cancelling colors in an image

[Penny]

how do I make everything non-black in an image become white (for example so every pixel that isn't black (which will be text) becomes the same color (white for example)?

[Bert]

I've never heard of someone asking to do such a thing. You have my attention. Would you elaborate on what you want to do? (The purpose of the function you need)

Edited October 30, 2009 by Volly

[Penny]

I want to clean an image that has "dirt" on it's background so it's easier to OCR the text on it. which is all black.

for example

becoming

(roughly)

Edited October 30, 2009 by Penny

[Bert]

Ah...that is a cool idea.

Give me a few minutes and let me see what I can come up with

[Bert]

what program are you using to edit the pic with? In looking at the help file, I'm not finding how to change the color of the pixel.

[Penny]

I'm trying to combine GDI+ and FreeImage.dll

[Malkey]

how do I make everything non-black in an image become white (for example so every pixel that isn't black (which will be text) becomes the same color (white for example)?

Here are two methods.

First one uses _GDIPlus_BitmapLockBits. And at about line #56, there is the regular expression pattern to match all colours that are not 0x000000FF, which in the 32 bit Hexidecimal colour format being used is fully opaque black.

This example was modified from the script from here.

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;
#include <ScreenCapture.au3>
#include <GDIPlus.au3>
; http://www.autoitscript.com/forum/index.php?showtopic=102626&view=findpost&p=729016
Global $sRegPath, $sImageIn, $sImageOut

$sImageIn = "C:\Program Files\AutoIt3\Examples\GUI\logo4.gif"
$sImageOut = @ScriptDir & "\B_W_Test.png"
Local $begin = TimerInit()

_ImageNonBlackToWhite(_ScreenCapture_Capture("", 0, 0, 200, 200, False), $sImageOut)
;OR
;_ImageNonBlackToWhite($sImageIn, $sImageOut)

ConsoleWrite("Time taken: " & Round(TimerDiff($begin), 2) & " milliseconds" & @CRLF)
If FileExists($sImageOut) Then ShellExecute($sImageOut)


Func _ImageNonBlackToWhite($sInFile, $sOutFile)
    Local $hImage, $iW, $iH, $tBitmapData, $iStride, $iScan0, $iX, $iY, $hBitmap1, $hBMP1

    _GDIPlus_Startup()
    If Number($sInFile) Then
        $hImage = _GDIPlus_BitmapCreateFromHBITMAP($sInFile)
        _WinAPI_DeleteObject($sInFile)
    Else
        $hImage = _GDIPlus_ImageLoadFromFile($sInFile)
    EndIf
    $iW = _GDIPlus_ImageGetWidth($hImage)
    $iH = _GDIPlus_ImageGetHeight($hImage)
    ;
    Local $aRet, $hBmp, $hBitmap, $hGraphic
    $aRet = _GDIPlus_ImageGetPixelFormat($hImage)
    $hBmp = _WinAPI_CreateBitmap($iW, $iH, 1, 32)
    $hBitmap = _GDIPlus_BitmapCreateFromHBITMAP($hBmp)
    _WinAPI_DeleteObject($hBmp)
    $hGraphic = _GDIPlus_ImageGetGraphicsContext($hBitmap)
    _GDIPlus_GraphicsDrawImage($hGraphic, $hImage, 0, 0)
    _GDIPlus_ImageDispose($hImage)
    _GDIPlus_GraphicsDispose($hGraphic)
    $hImage = _GDIPlus_BitmapCloneArea($hBitmap, 0, 0, $iW, $iH, $GDIP_PXF32ARGB)
    _GDIPlus_BitmapDispose($hBitmap)

    $tBitmapData = _GDIPlus_BitmapLockBits($hImage, 0, 0, $iW, $iH, $GDIP_ILMWRITE, $GDIP_PXF32ARGB)
    $iStride = DllStructGetData($tBitmapData, "stride")
    $iScan0 = DllStructGetData($tBitmapData, "Scan0")


