RGB565的转换

24bit RGB888 -> 16bit RGB565 的转换

24ibt RGB888 {R7 R6 R5 R4 R3 R2 R1 R0} {G7 G6 G5 G4 G3 G2 G1 G0} {B7 B6 B5 B4 B3 B2 B1 B0}

16bit RGB656 {R7 R6 R5 R4 R3} {G7 G6 G5 G4 G3 G2} {B7 B6 B5 B4 B3}

可以修正，比如（当然人眼无法感觉，但是RG888-RGB565-RGB888的时候更好补偿）

R：197=>197>>3=24

R：197=192+5=>24+0.625≈25

所以

R5=R[2] ? R[7:3]+1 : R[7:3];

G5=G[1] ? G[7:2]+1 : G[7:2];

B5=B[2] ? B[7:3]+1 : B[7:3];

16bit RGB565 -> 24bit RGB888 的转换

16bit RGB656 {R4 R3 R2 R1 R0} {G5 G4 G3 G2 G1 G0} {B4 B3 B2 B1 B0}

24ibt RGB888 {R4 R3 R2 R1 R0 0 0 0} {G5 G4 G3 G2 G1 G0 0 0} {B4 B3 B2 B1 B0 0 0 0}

    进行精度补偿（剩余的用低位进行补偿）

24ibt RGB888 {R4 R3 R2 R1 R0 R2 R1 R0} {G5 G4 G3 G2 G1 G0 G1 G0} {B4 B3 B2 B1 B0 B2 B1 B0}

 

 

总结一下：

1、量化压缩的方法：

   三个字节对应取高位

 

2、量化补偿的方法：

 （1） 将原数据填充至高位

 （2） 对于低位，用原始数据的低位进行补偿

 

3、RGB565互转代码

 

#define RGB565_MASK_RED        0xF800   
#define RGB565_MASK_GREEN    0x07E0   
#define RGB565_MASK_BLUE       0x001F   

void rgb565_2_rgb24(BYTE *rgb24, WORD rgb565)    //分离出单独的RGB
{    
 
      rgb24[2] = (rgb565 & RGB565_MASK_RED) >> 11;      

      rgb24[1] = (rgb565 & RGB565_MASK_GREEN) >> 5;   
      
      rgb24[0] = (rgb565 & RGB565_MASK_BLUE);   

      //往高位移动填满单字节的8位
      rgb24[2] <<= 3;   
      rgb24[1] <<= 2;   
      rgb24[0] <<= 3;   
}

 

 

　　

 

 

下面的代码来自这个网址：

http://bbs.csdn.net/topics/350153377

 

#ifndef WIDTHBYTES
#define WIDTHBYTES(bits) ((DWORD)(((bits)+31) & (~31)) / 8)
#endif
// BITMAPINFOHEADER m_bmih;
// BYTE *m_pR;
// BYTE *m_pG;
// BYTE *m_pB;
BOOL CImageProcessor::LoadFileFromBitmap(LPCTSTR lpFileName)
{
    if(lpFileName == NULL)
    {
        return FALSE;
    }
 
    HANDLE hFile = ::CreateFile(lpFileName, GENERIC_READ, FILE_SHARE_READ | FILE_SHARE_WRITE, NULL, OPEN_EXISTING, 0, NULL);
    if(hFile == INVALID_HANDLE_VALUE)
    {
        return FALSE;
    }
 
    BOOL bRet = FALSE;
 
    do
    {
        LARGE_INTEGER liSize;
        liSize.QuadPart = 0;
        ::GetFileSizeEx(hFile, &liSize);
 
        BITMAPFILEHEADER bmfh;
        BITMAPINFOHEADER bmih;
 
        DWORD dwByteRead = 0;
        ::ReadFile(hFile, &bmfh, sizeof(bmfh), &dwByteRead, NULL);
        if(dwByteRead < sizeof(bmfh))
        {
            break;
        }
 
        if(bmfh.bfType != ‘MB‘ || bmfh.bfSize > liSize.QuadPart || bmfh.bfOffBits > liSize.QuadPart)
        {
            break;
        }
 
        dwByteRead = 0;
        ::ReadFile(hFile, &bmih, sizeof(bmih), &dwByteRead, NULL);
        if(dwByteRead < sizeof(bmih))
        {
            break;
        }
 
        int nBitmapSize = abs(bmih.biHeight) * WIDTHBYTES(bmih.biWidth * bmih.biBitCount);
        if(bmih.biPlanes != 1)
        {
            break;
        }
        if(bmih.biBitCount != 1 && bmih.biBitCount != 4 && bmih.biBitCount != 8 && bmih.biBitCount != 16 && bmih.biBitCount != 24 && bmih.biBitCount != 32)
        {
            break;
        }
        if(bmih.biCompression != BI_RGB && bmih.biCompression != BI_BITFIELDS)
        {
            break;
        }
        if(bmih.biWidth <= 0 || bmih.biHeight == 0)
        {
            break;
        }
        if(bmfh.bfOffBits + nBitmapSize > liSize.QuadPart)
        {
            break;
        }
 
