我這里有這段代碼，它截取螢屏截圖和位圖并將其保存為 BMP 檔案。它作業得很好，但我希望能夠修改這些位并使其成為灰度而不是 RGB 貼圖。
我找到了一種方法來做到這一點，但我必須保存 BMPINFOHEADER 和 RGBQUAD 陣列，然后用它作業的灰度函式讀取它，但大小保持不變。
我對此很菜鳥，但我認為灰度影像應該比 RGB 影像小很多。
有沒有一種方法可以立即從位圖中洗掉顏色，而無需重新讀取和修改它？
int CaptureBMP(LPCTSTR szFile)
{
// Source[1]
HDC hdcScr, hdcMem;
HBITMAP hbmScr;
BITMAP bmp;
int iXRes, iYRes;
// Create a normal DC and a memory DC for the entire screen. The
// normal DC provides a "snapshot" of the screen contents. The
// memory DC keeps a copy of this "snapshot" in the associated
// bitmap.
hdcScr = CreateDC("DISPLAY", NULL, NULL, NULL);
hdcMem = CreateCompatibleDC(hdcScr);
iXRes = GetDeviceCaps(hdcScr, HORZRES);
iYRes = GetDeviceCaps(hdcScr, VERTRES);
// Create a compatible bitmap for hdcScreen.
hbmScr = CreateCompatibleBitmap(hdcScr, iXRes, iYRes);
if (hbmScr == 0) return 0;
// Select the bitmaps into the compatible DC.
if (!SelectObject(hdcMem, hbmScr)) return 0;
// Copy color data for the entire display into a
// bitmap that is selected into a compatible DC.
if (!StretchBlt(hdcMem,0, 0, iXRes, iYRes,hdcScr,0, 0, iXRes, iYRes,SRCCOPY)) return 0;
// Source[2]
PBITMAPINFO pbmi;
WORD cClrBits;
// Retrieve the bitmap's color format, width, and height.
if (!GetObject(hbmScr, sizeof(BITMAP), (LPSTR)&bmp)) return 0;
// Convert the color format to a count of bits.
cClrBits = (WORD)(bmp.bmPlanes * bmp.bmBitsPixel);
if (cClrBits == 1)
cClrBits = 1;
else if (cClrBits <= 4)
cClrBits = 4;
else if (cClrBits <= 8)
cClrBits = 8;
else if (cClrBits <= 16)
cClrBits = 16;
else if (cClrBits <= 24)
cClrBits = 24;
else cClrBits = 32;
// Allocate memory for the BITMAPINFO structure. (This structure
// contains a BITMAPINFOHEADER structure and an array of RGBQUAD
// data structures.)
if (cClrBits != 24)
pbmi = (PBITMAPINFO)LocalAlloc(LPTR, sizeof(BITMAPINFOHEADER) sizeof(RGBQUAD) * (1 << cClrBits));
// There is no RGBQUAD array for the 24-bit-per-pixel format.
else
pbmi = (PBITMAPINFO)LocalAlloc(LPTR,sizeof(BITMAPINFOHEADER));
// Initialize the fields in the BITMAPINFO structure.
pbmi->bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
pbmi->bmiHeader.biWidth = bmp.bmWidth;
pbmi->bmiHeader.biHeight = bmp.bmHeight;
pbmi->bmiHeader.biPlanes = bmp.bmPlanes;
pbmi->bmiHeader.biBitCount = bmp.bmBitsPixel;
if (cClrBits < 24)
pbmi->bmiHeader.biClrUsed = (1 << cClrBits);
// If the bitmap is not compressed, set the BI_RGB flag.
pbmi->bmiHeader.biCompression = BI_RGB;
// Compute the number of bytes in the array of color
// indices and store the result in biSizeImage.
pbmi->bmiHeader.biSizeImage = (pbmi->bmiHeader.biWidth 7) / 8 * pbmi->bmiHeader.biHeight * cClrBits;
// Set biClrImportant to 0, indicating that all of the
// device colors are important.
