   End If
     var_1 = 2 * L - var_2


   r = 255 * Hue_2_RGB(var_1, var_2, h + (1 / 3))
   g = 255 * Hue_2_RGB(var_1, var_2, h)
   b = 255 * Hue_2_RGB(var_1, var_2, h - (1 / 3))
End If
   hsl2rgb = RGB(r, g, b)
End Function
Function Hue_2_RGB(v1, v2, vH)              ' //Function Hue_2_RGB


   If (vH < 0) Then vH = vH + 1
   If (vH > 1) Then vH = vH - 1
   If ((6 * vH) < 1) Then
   Hue_2_RGB = (v1 + (v2 - v1) * 6 * vH)
   Exit Function
   End If
   If ((2 * vH) < 1) Then
   Hue_2_RGB = (v2)
   Exit Function
   End If
   If ((3 * vH) < 2) Then
   Hue_2_RGB = (v1 + (v2 - v1) * ((2 / 3) - vH) * 6)
   Exit Function
   End If
Hue_2_RGB = v1
End Function


Function contrasth(h As Variant)
h = h + 0.5
If h > 1 Then h = h - 1
contrasth = h
End Function

 

[Arul.rajesh]

The code that i used to call these functions is as below, but grey background returns grey text

Option Base 1

Sub ColorActiveCell()
Call colorer(ActiveCell, 127, 127, 127)
End Sub



Sub colorer(cl As Range, r As Integer, g As Integer, b As Integer)cl.Interior.Color = RGB(r, g, b)
myarr = RGB2HSL(r, g, b)
h = contrasth(myarr(1))
S = myarr(2)
L = myarr(3)
inverted = hsl2rgb(h, S, L)
cl.Font.Color = inverted
End Sub

 

[Rick Rothstein]

Here is a function I have posted in the past...

Function TextColorToUse(BackColor As Long) As Long
  TextColorToUse = -vbWhite * (77 * (BackColor Mod &H100) + 151 * ((BackColor \ &H100) _
                   Mod &H100) + 28 * ((BackColor \ &H10000) Mod &H100) < 32640)
End Function

If you have your values as separate RGB values, then just use the RGB function as the argument. For example...

R = 012
G = 123
B = 234
NewFontColor = TextColorToUse(RGB(R, G, B))

 

[Arul.rajesh]

Thanks for that elegant function Rick....Thank you circled chicken, JoeMo for your help.