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How to replace a color in an HBITMAP

, 5 Feb 2012
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Replacing a color by another in transparent bitmaps.

Replace color screenshot

Introduction

When I wrote this function my problem was to replace one color by another on transparent bitmaps. My images were resources bitmaps, which I store in an ImageList for easy transparency.

There is no easy way to directly access a bitmap's pixel on Win32. If you're interested in doing that, this article may help you understand the usage of CreateDIBSection.

  • If you have to load a bitmap from a resource and make many color replacements, or if you have to change a color in a HBITMAP, this function is for you.
  • If you have a bitmap in a resource and want to replace one or more colors on load, it's better to use CreateMappedBitmap. You can find in the sample program a ReplaceColor function which uses CreateMappedBitmap.

I've made the same code using only BitBlt. BitBlt is really fast but the creation of the mask bitmap is so slow that the whole function is twice slower than the code using CreateDIBSection (sources are in the sample).

Limitations

My code always return a 32 bit bitmap. If you need to keep your original bitmap bit per pixels, you'll have two options:

  • You can rewrite it with GetDIBits. You will need special code for monochromes to 32 bit bitmaps.
  • You can BitBlt the 32 bit bitmap to your less color DC. It's easy, slow, and you will lose some colors in the process.

Sample program

The sample program you can download does the following:

  • Creates a window in WinMain.
  • Loads a bitmap from resources WM_NCCREATE.
  • Adds this bitmap to an ImageList WM_NCCREATE.
  • Uses ReplaceColor to get a copy of the bitmap with one color replaced by another (4 times) WM_NCCREATE.
  • Displays all the stored images in the window WM_PAINT.
  • Cleans everything WM_DESTROY.

Easy to use

A short sample of the usage of ReplaceColor:

HBITMAP hBmp2 = LoadBitmap(g_hinstance,MAKEINTRESOURCE(IDB_SAMPLEBITMAP));
HBITMAP hBmp = ReplaceColor(hBmp2,0xff0000,0x00ff00); // replace blue by green
DeleteObject(hBmp2);

// Use your modified Bitmap here 

DeleteObject(hBmp);

ReplaceColor source code

The ReplaceColor function is a pure Win32 function. It doesn't make any use of MFC. Its code is standalone, you can cut and paste it without modifications to your code.

#define COLORREF2RGB(Color) (Color & 0xff00) | ((Color >> 16) & 0xff) \
                                 | ((Color << 16) & 0xff0000)

//-------------------------------------------------------------------------------
// ReplaceColor
//
// Author    : Dimitri Rochette drochette@coldcat.fr
// Specials Thanks to Joe Woodbury for his comments and code corrections
//
// Includes  : Only <windows.h>

//
// hBmp         : Source Bitmap
// cOldColor : Color to replace in hBmp
// cNewColor : Color used for replacement
// hBmpDC    : DC of hBmp ( default NULL ) could be NULL if hBmp is not selected
//
// Retcode   : HBITMAP of the modified bitmap or NULL for errors
//
//-------------------------------------------------------------------------------
HBITMAP ReplaceColor(HBITMAP hBmp,COLORREF cOldColor,COLORREF cNewColor,HDC hBmpDC)
{
    HBITMAP RetBmp=NULL;
    if (hBmp)
    {
        HDC BufferDC=CreateCompatibleDC(NULL);    // DC for Source Bitmap
        if (BufferDC)
        {
            HBITMAP hTmpBitmap = (HBITMAP) NULL;
            if (hBmpDC)
                if (hBmp == (HBITMAP)GetCurrentObject(hBmpDC, OBJ_BITMAP))
            {
                hTmpBitmap = CreateBitmap(1, 1, 1, 1, NULL);
                SelectObject(hBmpDC, hTmpBitmap);
            }

            HGDIOBJ PreviousBufferObject=SelectObject(BufferDC,hBmp);
            // here BufferDC contains the bitmap
            
            HDC DirectDC=CreateCompatibleDC(NULL); // DC for working
            if (DirectDC)
            {
                // Get bitmap size
                BITMAP bm;
                GetObject(hBmp, sizeof(bm), &bm);

                // create a BITMAPINFO with minimal initilisation 
                // for the CreateDIBSection
                BITMAPINFO RGB32BitsBITMAPINFO; 
                ZeroMemory(&RGB32BitsBITMAPINFO,sizeof(BITMAPINFO));
                RGB32BitsBITMAPINFO.bmiHeader.biSize=sizeof(BITMAPINFOHEADER);
                RGB32BitsBITMAPINFO.bmiHeader.biWidth=bm.bmWidth;
                RGB32BitsBITMAPINFO.bmiHeader.biHeight=bm.bmHeight;
                RGB32BitsBITMAPINFO.bmiHeader.biPlanes=1;
                RGB32BitsBITMAPINFO.bmiHeader.biBitCount=32;

                // pointer used for direct Bitmap pixels access
                UINT * ptPixels;    

