RGB values of visible spectrum

Question

I need an algorithm or function to map each wavelength of visible range of spectrum to its equivalent RGB values. Is there any structural relation between the RGB System an

Answer 1

VBA code is derived from Approximate "RGB values for Visible Wavelengths" by Dan Bruton (astro@tamu.edu). Link to his original Fortran code: http://www.physics.sfasu.edu/astro/color/spectra.html Spectra program: http://www.efg2.com/Lab/ScienceAndEngineering/Spectra.htm

Sub Wavelength_To_RGB()

'Purpose: Loop thru the wavelengths in the visible spectrum of light
'         and output the RGB values and colors to a worksheet.
'         Wavelength range: 380nm and 780nm

Dim j As Long, CellRow As Long
Dim R As Double, G As Double, B As Double
Dim iR As Integer, iG As Integer, iB As Integer
Dim WL As Double
Dim Gamma As Double
Dim SSS As Double


Gamma = 0.8
CellRow = 1

For j = 380 To 780

  WL = j

  Select Case WL

  Case 380 To 440
      R = -(WL - 440#) / (440# - 380#)
      G = 0#
      B = 1#
  Case 440 To 490
      R = 0#
      G = ((WL - 440#) / (490# - 440#))
      B = 1#
  Case 490 To 510
      R = 0#
      G = 1#
      B = (-(WL - 510#) / (510# - 490#))
  Case 510 To 580
      R = ((WL - 510#) / (580# - 510#))
      G = 1#
      B = 0#
  Case 580 To 645
      R = 1#
      G = (-(WL - 645#) / (645# - 580#))
      B = 0#
  Case 645 To 780
      R = 1#
      G = 0#
      B = 0#
  Case Else
      R = 0#
      G = 0#
      B = 0#
  End Select

  'LET THE INTENSITY SSS FALL OFF NEAR THE VISION LIMITS
  If WL > 700 Then
     SSS = 0.3 + 0.7 * (780# - WL) / (780# - 700#)
  ElseIf WL < 420 Then
     SSS = 0.3 + 0.7 * (WL - 380#) / (420# - 380#)
  Else
     SSS = 1#
  End If

  'GAMMA ADJUST
  R = (SSS * R) ^ Gamma
  G = (SSS * G) ^ Gamma
  B = (SSS * B) ^ Gamma

  'Multiply by 255
  R = R * 255
  G = G * 255
  B = B * 255

  'Change RGB data type from Double to Integer.
  iR = CInt(R)
  iG = CInt(G)
  iB = CInt(B)

  'Output to worksheet
  Cells(CellRow, 1).Interior.Color = RGB(iR, iG, iB)
  Cells(CellRow, 2) = WL
  Cells(CellRow, 3) = "(" & iR & "," & iG & "," & iB & ")"
  CellRow = CellRow + 1

Next j


End Sub