Question

我正在拍摄一个窗口的屏幕截图，以便使用Leptonica进行处理，然后使用Tesseract进行一些OCR

问题是，性能方面我希望避免将BMP写入和读取光盘而只是在内存中工作。这是我制作屏幕截图的方式：

int width, height = 0;

HDC hdcWindow;
HDC hdcMemDC = NULL;
HBITMAP hbmScreen = NULL;
BITMAP bmpScreen;

// Retrieve the handle to a display device context for the client 
// area of the window. 
//hdcScreen = GetDC(NULL);
//hdcWindow = GetDC(hWnd);

hdcWindow = GetDC(hWnd);

// Create a compatible DC which is used in a BitBlt from the window DC
hdcMemDC = CreateCompatibleDC(hdcWindow);

if (!hdcMemDC)
{
    MessageBox(hWnd, L"CreateCompatibleDC has failed", L"Failed", MB_OK);
    goto done;
}

// Get the client area for size calculation
RECT rcClient;
GetClientRect(hWnd, &rcClient);


// Create a compatible bitmap from the Window DC
hbmScreen = CreateCompatibleBitmap(hdcWindow, rcClient.right - rcClient.left, rcClient.bottom - rcClient.top);

if (!hbmScreen)
{
    MessageBox(hWnd, L"CreateCompatibleBitmap Failed", L"Failed", MB_OK);
    goto done;
}

// Select the compatible bitmap into the compatible memory DC.
SelectObject(hdcMemDC, hbmScreen);

// Bit block transfer into our compatible memory DC.
if (!BitBlt(hdcMemDC,
    0, 0,
    rcClient.right - rcClient.left, rcClient.bottom - rcClient.top,
    hdcWindow,
    0, 0,
    SRCCOPY))
{
    MessageBox(hWnd, L"BitBlt has failed", L"Failed", MB_OK);
    goto done;
}

// Get the BITMAP from the HBITMAP
GetObject(hbmScreen, sizeof(BITMAP), &bmpScreen);

BITMAPFILEHEADER   bmfHeader;
BITMAPINFOHEADER   bi;

bi.biSize = sizeof(BITMAPINFOHEADER);
bi.biWidth = bmpScreen.bmWidth;
bi.biHeight = bmpScreen.bmHeight;
bi.biPlanes = 1;
bi.biBitCount = 32;
bi.biCompression = BI_RGB;
bi.biSizeImage = 0;
bi.biXPelsPerMeter = 0;
bi.biYPelsPerMeter = 0;
bi.biClrUsed = 0;
bi.biClrImportant = 0;

DWORD dwBmpSize = ((bmpScreen.bmWidth * bi.biBitCount + 31) / 32) * 4 * bmpScreen.bmHeight;

// Starting with 32-bit Windows, GlobalAlloc and LocalAlloc are implemented as wrapper functions that 
// call HeapAlloc using a handle to the process's default heap. Therefore, GlobalAlloc and LocalAlloc 
// have greater overhead than HeapAlloc.
HANDLE hDIB = GlobalAlloc(GHND, dwBmpSize);
char *lpbitmap = (char *)GlobalLock(hDIB);

// Gets the "bits" from the bitmap and copies them into a buffer 
// which is pointed to by lpbitmap.
GetDIBits(hdcWindow, hbmScreen, 0,
    (UINT)bmpScreen.bmHeight,
    lpbitmap,
    (BITMAPINFO *)&bi, DIB_RGB_COLORS);

// A file is created, this is where we will save the screen capture.
HANDLE hFile = CreateFile(L"pics/UI.bmp",
    GENERIC_WRITE,
    0,
    NULL,
    CREATE_ALWAYS,
    FILE_ATTRIBUTE_NORMAL, NULL);

// Add the size of the headers to the size of the bitmap to get the total file size
DWORD dwSizeofDIB = dwBmpSize + sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);

//Offset to where the actual bitmap bits start.
bmfHeader.bfOffBits = (DWORD)sizeof(BITMAPFILEHEADER) + (DWORD)sizeof(BITMAPINFOHEADER);

//Size of the file
bmfHeader.bfSize = dwSizeofDIB;

//bfType must always be BM for Bitmaps
bmfHeader.bfType = 0x4D42; //BM   

DWORD dwBytesWritten = 0;
WriteFile(hFile, (LPSTR)&bmfHeader, sizeof(BITMAPFILEHEADER), &dwBytesWritten, NULL);
WriteFile(hFile, (LPSTR)&bi, sizeof(BITMAPINFOHEADER), &dwBytesWritten, NULL);
WriteFile(hFile, (LPSTR)lpbitmap, dwBmpSize, &dwBytesWritten, NULL);

//Unlock and Free the DIB from the heap
GlobalUnlock(hDIB);
GlobalFree(hDIB);

//Close the handle for the file that was created
CloseHandle(hFile);

width = rcClient.right - rcClient.left;
height = rcClient.bottom - rcClient.top;

//Clean up
done:
DeleteObject(hbmScreen);
DeleteObject(hdcMemDC);
ReleaseDC(hWnd, hdcWindow);

这就是我读它的方式：

PIX* pixUI = pixRead("pics/UI.bmp");

所以，我已经看到该库有PIX * pixReadMemBmp ( const l_uint8 *cdata, size_t size ) method，其中l_uint8是unsigned char缓冲区

问题是，我不明白如何从我的HBITMAP或BITMAP对象中获取这样的缓冲区。

Answer 1

首先将位图复制到缓冲区，然后将此缓冲区移交给<html> <head> <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.3.0/jquery.min.js"></script> <script type="text/javascript"> $(function() { $(".word").keyup(function() { var word=$(this).val(); $(".word_preview").html(word); return false; }); }); </script> <script> function myFunction() { var str = document.getElementById("demo").innerHTML; var res = str.replace(/[^]0/g, '<span style="color:black">').replace(/[^]1/g, '<span style="color:red">').replace(/[^]2/g, '<span style="color:green">').replace(/[^]3/g, '<span style="color:yellow">').replace(/[^]4/g, '<span style="color:blue">').replace(/[^]5/g, '<span style="color:cyan">').replace(/[^]6/g, '<span style="color:#D02090">').replace(/[^]7/g, '<span style="color:white">'); document.getElementById("demo").innerHTML = res; }; </script> </head> <body> Enter name: <br/> <input type="text" name="maprotation" size="50" id="textfield" class="word" class="Stil69"> <input type="reset" name="Submit3" value="Reset" /> <br/><br/> <h3>2. Click the button to preview your colored name.</h3> <br/> <input type="button" onclick="myFunction()" value="Click here"/> <br/><br/> <table bgcolor="#333333"><tr><td><span class="word_preview" id="demo"><td></span></tr></table> <br/> </body> </html>。必须完成复制，因为我认为，pixReadMemBmp()函数需要位图数据前面的两个位图标题，就像它在文件中一样。伪代码：

pixReadMemBmp()

将Windows BITMAP转换为PIX（unsigned char缓冲区）

1 个答案: