Splitting long-integer RGB values into R, G, and B

[Jonathan States]

Graphics aren't my thing, I'm afraid. Actually, nothing is really "my thing," when it comes to programming.

I dug around a bit, and found that the PBCC4.04 function RGB() does not have a true inverse function; there is a BGR() function, but that does something different.

Those of you who do graphics programs probably know about RGB():

long RGB(r, g, b)
where r, g, and b are (integer?) color values from 0 to 255.

What I need is a function that takes a long integer (that is an RGB color value) and splits it back into its constituent r, g, and b values, which I can then manipulate and do whatever with.

Is there actually a formula for this out there already, or is this going to involve some code breaking? I printed out the value of the RGB() function six times with various values for the r, g, and b values to see if there was an obvious pattern, but there isn't as far as I can see:

RGB(0,0,0)=0 (this doesn't defy logic)
RGB(1,1,1)=65793 (OK, a bit unexpected)
RGB(10,10,10)=657930 (very unexpected)
RGB(12,34,56)=3678732 (not very enlightening)
RGB(10,20,30)=1971210 (ditto)
RGB(13,25,46)=3021069 (still in the dark)

So there we have it. I'm hoping that someone else has run into this before; otherwise I may have to write a program to crack the pattern (if there is one), which is going to be painful.

Any thoughts?

[Mark Hunter]

Run this, enter either a decimal number or a hexidecimal preceeded by &h

Function PBMain
 Local c$
 Local col As Long
 Local Bcol As Long
 Local Gcol As Long
 Local Rcol As Long
 Do
  Cls
  Input "Type color code:  ", c$
  If c$ = "" Then Exit Function
  col = Val(c$)
  Print " ";c$
  Print col
  Print " &h";Hex$(col)
  '-------------------------------------------
  Bcol = col And &h0000FF
  Gcol = col And &h00FF00 :Shift Right Gcol,8
  Rcol = col And &hFF0000 :Shift Right Rcol,16
  '-------------------------------------------
  Print Rcol, Gcol, Bcol
  Print " ";Hex$(Rcol),Hex$(Gcol),Hex$(Bcol)
  WaitKey$
 Loop
End Function

[Dale Yarker]

Mark,

Red is in byte 0, Green in byte 1, and Blue in byte 2.

'this:
'-------------------------------------------
  Bcol = col And &h0000FF
  Gcol = col And &h00FF00 :Shift Right Gcol,8
  Rcol = col And &hFF0000 :Shift Right Rcol,16
'-------------------------------------------
'should be:
'-------------------------------------------
  Rcol = col And &h0000FF
  Gcol = col And &h00FF00 :Shift Right Gcol,8
  Bcol = col And &hFF0000 :Shift Right Bcol,16
'-------------------------------------------

Jonathan,

To work with the red, green and blue by name

type RGBType
  R as byte
  G as byte
  B as byte
  nu as byte
end type
union RGBUnion
  byts as RGBType
  lg as long
end union

'in code:
local col as RGBUnion
'set red to 128
col.byts.R = 128
'set a console's foreground to col and background to white
color col.lg, &hFFFFFF

Cheers,

[Dave Biggs]

Another example

#INCLUDE "WIN32API.INC"
 
Sub IntegerToRGB (ByVal IntegerValue As Long, lRed As Long, lGreen As Long, lBlue As Long)
 
  lRed = Val("&h" + Mid$(Hex$(IntegerValue,6),5,2))
  lGreen = Val("&h" + Mid$(Hex$(IntegerValue,6),3,2))
  lBlue = Val("&h" + Mid$(Hex$(IntegerValue,6),1,2))
 
End Sub 
'------------------/IntegerToRGB
 
Function PbMain()
 Local IntegerValue, r, b, g As Long 
 Local lRed, lGreen, lBlue As Long 
 Local sMsg, sTitle As String 
 
  r = 13 : g = 25 : b = 46              ' <-test values
  IntegerValue = RGB(r,g,b)
 
  IntegerToRGB (IntegerValue, lRed, lGreen, lBlue) 
 
  sMsg = "Red"+$Tab+  str$(lRed)+$CR+ _
         "Green"+$Tab+str$(lGreen)+$CR+ _
         "Blue"+$Tab+ str$(lBlue)
  sTitle = str$(RGB(r,g,b))
  MessageBox 0, ""+sMsg, "Int Value"+sTitle ,%MB_ICONINFORMATION OR %MB_OK
 
End Function
'------------------/PBMain

[Dale Yarker]

Whoops, Jonathan asked for "...splits it back into its constituent ..." and I only showed a different way to set it.

