CONTRAST

[lrobbo314]

CONTRAST returns the contrast ratio between 2 colors. The range of values returned is from 1-21 with 21 being the highest contrast value.

=LAMBDA(
    color1,
    color2,
        LET(
            a,color1,
            b,color2,
            d,.05,
            f,LAMBDA(rgb,SUM(MAP(rgb/255,LAMBDA(v,IF(v<0.03928,v/12.92,((v+0.055)/1.055)^2.4)))*{0.2126,0.7152,0.0722})),
            x,f(a),
            y,f(b),
                (MAX(x,y)+d)/(MIN(x,y)+d)
        )
)

CONTRAST
	A	B	C	D	E	F	G	H
1	R	G	B
2	0	0	0			7.192099		Happy Halloween
3	255	103	0
4
5
6	Text	17, 42, 70	Example	Contrast		Good Contrast
7	Background	172, 200, 229		8.415388931
8
9
10	Text	31, 189, 34	Example	Contrast		Bad Contrast
11	Background	187, 172, 230		1.214846767
Sheet1

Cell Formulas
Range	Formula
F2	F2	=CONTRAST(A2:C2,A3:C3)
A2:C3	A2	=SPLITBYDELIMITER(Color(D2,2),", ",)
B6	B6	=HXRGB("112a46")
B7	B7	=HXRGB("acc8e5")
D7,D11	D7	=CONTRAST(SPLITBYDELIMITER(B6,", ",),SPLITBYDELIMITER(B7,", ",))
B10	B10	=HXRGB("1fbd22")
B11	B11	=HXRGB("bbace6")
Dynamic array formulas.

Extras:

Some of the other formulas in the table above include:

SPLITTEXTBYDELIMITER

This function is credited to @Xlambda. It is his ATEXTSPLIT function that I wrote over and over again to figure it out.

=LAMBDA(
    text,delim,shrink,
        LET(h,"Æ",d,"ᐃ",
        a,SUBSTITUTE(text,delim,h),
        b,IF(shrink,a,SUBSTITUTE(SUBSTITUTE(TRIM(SUBSTITUTE(SUBSTITUTE(a," ",d),h," "))," ",h),d," ")),
        n,LEN(b)-LEN(SUBSTITUTE(b,h,""))+1,
        c,MAX(n),sc,SEQUENCE(,c),
        x,SEARCH(d,SUBSTITUTE(h&b,h,d,sc)),
        y,SEARCH(d,SUBSTITUTE(b&h,h,d,sc)),
            IFERROR(MID(b,x,y-x),"")
        )
)

HXRGB

I wrote this one to convert a hex string to RGB values.

=LAMBDA(
    text,
        MAP(text,
            LAMBDA(h,TEXTJOIN(", ",,HEX2DEC(MID(h,{1;3;5},2))))
        )
)

COLOR

This is a VBA function that I got from the forum. Can't remember where it came from to give credit. There are a bunch of versions of this around. This function returns the color of the background of a cell. It will return HEX, RGB, COLORINDEX, or COLOR, depending on the formatType argument.

Function Color(rng As Range, Optional formatType As Integer = 0) As Variant
    Dim colorVal As Variant
    colorVal = rng.Cells(1, 1).Interior.Color
    Select Case formatType
        Case 1
            Color = WorksheetFunction.Dec2Hex(colorVal, 6)
        Case 2
            Color = (colorVal Mod 256) & ", " & ((colorVal \ 256) Mod 256) & ", " & (colorVal \ 65536)
        Case 3
            Color = rng.Cells(1, 1).Interior.ColorIndex
        Case Else
            Color = colorVal
    End Select
End Function