    Local $v_BufferA = DllStructCreate("byte[" & $iH * $iW * 4 & "]", $iScan0) ; Create DLL structure for all pixels
    Local $AllPixels = DllStructGetData($v_BufferA, 1)
    Local $sREResult1 = StringRegExpReplace(StringTrimLeft($AllPixels, 2), "(.{8})", "\1 ")
    Local $sPix = "0x" & StringStripWS(StringRegExpReplace($sREResult1, _
            "(?i)([^0][0-9a-f]{7} )|([0-9a-f][^0][0-9a-f]{6} )|([0-9a-f]{2}[^0][0-9a-f]{5}FF )|([0-9a-f]{3}[^0][0-9a-f]{4} )|([0-9a-f]{4}[^0][0-9a-f]{3} )|([0-9a-f]{5}[^0][0-9a-f]{2} )|([0-9a-f]{6}[^f]{2} )", " FFFFFFFF "), 8)

    $AllPixels = DllStructSetData($v_BufferA, 1, $sPix)

    _GDIPlus_BitmapUnlockBits($hImage, $tBitmapData)
    _GDIPlus_ImageSaveToFile($hImage, $sOutFile)
    _GDIPlus_ImageDispose($hImage)
    _GDIPlus_Shutdown()
EndFunc ;==>_ImageNonBlackToWhite
;

The second example uses raster operation code in the _WinAPI_BitBlt function. This script is more of a proof of concept than a practical working example.

This script was modified from the script from here.

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#include <WinAPI.au3>
#include <ScreenCapture.au3>
#include <GDIPlus.au3>
#include <GUIConstants.au3>
#include <WindowsConstants.au3>
#include <misc.au3>

Global $iX = 0, $iY = 0, $iWidth = 600, $iHeight = 400, $iH, $iW
; Modified from http://www.autoitscript.com/forum/index.php?showtopic=77580&view=findpost&p=561542
Global $iTransparentColor = 0x000000 ;; = 0x3A6EA5 ;0xFFFFFF ;
;if Not IsNumber($iTransparentColor) Then $iTransparentColor = "0x" & Hex(PixelGetColor(3,3),6) ;GetPixel($hGUI2,3,3)
BitmapMasking(@ScriptDir & "\test.png", 0, 0, $iWidth, $iHeight)
;ShellExecute(@DesktopDir & "\test.png")

While GUIGetMsg() <> -3
    Sleep(10)
WEnd

Func BitmapMasking($sFileName = "", $iX=0, $iY=0 , $iWidth=10 , $iHeight=10 )
    Local $hWnd, $hDDC, $hCDC, $hBMP, $aIcon, $hIcon

    $iW = $iWidth
    $iH = $iHeight
    $hWnd = _WinAPI_GetDesktopWindow()
    $hDDC = _WinAPI_GetDC($hWnd)
    $hCDC = _WinAPI_CreateCompatibleDC($hDDC)
    $hBMP = _WinAPI_CreateCompatibleBitmap($hDDC, $iW, $iH)
    _WinAPI_SelectObject($hCDC, $hBMP)

    ; Create GUI for Color Mask
    $GUICompDir = GUICreate("Color Mask", $iWidth, $iHeight, 0, 0)
    WinSetTrans("Color Mask", "", 255)
    GUISetBkColor($iTransparentColor, $GUICompDir) ;<=== TransparentColor ==
    GUISetState()
    $hDDC1 = _WinAPI_GetDC($GUICompDir)
    $hCDC1 = _WinAPI_CreateCompatibleDC($hDDC1)
    $hBMP1 = _WinAPI_CreateCompatibleBitmap($hDDC1, $iW, $iH)
    _WinAPI_SelectObject($hCDC1, $hBMP1)

