RGB色彩模式也就是“红绿蓝”模式是一种颜色标准,是通过对红(R)、绿(G)、蓝(B)三种颜色通道的变化以及它们相互之间的叠加来得到各式各样的颜色的,RGB即是代表红、绿、蓝三个通道的颜色,这个标准几乎囊括了人类视力所能感知的所有颜色,是目前运用最广的颜色系统之一。
1、RGB565格式说明
RGB565彩色模式, 一个像素占两个字节, 其中:第一个字节的前5位用来表示R(Red),第一个字节的后三位+第二个字节的前三位用来表示G(Green),第二个字节的后5位用来表示B(Blue)。如:15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
而bitmap图片是一个RGB888,每个像素由3个字节24位组成,R->8bit,G->8bit,B->8bit;RGB565 的每个pixels是由2字节组成,R->5bit,G->6bit,B->5bit。转换的思路是取出原图的点,对每个采样进行运算。
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; }