Help : RGB -> Black and White

[Jashugan357]

Hi,
I'm looking for a simple code to put an Image (Colored one) into Black and White...

Any links or sample codes ?

[Zaei]

The easiest way to do it is to simply extract the individual RGB values from the color, average them, and create a new color using the average for all three components. Simple, but it is incorrect, visually, as far as I know. Someone else may be in here at some point to give you a better solution.

Z.

[Sastraxi]

Do this:

Function GetLum(R As Long, G As Long, B As Long) As Long
Dim Hi As Long
Dim Lo As Long
 
    Hi = Max(R, G, B)
    Lo = Min(R, G, B)   
    GetLum = (Hi + Lo) / 2
 
End Function
Function Min(R As Long, G As Long, B As Long) As Long
    If R < G Then
        If R < B Then
            Min = R
        Else
            Min = B
        End If
    Else
        If G < B Then
            Min = G
        Else
            Min = B
        End If
    End If
End Function
Function Max(R As Long, G As Long, B As Long) As Long
    If R > G Then
        If R > B Then
            Max = R
        Else
            Max = B
        End If
    Else
        If G > B Then
            Max = G
        Else
            Max = B
        End If
    End If
End Function

[Jashugan357]

Here is what i have done, i think it's more smart...

[jim mcnamara]

In the graphics biz, the standard way is to calculate the luminance value for each point and then map it over to an array of
RGB(0,0,0) -> RGB(255,255,255).

I've posted this code about four-five times now - do a search on
this forum for the word 'luminance' Don't search on my name - my account got hosed and the search engine thinks my old posts belong to 'Guest' or something.

[CornedBee]

It's a weighted average. Using the weighting factors
R: 0.3333 (1/3)
G: 0.59
B: 011

So the grey value would be
(0.3333 * R + 0.59 * G + 0.11 * B) / 3

[cyborg]

try mine:

Public Sub BlackAndWhite(ByVal picPictureBox As PictureBox)
Dim X As Single
Dim Y As Single
Dim PrevColor As Long
Dim NewColor As Long
Dim TempColor As Single
 
For Y = 0 To picPictureBox.ScaleHeight - 1
    For X = 0 To picPictureBox.ScaleWidth - 1
        PrevColor = GetPixel(picPictureBox.hdc, X, Y)
        TempColor = Round2((GetRed(PrevColor) + GetGreen(PrevColor) + GetBlue(PrevColor)) / 3)
        NewColor = RGB(TempColor, TempColor, TempColor)
        SetPixelV picPictureBox.hdc, X, Y, NewColor
    Next X
Next Y
 
End Sub
 
Public Function GetRed(Color As Long) As Integer
GetRed = Color And 255
End Function
 
Public Function GetGreen(Color As Long) As Integer
GetGreen = (Color And 65280) \ 256
End Function
 
Public Function GetBlue(Color As Long) As Integer
GetBlue = (Color And 16711680) \ 65535
End Function
 
Public Function Round2(Number As Single) As Integer
If Number - Round(Number) >= 0.05 Then Number = Round(Number, 1) + 0.1
If Number - Round(Number) < 0.05 Then Number = Round(Number, 1)
Round2 = Number
End Function

[cyborg]

here's a sample image changed with my code:

[Zaei]

Originally posted by cyborg
try mine:

Public Sub BlackAndWhite(ByVal picPictureBox As PictureBox)
Dim X As Single
Dim Y As Single
Dim PrevColor As Long
Dim NewColor As Long
Dim TempColor As Single
 
For Y = 0 To picPictureBox.ScaleHeight - 1
    For X = 0 To picPictureBox.ScaleWidth - 1
        PrevColor = GetPixel(picPictureBox.hdc, X, Y)
        TempColor = Round2((GetRed(PrevColor) + GetGreen(PrevColor) + GetBlue(PrevColor)) / 3)
        NewColor = RGB(TempColor, TempColor, TempColor)
        SetPixelV picPictureBox.hdc, X, Y, NewColor
    Next X
Next Y
 
End Sub
 
Public Function GetRed(Color As Long) As Integer
GetRed = Color And 255
End Function
 
Public Function GetGreen(Color As Long) As Integer
GetGreen = (Color And 65280) \ 256
End Function
 
Public Function GetBlue(Color As Long) As Integer
GetBlue = (Color And 16711680) \ 65535
End Function
 
Public Function Round2(Number As Single) As Integer
If Number - Round(Number) >= 0.05 Then Number = Round(Number, 1) + 0.1
If Number - Round(Number) < 0.05 Then Number = Round(Number, 1)
Round2 = Number
End Function

Perhaps this was the first post?

