How to replace a color in an HBITMAP

Disclaimer

This code was written in 2002 for article on codeproject. I updated it in 2025 to compile in x64 with visual 2022 but no other change were made. There are multiple implementations in the files to answer questions I received at time on CodeProject.

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

				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;
}