Grey Scale

[Grincheux]

Hello,

Can anyone give me the formula to transfrom color images to grey image ?

Thanks :(

[Siekmanski]

29.9 %  red
58,7 %  green
11.4 %  blue

= 100% grey

[MichaelW]

The formula that I have, from Programmer's Guide to the EGA and VGA Cards by Richard F. Ferraro, is:

Gray Scale = (.30 * red) + (.59 * green) + (.11 * blue)

I have seen some variations, but I think this is the one that was developed originally by IBM, and implemented in the VGA BIOS for the SumToGrayScale function.

The grays displayed by this test app don't look right to me, but the numbers seem to check out.

Code Select Expand


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    include \masm32\include\masm32rt.inc

    Paint_Proc PROTO :DWORD,:DWORD

    FRGB MACRO red, green, blue
        xor eax, eax
        mov ah, blue    ; blue
        mov al, green   ; green
        rol eax, 8
        mov al, red     ; red
        EXITM <eax>
    ENDM   

    GRAY MACRO red, green, blue
        LOCAL rval
        .data
          rval dd 0
          align 4
        .code
        fld8  <red>.0
        fld8  0.30
        fmul
        fld8  <green>.0
        fld8  0.59
        fmul
        fld8  <blue>.0
        fld8  0.11
        fmul
        fadd
        fadd
        fistp rval
        mov   eax, rval
        rol   eax, 8
        or    eax, rval
        rol   eax, 8
        or    eax, rval
        EXITM <eax>
    ENDM
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    .data
        hInst     dd          0
        hWnd      dd          0
        wc        WNDCLASSEX  <>
        msg       MSG         <>
        className db          "gray_scale_test"
    .code
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start:
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    MsgBox 0,uhex$(GRAY(255,0,0)),"R",0
    MsgBox 0,uhex$(GRAY(0,255,0)),"G",0
    MsgBox 0,uhex$(GRAY(0,0,255)),"B",0

    mov   hInst, rv(GetModuleHandle, NULL)
    mov   wc.cbSize,        sizeof WNDCLASSEX
    mov   wc.style,         CS_HREDRAW or CS_VREDRAW \
                              or CS_BYTEALIGNWINDOW
    mov   wc.lpfnWndProc,   OFFSET WndProc
    mov   wc.cbClsExtra,    NULL
    mov   wc.cbWndExtra,    NULL
    m2m   wc.hInstance,     hInst
    mov   wc.hbrBackground, COLOR_BTNFACE+1
    mov   wc.lpszMenuName,  NULL
    mov   wc.lpszClassName, OFFSET className
    mov   wc.hIcon,         NULL
    mov   wc.hCursor,       NULL
    mov   wc.hIconSm,       0
    invoke RegisterClassEx, ADDR wc
    invoke CreateWindowEx,  WS_EX_OVERLAPPEDWINDOW,
                            ADDR className,
                            chr$("Test"),
                            WS_OVERLAPPEDWINDOW,
                            0,0,600,400,
                            NULL, NULL,
                            hInst, NULL
    mov   hWnd, eax
    invoke ShowWindow, hWnd, SW_SHOWNORMAL
    invoke UpdateWindow, hWnd
  msgLoop:
    invoke GetMessage, ADDR msg, NULL, 0, 0
    .IF (eax != 0)
        invoke TranslateMessage, ADDR msg
        invoke DispatchMessage, ADDR msg
        jmp   msgLoop
    .ENDIF
    exit msg.wParam
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WndProc proc hWin:DWORD, uMsg:DWORD, wParam:DWORD, lParam:DWORD
    LOCAL hDC :DWORD
    LOCAL ps  :PAINTSTRUCT
   
    .IF (uMsg == WM_DESTROY)
        invoke PostQuitMessage, NULL
        return 0
    .ELSEIF (uMsg == WM_PAINT)
        invoke BeginPaint, hWin, ADDR ps
        mov hDC, eax
        invoke Paint_Proc, hWin, hDC
        invoke EndPaint, hWin, ADDR ps
        return 0
    .ENDIF
    invoke DefWindowProc, hWin, uMsg, wParam, lParam
    ret
WndProc endp
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Paint_Proc proc hWin:DWORD, hDC:DWORD

    invoke GetStockObject, DC_PEN
    invoke SelectObject, hDC, eax
    invoke GetStockObject, DC_BRUSH
    invoke SelectObject, hDC, eax

    invoke SetDCPenColor, hDC, FRGB(255,0,0)
    invoke SetDCBrushColor, hDC, FRGB(255,0,0)
    invoke Rectangle, hDC, 20, 20, 120, 120

    invoke SetDCPenColor, hDC, GRAY(255,0,0)
    invoke SetDCBrushColor, hDC, GRAY(255,0,0)
    invoke Rectangle, hDC, 130, 20, 230, 120

    invoke SetDCPenColor, hDC, FRGB(0,255,0)
    invoke SetDCBrushColor, hDC, FRGB(0,255,0)
    invoke Rectangle,hDC, 20, 130, 120, 230

    invoke SetDCPenColor, hDC, GRAY(0,255,0)
    invoke SetDCBrushColor, hDC, GRAY(0,255,0)
    invoke Rectangle, hDC, 130, 130, 230, 230

    invoke SetDCPenColor, hDC, FRGB(0,0,255)
    invoke SetDCBrushColor, hDC, FRGB(0,0,255)
    invoke Rectangle,hDC, 20, 240, 120, 340

    invoke SetDCPenColor, hDC, GRAY(0,0,255)
    invoke SetDCBrushColor, hDC, GRAY(0,0,255)
    invoke Rectangle, hDC, 130, 240, 230, 340

    ret
Paint_Proc endp
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end start


[Grincheux]

Thank You !

