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ContrastText ( foregroundText ; bgRedPercent ; bgGreenPercent ; bgBluePercen

Colors foregroundText black or white as appropriate for the specified background color.

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Joe Rovang - Show more from this author

  Function definition: (Copy & paste into FileMaker's Edit Custom Function window)

Let ( [ /* Luminance values below range from 0 to 1, where 1 is perceived as being as luminous as full-intensity white, and 0 is black. Preferred levels may vary by individual, particularly those with any degree of color-blindness. */ RedLum = (.35) ; // How luminous is the color red? (default: .35) GreenLum = (.6) ; // How luminous is the color green? (default: .6) BlueLum = (.13) ; // How luminous is the color blue? (default: .13) bgRed = GetAsNumber ( bgRedPercent ) ; bgGreen = GetAsNumber ( bgGreenPercent ) ; bgBlue = GetAsNumber ( bgBluePercent ) ; Lum = Min ( ( bgRed * RedLum ) + ( bgGreen * GreenLum ) + ( bgBlue * BlueLum ) ; 1 ) ; LumCutoff = (.46) ; // Above what luminance value should white text become black? (default: .46; preferred level may vary according to monitor's brightness setting) ColorBlack = RGB ( 0 ; 0 ; 0 ) ; ColorWhite = RGB ( 255 ; 255 ; 255 ) ] ; Case ( ( bgRed ≥ 0 ) and ( bgRed ≤ 1 ) and ( bgGreen ≥ 0 ) and ( bgGreen ≤ 1 ) and ( bgBlue ≥ 0 ) and ( bgBlue ≤ 1 ) ; TextColor ( foregroundText ; Case ( Lum > LumCutoff ; ColorBlack ; ColorWhite ) ) ; foregroundText ) ) Click to copy

Parameters:
foregroundText
bgRedPercent
bgGreenPercent
bgBluePercent

This function will color foregroundText black or white, depending on the background color specified using the respective percentage parameters. (Color percentages must be specified as values between 0 and 1.)

This could come in handy if you have a background color generated dynamically (in my solution, I did this using a TextColor-based calculation field set to output a block character at a very large font size). If your colors are generated by HSB (hue/saturation/brightness, also known as HSV/HSL), try my HSBtoRGB() function to convert those values to RGB percentages as input parameters for this function.

Feel free to adjust the luminance values embedded in the function, especially if your color perception or monitor settings are atypical!

 

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