        m_pR = new BYTE[bmih.biWidth * abs(bmih.biHeight)];
        m_pG = new BYTE[bmih.biWidth * abs(bmih.biHeight)];
        m_pB = new BYTE[bmih.biWidth * abs(bmih.biHeight)];
 
        if(bmih.biBitCount < 16)
        {
            //...
        }
        else if(bmih.biBitCount == 16)
        {
            //...
        }
        else if(bmih.biBitCount == 24)
        {
            ::SetFilePointer(hFile, bmfh.bfOffBits, NULL, SEEK_SET);
 
            BYTE *pData = new BYTE[nBitmapSize];
 
            dwByteRead = 0;
            ::ReadFile(hFile, pData, nBitmapSize, &dwByteRead, NULL);
 
            BYTE *pR = m_pR;
            BYTE *pG = m_pG;
            BYTE *pB = m_pB;
 
            for(int j = 0; j < abs(bmih.biHeight); j++)
            {
                BYTE *pTemp = pData + WIDTHBYTES(bmih.biWidth * bmih.biBitCount) * j;
                for(int i = 0; i < bmih.biWidth; i++)
                {
                    *pB++ = *pTemp++;
                    *pG++ = *pTemp++;
                    *pR++ = *pTemp++;
                }
            }
 
            delete[] pData;
        }
        else if(bmih.biBitCount == 32)
        {
            //...
        }
 
        memcpy(&m_bmih, &bmih, sizeof(m_bmih));
 
        bRet = TRUE;
    }
    while(0);
 
    CloseHandle(hFile);
 
    return bRet;
}
 
BOOL CImageProcessor::SaveFile565(HANDLE hFile)
{
    BITMAPFILEHEADER bmfh;
    BITMAPINFOHEADER bmih;
    memset(&bmfh, 0, sizeof(bmfh));
    memset(&bmih, 0, sizeof(bmih));
 
    int nBitmapSize = abs(m_bmih.biHeight) * WIDTHBYTES(m_bmih.biWidth * 16);
 
    bmfh.bfType = ‘MB‘;
    bmfh.bfOffBits = sizeof(bmfh) + sizeof(bmih) + 12;
    bmfh.bfSize = bmfh.bfOffBits + nBitmapSize;
 
    bmih.biSize = sizeof(bmih);
    bmih.biWidth = m_bmih.biWidth;
    bmih.biHeight = m_bmih.biHeight;
    bmih.biPlanes = 1;
    bmih.biBitCount = 16;
    bmih.biCompression = BI_BITFIELDS;
    bmih.biSizeImage = nBitmapSize;
 
    BYTE *pData = new BYTE[nBitmapSize];
    memset(pData, 0, nBitmapSize);
 
    BYTE *pR = m_pR;
    BYTE *pG = m_pG;
    BYTE *pB = m_pB;
 
    for(int j = 0; j < abs(bmih.biHeight); j++)
    {
        WORD *pTemp = (WORD *)(pData + WIDTHBYTES(bmih.biWidth * 16) * j);
 
        for(int i = 0; i < bmih.biWidth; i++)
        {
#if 1
            *pTemp++ = ((WORD)(*pR++ << 8) & 0xf800) | ((WORD)(*pG++ << 3) & 0x07e0) | ((WORD)(*pB++ >> 3) & 0x001f);
#else
            int nR = (*pR++ + 4) >> 3;
            int nG = (*pG++ + 2) >> 2;
            int nB = (*pB++ + 4) >> 3;
            if(nR > 31) nR = 31;
            if(nG > 63) nG = 63;
            if(nB > 31) nB = 31;
            *pTemp++ = (nR << 11) | (nG << 5) | nB;
#endif
        }
    }
 
    DWORD nRGBMask[3];
    nRGBMask[0] = 0xf800;
    nRGBMask[1] = 0x07e0;
    nRGBMask[2] = 0x001f;
 
    DWORD dwByteWritten = 0;
    ::WriteFile(hFile, &bmfh, sizeof(bmfh), &dwByteWritten, NULL);
    ::WriteFile(hFile, &bmih, sizeof(bmih), &dwByteWritten, NULL);
    ::WriteFile(hFile, nRGBMask, sizeof(nRGBMask), &dwByteWritten, NULL);
    ::WriteFile(hFile, pData, nBitmapSize, &dwByteWritten, NULL);
 
    delete[] pData;
 
    return TRUE;
}