This is really what I need.

Here is what I have done with it :

      mov   DWord Ptr [_dCent],100
      fild   DWord Ptr [_dCent]
      fst   QWord Ptr [_dCent]

      fild   DWord Ptr [dwGrey_Red]
      fdiv   QWord Ptr [_dCent]
      fst   QWord Ptr [_dRed]

      fild   DWord Ptr [dwGrey_Green]
      fdiv   QWord Ptr [_dCent]
      fst   QWord Ptr [_dGreen]

      fild   DWord Ptr [dwGrey_Blue]
      fdiv   QWord Ptr [_dCent]
      fst      QWord Ptr [_dBlue]

      mov   ebx,DWord Ptr [lpImageBits]
      mov   edx,DWord Ptr [lpWork]
      mov   edi,DWord Ptr [Image.bmHeight]

GreyScale_Work_Loop :

      mov   esi,DWord Ptr [Image.bmWidth]

GreyScale_Work_Loop_1 :

      mov   eax,DWord Ptr [ebx]
      and   eax,0ffh
      mov   DWord Ptr [_dwBlue],eax

      mov   eax,DWord Ptr [ebx]
      shr   eax,8
      and   eax,0ffh
      mov   DWord Ptr [_dwGreen],eax

      mov   eax,DWord Ptr [ebx]
      shr   eax,16
      mov   DWord Ptr [_dwRed],eax

      fild   DWord Ptr [_dwRed]
      fld   QWord Ptr [_dRed]
      fmul
      fld   DWord Ptr [_dwGreen]
      fild   DWord Ptr [_dGreen]
      fmul
      fld   DWord Ptr [_dwBlue]
      fild   DWord Ptr [_dBlue]
      fmul
      fadd
      fadd
      fistp   DWord Ptr [_dVal]

      mov   eax,DWord Ptr [_dVal]
      rol   eax,8
      or   eax,DWord Ptr [_dVal]
      rol   eax,8
      or   eax,DWord Ptr [_dVal]

      mov   DWord Ptr [edx],eax

GreyScale_Work_Loop_2 :

      add   ebx,SIZEOF DWord
      add   edx,SIZEOF DWord

I have found that good values also are Red=70%, Green=70% and Blue=5%.

In this case the sum of Red, Green and Blue is greather than 100% ! But this not not an error. Images are lighter than with the previous formula. If you want to limit the sum to 100%, you have to do :

factor = 1 / (Red+Green+blue)

and apply this factor to each color.


If you have others ideas or formulas for grayscale and image working send them to me.

[MichaelW]

The attachment is supposed to be a visual test to determine if the grayscale results for the coefficients 0.30, 0.59, and 0.11 reasonably mimic the luminosity for the corresponding primary color. The general idea here is to create primary and grayscale gradients that fade to black at the same rate. If the gradients have the same luminosity, then the primary and corresponding grayscale gradients should fade into the black background at about the same horizontal position. For my display (a Sony Trinitron), the red and green grayscales are OK, but the blue grayscale seems generally darker than the blue primary, and the grayscale gradient fades into the black background a little (perhaps 40 pixels) before the blue gradient does. The coefficients 0.29, 0.53, and 0.18 seem to work OK.





[attachment deleted by admin]

[Grincheux]

The values you give do darks images. The lighter values are 70,70 and 10. I tooke them from "The Gimp". "Photoshop" has the possibility to desaturate, this give grey image leaving white areas unchanged and black areas become grey. I don't know how it does. But this the best result... this "Photoshop" too.

Where can I find formulas about effets to give an image ?

I have found some effects in assembly language, they all are written by BitRAKE and seems good. I have not tested them again.

I would like to convert part of a color image into grey part, and others effects without using the last parameter of "StretchBlt". In my program I have the original image bits into a buffer, this buffer is modified by effects and then put on the window. The image size on the window is different that the original. When the program save a result it saves a memory buffer not the window image.

Thank you for every one who helps me.

[MichaelW]

The problems I see with 70-70-10 are that the luminosity would increase, and the conversion would not differentiate between reds and greens.

http://www.gimp.org/tutorials/Color2BW/

[Grincheux]

I used the same doc...

[DC]

for r, g, b
(r*ctl(0)+g*ctl(1)+b*ctl(2))/(ctl(0)+ctl(1)+ctl(2))
ctl() range 1 to ? (0 to 255 in the example FF plugin: Grey.8bf - dividing by 0 works in Filter Factory for some reason)

this file is a plugin for Photoshop or PSP or ...
www.bmath.net/dc/download/ind/DC_GreyScaler4.8bf

[MichaelW]

Desaturate in GIMP:

Note on the first page for the Grayscale function: "The formula used in the GIMP is Y = 0.3R + 0.59G + 0.11B; this result is known as luminance".

http://gimp-savvy.com/BOOK/node54.html

http://www.informit.com/articles/article.asp?p=131019&seqNum=4&rl=1

[P1]

Donkey has some Graphics Code/Library, including a fast grayscales routine here:
http://donkey.visualassembler.com/

I know a lot of his code is in GoAsm.  So some conversion maybe needed.

Regards,  P1  :8)

[PBrennick]

I took a look at Donkey's code and it is interesting to note that he is using essentually the same values as Michael.

   25 => 11.36% Blue
129 => 58.63% Green
   66 => 30.00% Red
---------------------------------
220 => 99.99% Gray

Take it for what it is worth...
Paul

[Grincheux]

Thanks to everyone :boohoo:,

Now I have a lot to do.

All these informations will me in my "Images Effects" programs.