                HBITMAP DirectBitmap = CreateDIBSection(DirectDC, 
                                       (BITMAPINFO *)&RGB32BitsBITMAPINFO, 
                                       DIB_RGB_COLORS,
                                       (void **)&ptPixels, 
                                       NULL, 0);
                if (DirectBitmap)
                {
                    // here DirectBitmap!=NULL so ptPixels!=NULL no need to test
                    HGDIOBJ PreviousObject=SelectObject(DirectDC, DirectBitmap);
                    BitBlt(DirectDC,0,0,
                                   bm.bmWidth,bm.bmHeight,
                                   BufferDC,0,0,SRCCOPY);

                       // here the DirectDC contains the bitmap

                    // Convert COLORREF to RGB (Invert RED and BLUE)
                    cOldColor=COLORREF2RGB(cOldColor);
                    cNewColor=COLORREF2RGB(cNewColor);

                    // After all the inits we can do the job : Replace Color
                    for (int i=((bm.bmWidth*bm.bmHeight)-1);i>=0;i--)
                    {
                        if (ptPixels[i]==cOldColor) ptPixels[i]=cNewColor;
                    }
                    // little clean up
                    // Don't delete the result of SelectObject because it's 
                    // our modified bitmap (DirectBitmap)
                       SelectObject(DirectDC,PreviousObject);

                    // finish
                    RetBmp=DirectBitmap;
                }
                // clean up
                DeleteDC(DirectDC);
            }            
            if (hTmpBitmap)
            {
                SelectObject(hBmpDC, hBmp);
                DeleteObject(hTmpBitmap);
            }
            SelectObject(BufferDC,PreviousBufferObject);
            // BufferDC is now useless
            DeleteDC(BufferDC);
        }
    }
    return RetBmp;
}

License

This article, along with any associated source code and files, is licensed under A Public Domain dedication

About the Author

Dimitri Rochette
Software Developer (Senior)
France France
No Biography provided

Comments and Discussions

 
QuestionWhy not sent changed bmmp to clipboard? Pinmembersunwolf_00118-Oct-04 16:16 
GeneralLoading bitmap Pinmembervivadotnet23-Jun-04 8:23 
GeneralRe: Loading bitmap PinmemberDimitri Rochette23-Jun-04 10:30 
GeneralThanks for the code snipit PinmemberSAHorowitz19-Apr-04 4:03 
QuestionHow can i change a specific Pixel in a Bitmap to Transparent PinmemberAzhar Javaid21-Jul-03 1:21 
AnswerRe: How can i change a specific Pixel in a Bitmap to Transparent PinmemberDimitri Rochette21-Jul-03 13:02 
QuestionGetting hbitmap from imagelist ? Pinmemberselecta16-Jan-03 12:33 
AnswerRe: Getting hbitmap from imagelist ? PinmemberDimitri Rochette16-Jan-03 13:11 
You can create a Dc then draw your selected bitmap in then use this dc to have a bitmap.
But isnt it better to modify your bitmap directly in your imagelist ?
 
In the function Replacebitmap replace

for (int i=((bm.bmWidth*bm.bmHeight)-1);i>=0;i--)
{
if (ptPixels[i]==cOldColor) ptPixels[i]=cNewColor;
}

 
By

int xFrom=(single_image_width * image_to_modify_position);
int xTo=(single_image_width * (image_to_modify_position+1));
int posxy;
for (int j=0;j<bm.height;j++)
for (int i=xFrom;i<xTo;i++)
{
posxy=i+(j*bm.width);
if (ptPixels[posxy]==cOldColor) ptPixels[posxy]=cNewColor;
}

Easy to make some improvements like removing the j*bm.width from the second for.
Wrote that fast at night and havent tested it. i think that if there's a mistake you should find it fast.

GeneralRe: Getting hbitmap from imagelist ? Pinmemberselecta16-Jan-03 14:15 
GeneralPossible Alternative PinsussAnonymous27-Sep-02 4:47 
GeneralRe: Possible Alternative PinmemberWREY28-Sep-02 11:48 
GeneralPossible problems with the code PinmemberJoe Woodbury17-Sep-02 20:48 
GeneralRe: Possible problems with the code PinmemberDimitri Rochette20-Sep-02 14:48 
GeneralRe: Possible problems with the code PinmemberJoe Woodbury20-Sep-02 16:51 
GeneralRe: Possible problems with the code PinmemberDimitri Rochette21-Sep-02 7:22 
GeneralRe: Possible problems with the code PinmemberHarald Krause27-Sep-02 1:13 
GeneralRe: Possible problems with the code PinsussAnonymous17-Feb-03 16:34 
General. PinmemberGoran Mitrovic4-Sep-02 13:19 
GeneralRe: . PinmemberDimitri Rochette6-Sep-02 10:52 
GeneralRe: . PinmemberGoran Mitrovic6-Sep-02 14:27 
Generala stupid question... PinmemberPaolo Messina4-Sep-02 11:55 
GeneralRe: a stupid question... PinmemberChristian Graus4-Sep-02 12:03 
GeneralRe: a stupid question... PinmemberPaolo Messina4-Sep-02 13:25 

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