怎么样把RGB映射到256色上

Question

现在有一调色板有256项，每项为r,g,b三值，共占768,现24位RGB色使用该调色板，查找颜色最相近的调色板项代替原来颜色
编程实现 int fastFind(char *pal,r,g,b)
屏幕显示800*600*24

Answer 1

有个权值，
temp=(int)((float)(pData24[i*nLineBytes+3*j]*BLUE_WEIGHT+
(float)pData24[i*nLineBytes+3*j+1]*GREEN_WEIGHT+
(float)pData24[i*nLineBytes+3*j+2]*RED_WEIGHT));
其中，
#ifndef RED_WEIGHT
#define RED_WEIGHT 0.299
#endif
#ifndef GREEN_WEIGHT
#define GREEN_WEIGHT 0.587
#endif
#ifndef BLUE_WEIGHT
#define BLUE_WEIGHT 0.114
#endif

Answer 2

void OnConvertRGBto256()
{
LPBITMAPINFO lpBi;
LPBITMAPINFO lpBi24;
HGLOBAL hDIB;
DWORD dwSize;
int nSizeCT;
int i, j;
int n;
LPSTR lpRowSrc;
LPSTR lpRowTgt;
POSITION pos;
CGDIView *ptrView;
CPtrArray arRgbQuad;
LPRGBQUAD lpRgbQuad;
RGBQUAD rgbQuad;
BOOL bHit;
BOOL bStandardPal;
BYTE red, green, blue;
AfxGetApp()->DoWaitCursor(TRUE);
lpBi24=(LPBITMAPINFO)::GlobalLock(m_hDIB);
ASSERT(lpBi24);
for(j=0; j<lpBi24->bmiHeader.biHeight; j++)
{
lpRowSrc=
((LPSTR)lpBi24+
sizeof(BITMAPINFOHEADER)+
WIDTHBYTES(lpBi24->bmiHeader.biBitCount*lpBi24->bmiHeader.biWidth)*j
);
for(i=0; i<lpBi24->bmiHeader.biWidth; i++)
{
rgbQuad.rgbBlue=*lpRowSrc;
rgbQuad.rgbGreen=*(lpRowSrc+1);
rgbQuad.rgbRed=*(lpRowSrc+2);
rgbQuad.rgbReserved=0;
bHit=FALSE;
for(n=0; n<arRgbQuad.GetSize(); n++)
{
if
(
!memcmp
(
(LPSTR)&rgbQuad,
(LPSTR)arRgbQuad[n],
sizeof(RGBQUAD)
)
)
{
bHit=TRUE;
break;
}
}
if(bHit == FALSE)
{
lpRgbQuad=new RGBQUAD;
*lpRgbQuad=rgbQuad;
arRgbQuad.Add(lpRgbQuad);
}
lpRowSrc+=3;
}
}
if(arRgbQuad.GetSize() > 256)
{
while(arRgbQuad.GetSize())
{
delete (LPRGBQUAD)arRgbQuad.GetAt(0);
arRgbQuad.RemoveAt(0);
}
red=green=blue=0;
for(i=0; i<256; i++)
{
lpRgbQuad=new RGBQUAD;
lpRgbQuad->rgbBlue=blue;
lpRgbQuad->rgbGreen=green;
lpRgbQuad->rgbRed=red;
lpRgbQuad->rgbReserved=0;
if(!(red+=32))if(!(green+=32))blue+=64;
arRgbQuad.Add(lpRgbQuad);
}
bStandardPal=TRUE;
}
else bStandardPal=FALSE;
nSizeCT=256;
dwSize=
(
sizeof(BITMAPINFOHEADER)+
nSizeCT*sizeof(RGBQUAD)+
WIDTHBYTES(8*lpBi24->bmiHeader.biWidth)*lpBi24->bmiHeader.biHeight
);
hDIB=::GlobalAlloc(GHND, dwSize);
ASSERT(hDIB);
lpBi=(LPBITMAPINFO)::GlobalLock(hDIB);
ASSERT(lpBi);
*lpBi=*lpBi24;
lpBi->bmiHeader.biBitCount=8;
lpBi->bmiHeader.biSizeImage=WIDTHBYTES
(
8*lpBi->bmiHeader.biWidth
)*lpBi->bmiHeader.biHeight;
lpBi->bmiHeader.biClrUsed=0;
for(n=0; n<arRgbQuad.GetSize(); n++)
{
lpBi->bmiColors[n]=*(LPRGBQUAD)arRgbQuad[n];
}
for(j=0; j<lpBi->bmiHeader.biHeight; j++)
{
lpRowTgt=
(
(LPSTR)lpBi+
sizeof(BITMAPINFOHEADER)+
nSizeCT*sizeof(RGBQUAD)+
WIDTHBYTES(lpBi->bmiHeader.biBitCount*lpBi->bmiHeader.biWidth)*j
);
lpRowSrc=
(
(LPSTR)lpBi24+
sizeof(BITMAPINFOHEADER)+
WIDTHBYTES(lpBi24->bmiHeader.biBitCount*lpBi24->bmiHeader.biWidth)*j
);
for(i=0; i<lpBi->bmiHeader.biWidth; i++)
{
rgbQuad.rgbBlue=*lpRowSrc;
rgbQuad.rgbGreen=*(lpRowSrc+1);
rgbQuad.rgbRed=*(lpRowSrc+2);
rgbQuad.rgbReserved=0;
if(bStandardPal == TRUE)
{
if(rgbQuad.rgbBlue <= 0xdf)rgbQuad.rgbBlue+=0x20;
if(rgbQuad.rgbGreen <= 0xef)rgbQuad.rgbGreen+=0x10;
if(rgbQuad.rgbRed <= 0xef)rgbQuad.rgbRed+=0x10;
*lpRowTgt=(BYTE)
(
(0x00c0&rgbQuad.rgbBlue) |
((0x00e0&rgbQuad.rgbGreen)>>2) |
((0x00e0&rgbQuad.rgbRed)>>5)
);
}
else
{
for(n=0; n<arRgbQuad.GetSize(); n++)
{
if
(
!memcmp
(
(LPSTR)&rgbQuad,
(LPSTR)arRgbQuad[n],
sizeof(RGBQUAD)
)
)break;
}
*lpRowTgt=(BYTE)n;
}
lpRowSrc+=3;
lpRowTgt++;
}
}
::GlobalUnlock(m_hDIB);
::GlobalFree(m_hDIB);
::GlobalUnlock(hDIB);
m_hDIB=hDIB;
m_nBmpFormat=BMP_FORMAT_256COLOR;
while(arRgbQuad.GetSize())
{
delete (LPRGBQUAD)arRgbQuad.GetAt(0);
arRgbQuad.RemoveAt(0);
}
pos=GetFirstViewPosition();
ptrView=(CGDIView *)GetNextView(pos);
ASSERT(ptrView->IsKindOf(RUNTIME_CLASS(CGDIView)));
ptrView->LoadBitmap(m_hDIB);
AfxGetApp()->DoWaitCursor(FALSE);
}