pbmi->bmiHeader.biClrImportant = 0;
HANDLE hf; // file handle
BITMAPFILEHEADER hdr; // bitmap file-header
PBITMAPINFOHEADER pbih; // bitmap info-header
LPBYTE lpBits; // memory pointer
DWORD dwTotal; // total count of bytes
DWORD cb; // incremental count of bytes
BYTE* hp; // byte pointer
DWORD dwTmp;
pbih = (PBITMAPINFOHEADER)pbmi;
lpBits = (LPBYTE)GlobalAlloc(GMEM_FIXED, pbih->biSizeImage);
if (!lpBits) return 0;
// Retrieve the color table (RGBQUAD array) and the bits
// (array of palette indices) from the DIB.
if (!GetDIBits(hdcMem, hbmScr, 0, (WORD)pbih->biHeight, lpBits, pbmi, DIB_RGB_COLORS)) return 0;
// Create the .BMP file.
hf = CreateFile(szFile, GENERIC_READ | GENERIC_WRITE, (DWORD)0, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, (HANDLE)NULL);
if (hf == INVALID_HANDLE_VALUE) return 0;
hdr.bfType = 0x4d42; // 0x42 = "B" 0x4d = "M"
// Compute the size of the entire file.
hdr.bfSize = (DWORD)(sizeof(BITMAPFILEHEADER) pbih->biSize pbih->biClrUsed * sizeof(RGBQUAD) pbih->biSizeImage);
hdr.bfReserved1 = 0;
hdr.bfReserved2 = 0;
// Compute the offset to the array of color indices.
hdr.bfOffBits = (DWORD)sizeof(BITMAPFILEHEADER)
pbih->biSize pbih->biClrUsed *
sizeof(RGBQUAD);
// Copy the BITMAPFILEHEADER into the .BMP file.
if (!WriteFile(hf, (LPVOID)&hdr, sizeof(BITMAPFILEHEADER), (LPDWORD)&dwTmp, NULL)) return 0;
// Copy the BITMAPINFOHEADER and RGBQUAD array into the file.
if (!WriteFile(hf, (LPVOID)pbih, sizeof(BITMAPINFOHEADER)
pbih->biClrUsed * sizeof(RGBQUAD),
(LPDWORD)&dwTmp, NULL))
return 0;
// Copy the array of color indices into the .BMP file.
dwTotal = cb = pbih->biSizeImage;
hp = lpBits;
if (!WriteFile(hf, (LPSTR)hp, (int)cb, (LPDWORD)&dwTmp, NULL)) return 0;
// Close the .BMP file.
if (!CloseHandle(hf)) return 0;
// Free memory.
GlobalFree((HGLOBAL)lpBits);
ReleaseDC(0, hdcScr);
ReleaseDC(0, hdcMem);
return 1;
}
uj5u.com熱心網友回復：
我使用了陣列轉換，主要是從原始真彩色圖的rgbRed、rgbGreen和rgbBlue分量到灰度影像的灰度值Y。
可以使用以下公式獲得：
Y=0.299 * rgbRed 0.587 * rgbGreen 0.114 * rgbBlue
處理代碼已經添加到你的代碼中，可以參考下面的代碼，輸出檔案大小是原來的1/4。
#pragma pack(1)
typedef struct tag_color_32 {
BYTE Red;
BYTE Green;
BYTE Blue;
BYTE Alpha;
}color_32;
int CaptureBMP(LPCTSTR szFile)
{
// Source[1]
HDC hdcScr, hdcMem;
HBITMAP hbmScr;
BITMAP bmp;
.................
.................
// Copy the array of color indices into the .BMP file.
dwTotal = cb = pbih->biSizeImage;
hp = lpBits;
if (!WriteFile(hf, (LPSTR)hp, (int)cb, (LPDWORD)& dwTmp, NULL)) return 0;
// Close the .BMP file.