Z.

[cyborg]

you mean your post?
i just showed a routine i made to make it easy for him...
the other 2 ones didnt work properly...
the first one took the average from the lowest and highest value from r, g and b.....
the other one changed to less colors...

[Jashugan357]

Just look closely at the name of the function : Black & White, it means NO GREY. (2 Colors : 1. White, 2. Black )

I've build this little Module on the principles that :
(Recall)

RGB(0,0,0) = BLACK

RGB(255,255,255) = WHITE

So a colour is coded on 3 Bytes stored in a long (4 Bytes)
R G B R G B
a Colour is coded to &H 00 00 00 to & H FF FF FF

I extract each colors (R, G, B) by an AND and see if each of them are bigger than 127 (Brithness indeed, no ?)


Your code is great, and helpfull, thanks !


But what do you think about writing a function like :

GreyImage(pPictureBox as PictureBox, byval GreyLevel as byte)

Where GreyLevel is the accuracy in grey :
Example :
(Grey level cannot be 0 or 1), because
GreyLevel =2, it will be black and white only
GreyLevel =3 will be black and white and Perfect Grey

and so on... with different grey levels

[Jashugan357]

Once the picture is modified, if i want to save to disk, it doesn't work using the SavePicture function

Should i call a API function and give it hDC of the picture box ??

[CornedBee]

For the GrayLevel function:
pseudocode

Dim px As Pixel
Dim clr As Color
Dim gr As Byte
Dim i As Integer
If GrayLevel < 2 Then
  Exit Sub
End If
For px = Each Pixel in pPictureBox
  clr = px.color
  gr = (0.3333*clr.red+0.59*clr.green+0.11*clr.blue)/3
  ' You need to refine this part, it doesn't work this way
  For i = 1 To GrayLevel-1
    If gr < (255 / GrayLevel)*i Then
      gr = (255/GrayLevel)*i-1
      Goto Done
    End If
  Next i
  gr = 255
Done:
  clr.red = clr.green = clr.blue = gr
  px.color = clr
Next px

The problem of this spacing algorithm is that every one that I could come up when thinking about this would either not work with more than 2 greys or exactly black & white.

[Jashugan357]

Thanks
But, I haven't understand your post on :

It's a weighted average. Using the weighting factors
R: 0.3333 (1/3)
G: 0.59
B: 011

So the grey value would be
(0.3333 * R + 0.59 * G + 0.11 * B) / 3

Can you develop why is there coefficient in front of R,G,B
I thought grey was RGB(127,127,127) .....
Thanks.

[CornedBee]

There are many shades of gray, computers usually display 256 (RGB(0,0,0) to RGB(255,255,255)).
When you have a color picture you usually take the average of the color components to get the shade of grey this particular color correspondends to. But it would be wrong to simply use every color component the same (0.3333*r+0.3333*g+0.3333*b), because the human eye values the components differently. A bright green looks far brighter than a bright blue. Therefore you have to use a weighted average: (0.3333*r+0.59*g+0.11*b). I have to correct myself, there is no /3 there.

[Jashugan357]

I didn't know that, is there any article on the subject ?

[CornedBee]

There probably is, but I don't know where...

Try googling for "grayscale conversion" or similar terms.

[Sastraxi]

If you want a black-and-white artistic feeling, use one of the excellent grayscale code snippets in this thread, and if R, G, and B are under 128, make all 0 (black). If they're 128 or over, make them 255 (white).

If you want something more accurate, you'll have to look into things like dithering and error defusion.