Add to above:

local Rcol as long
local Bcol as long
local Gcol as long
'
Rcol = col.byts.R
Gcol = col.byts.G
Bcol = col.byts.B

You can also get to separate colors within a long color value by a byte pointer.
local pColor as byte pointer
pColor = varptr(col)
Rcol = @pColor 'at pointer + 0
incr pColor
Gcol = @pColor 'at pointer + 1
incr pColor
Bcol = @pColor 'at pointer + 2

Lots of ways to "skin the cat" in programming.

What seems like wierd numbers (like "RGB(10,10,10)=657930 (very unexpected)") is a consequence of viewing as decimal. In this case:
657930 = 10 + (10 * 256) + (10 * 65536)

C U L -

[Adam J. Drake]

Some other possibilities: http://www.powerbasic.com/support/pb...ad.php?t=13159

[Pierre Bellisle]

When going the UNION way,
If one want to simplify it a little further
then using a type without a variable name give a little plus.
PowerBASIC describe it as "Structure within structure"

 
#COMPILE EXE '#Win 8.04#
#DIM ALL
#INCLUDE "WIN32API.INC" '#2005-01-27#
 
TYPE ColorBytes
  R AS BYTE 'Red
  G AS BYTE 'Green
  B AS BYTE 'Blue
  A AS BYTE 'Alpha
END TYPE
 
UNION ColorUnion
  RGB AS DWORD
  ColorBytes '<- Look ma, no var, just the TYPE
END UNION    '   so MyColor.R could be used instead of MyColor.SomeVar.R
 
'______________________________________________________________________________
 
FUNCTION PBMAIN() AS LONG
 LOCAL MyColor AS ColorUnion
 
 MyColor.RGB = RGB(1, 2, 0)
 MyColor.B   = 3
 
 MessageBox %HWND_DESKTOP, "RGB" & $TAB & HEX$(MyColor.RGB, 8) & $CRLF & _
                           "R"   & $TAB & HEX$(MyColor.R)      & $CRLF & _
                           "G"   & $TAB & HEX$(MyColor.G)      & $CRLF & _
                           "B"   & $TAB & HEX$(MyColor.B), _
                           "RGB and R, G, B", %MB_ICONINFORMATION OR %MB_OK
 
END FUNCTION
'______________________________________________________________________________

[Michael Mattias]

FUNCTION PbMain() AS LONG

  CALL TestRgbMacros()

END FUNCTION


MACRO mGetRed   (Rgbvalue)  = Rgbvalue AND &h0FF
MACRO mGetGreen (rgbvalue)  = (Rgbvalue AND &h0FF00)   \ &h100
MACRO mGetBlue  (rgbvalue)  = (rgbvalue AND &h0FF0000) \ &h10000


FUNCTION TestRGBMACROS () AS LONG

    LOCAL R AS BYTE, G AS BYTE, B AS BYTE, rgbvalue AS LONG
    LOCAL S AS STRING

    R = 100
    G = 200
    B = 12

    rgbvalue = RGB(R,G,B)

    S = USING$ ("Red= #" & $CRLF & "Green= #" & $CRLF & "Blue=#", _ 
        mGetRed(rgbvalue), mgetGreen(rgbvalue), mGetBlue(rgbvalue))

    MSGBOX S
END FUNCTION

MCM

[Jonathan States]

Wow, thanks for all the feedback, guys!

This here pretty much clarifies things for me:

"What seems like wierd numbers (like "RGB(10,10,10)=657930 (very unexpected)") is a consequence of viewing as decimal. In this case:
657930 = 10 + (10 * 256) + (10 * 65536)"

And the methods you all outlined should come in handy, too!

Thank you very much.

[Mark Hunter]

Dale,

Thanks. PBs functions do use BGR. What I had in mind, and should have pointed out, was HTML, which uses RGB.

ADDED: Some API functions use the RGB format as well. PB has a function that converts between the two formats called BGR. From the help file: “The BGR function translates an RGB value to its BGR equivalent by swapping the first and third bytes and returning the result. ... calling BGR a second time converts a BGR value back to ... RGB format.” So it looks like BGR might better be called ColorSwap.