if (!CloseHandle(hf)) return 0;
/*********************edit 2022/1/7******************************/
FILE* originImg;
fopen_s(&originImg, "lena-32.bmp", "rb");
if (originImg == NULL) return 0;
int sizeFileHeader = sizeof(BITMAPFILEHEADER);
int sizeInfoHeader = sizeof(BITMAPINFOHEADER);
BITMAPFILEHEADER* bitmapFileHeader = new BITMAPFILEHEADER[sizeFileHeader 1];
BITMAPINFOHEADER* bitmapInfoHeader = new BITMAPINFOHEADER[sizeInfoHeader 1];
memset(bitmapFileHeader, 0, sizeFileHeader 1);
memset(bitmapInfoHeader, 0, sizeInfoHeader 1);
fread(bitmapFileHeader, sizeof(char), sizeFileHeader, originImg);
fseek(originImg, sizeFileHeader, 0);
fread(bitmapInfoHeader, sizeof(char), sizeInfoHeader, originImg);
int srcImageLineByteCount = (((bitmapInfoHeader->biWidth * 32) 31) / 32) * 4; //Calculates the number of bytes of pixels per line of the original 32 bitmap
int grayImageLineByteCount = (((bitmapInfoHeader->biWidth) * 8 31) / 32) * 4; //Calculate the number of bytes of pixels in each row of 8-bit grayscale map
//************Bitmap header**********************
//Creates a two-dimensional array with high biHeight and width srcImageLineByteCount, and initializes the array
color_32* origImgData = new color_32[bitmapInfoHeader->biHeight * bitmapInfoHeader->biWidth];
for (int i = 0; i < bitmapInfoHeader->biHeight * bitmapInfoHeader->biWidth; i )
{
fread(origImgData i, 4, 1, originImg);
}
fclose(originImg);
// palette
RGBQUAD* pRgbQuards = new RGBQUAD[256];
for (int i = 0; i < 256; i )
{
pRgbQuards[i].rgbBlue = i;
pRgbQuards[i].rgbRed = i;
pRgbQuards[i].rgbGreen = i;
pRgbQuards[i].rgbReserved = 0;
}
//Modify headers
bitmapInfoHeader->biBitCount = 8;
bitmapInfoHeader->biClrUsed = 256;
bitmapInfoHeader->biSizeImage = (bitmapInfoHeader->biHeight) * grayImageLineByteCount;
//8 is a grayscale image with 256 RGBQUAD data structures. A color palette takes up 4 bytes of data, so the color palette length of 256 color images is 256*4 and 1024 bytes
bitmapFileHeader->bfOffBits = sizeof(BITMAPFILEHEADER) sizeof(BITMAPINFOHEADER) sizeof(RGBQUAD) * 256; //The offset plus the size of the palette
bitmapFileHeader->bfSize = bitmapFileHeader->bfOffBits bitmapInfoHeader->biSizeImage;
//Write the data
FILE* grayImg;
fopen_s(&grayImg, "lena-gray.bmp", "wb");
//Written to the file
fwrite(bitmapFileHeader, sizeof(char), sizeof(BITMAPFILEHEADER), grayImg);
fwrite(bitmapInfoHeader, sizeof(char), sizeof(BITMAPINFOHEADER), grayImg);
fwrite(pRgbQuards, sizeof(RGBQUAD), 256, grayImg);
//Grayscale map a two-dimensional array of bitmap data
for (int i = 0; i < bitmapInfoHeader->biHeight; i )
{
for (int j = 0; j < bitmapInfoHeader->biWidth; j ) //The number of bytes of pixels per row of a grayscale image
{
float pr = origImgData[i * bitmapInfoHeader->biWidth j].Red;
float pg = origImgData[i * bitmapInfoHeader->biWidth j].Green;
float pb = origImgData[i * bitmapInfoHeader->biWidth j].Blue;
BYTE data = pr * 0.299 pg * 0.587 pb * 0.114;
fwrite(&data, 1, 1, grayImg);
for (int j = bitmapInfoHeader->biWidth; j < grayImageLineByteCount; j ) {
BYTE data = 0;
fwrite(&data, 1, 1, grayImg);
}
}
}
fclose(grayImg);
//Free memory.
delete[]origImgData;
/*******************edit 2022/1/7****************************/
// Free memory.
GlobalFree((HGLOBAL)lpBits);
ReleaseDC(0, hdcScr);
ReleaseDC(0, hdcMem);
return 1;
}
int main()
{
CaptureBMP(L"lena-32");
std::cout << "Hello World!\n";
}
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