    ; Create GUI for B/W Mask
    $hGUI = GUICreate("B/W Mask", $iWidth, $iHeight, -1, @DesktopHeight / 2)
    ;WinSetTrans("B/W Mask", "", 254)
    GUISetState()
    $hDDC2 = _WinAPI_GetDC($hGUI)
    $hCDC2 = _WinAPI_CreateCompatibleDC($hDDC2)
    $hBMP2 = _WinAPI_CreateCompatibleBitmap($hDDC2, $iW, $iH)
    _WinAPI_SelectObject($hCDC2, $hBMP2)

    ; Create GUI
    $hGUIRes = GUICreate("Result", $iWidth, $iHeight, @DesktopWidth / 2, 10)
    GUISetState()
    $hDDC3 = _WinAPI_GetDC($hGUIRes)
    $hCDC3 = _WinAPI_CreateCompatibleDC($hDDC3)
    $hBMP3 = _WinAPI_CreateCompatibleBitmap($hDDC3, $iW, $iH)
    _WinAPI_SelectObject($hCDC3, $hBMP3)

    ; A one bit per pixel bitmap
    $hBitmapMask = _WinAPI_CreateBitmap($iW, $iH, 1, 1, 0)
    $hdcMem = _WinAPI_CreateCompatibleDC(0);
    _WinAPI_SelectObject($hdcMem, $hBitmapMask);
    ;MsgBox(0,"","")

    ; The GUI associated with $hDDC1 has the background color set black,
    ; and, $hDDC is the handle of the display device context for the captured desktop area.
    _WinAPI_BitBlt($hDDC1, 0, 0, $iW, $iH, $hDDC, $iX, $iY, $SRCCOPY)   ; Direct copy
    ;MsgBox(0,"","")

    _WinAPI_BitBlt($hdcMem, 0, 0, $iW, $iH, $hDDC1, $iX, $iY, $SRCCOPY) ; Direct copy

    ; Color mask - Has black where black will be
    _WinAPI_BitBlt($hDDC1, 0, 0, $iW, $iH, $hdcMem, $iX, $iY, $SRCINVERT) ;XOR operator

    ; Black/White Mask - Has white where the black will be, all other colors appear black.
    _WinAPI_BitBlt($hDDC2, 0, 0, $iW, $iH, $hdcMem, $iX, $iY, $SRCINVERT) ; XOR operator
    ;MsgBox(0,"","")

    _WinAPI_BitBlt($hDDC2, 0, 0, $iW, $iH, $hDDC1, $iX, $iY, $PATINVERT) ; XOR operator
    ;MsgBox(0,"","")

    ; Invert mask window and copy to Result window
    _WinAPI_BitBlt($hDDC3, 0, 0, $iW, $iH, $hDDC2, $iX, $iY, $SRCINVERT) ; XOR operator


    ; Copy Dislpay DC ($hDDC3) to memory DC ($hCDC3) also known as $hBMP3
    _WinAPI_BitBlt($hCDC3, 0, 0, $iW, $iH, $hDDC3, $iX, $iY, $SRCCOPY)  ; Direct copy

    _WinAPI_ReleaseDC($hWnd, $hDDC)
    _WinAPI_DeleteDC($hCDC)
    _WinAPI_ReleaseDC($GUICompDir, $hDDC1)
    _WinAPI_DeleteDC($hCDC1)
    _WinAPI_ReleaseDC($hGUI, $hDDC2)
    _WinAPI_DeleteDC($hCDC2)
    _WinAPI_ReleaseDC($hGUIRes, $hDDC3)
    _WinAPI_DeleteDC($hCDC3)
    _WinAPI_DeleteObject($hBMP)
    _WinAPI_DeleteObject($hBMP1)
    _WinAPI_DeleteObject($hBMP2)
    _WinAPI_DeleteObject($hBitmapMask)

    If $sFileName = "" Then Return $hBMP3
    _ScreenCapture_SaveImage($sFileName, $hBMP3)
    _WinAPI_DeleteObject($hBMP3)

    ;If FileExists($sFileName) Then ShellExecute($sFileName)

EndFunc ;==>BitmapMasking