我可以将 bmp 内存数据转换为更小的 png 内存数据吗？

Question

我的程序的目的是每 1/16 秒进行一次屏幕捕获，并通过套接字将其发送到远程服务器。

目前这个程序可以使用BMP格式的屏幕截图，但是，BMP格式的数据发送的字节太多，发送和接收过程明显变慢。

我的想法是：如果我能把BMP转换成PNG，然后在发送前压缩，也许程序运行起来会更流畅。

这是我的代码，select 来自 gh0st 项目

LPVOID  m_lpvFullBits = NULL;
HDC m_hFullDC, m_hFullMemDC;
LPBITMAPINFO  m_lpbmi_full;
m_hFullDC = GetDC(NULL);
int m_nFullWidth    = ::GetSystemMetrics(SM_CXSCREEN);
int m_nFullHeight   = ::GetSystemMetrics(SM_CYSCREEN);
m_hFullMemDC    = ::CreateCompatibleDC(m_hFullDC);

m_lpbmi_full = (BITMAPINFO *) new BYTE[40];
BITMAPINFOHEADER    *lpbmih = &(m_lpbmi_full ->bmiHeader);
lpbmih->biSize = sizeof(BITMAPINFOHEADER);
lpbmih->biWidth = m_nFullWidth  ;
lpbmih->biHeight = m_nFullHeight    ;
lpbmih->biPlanes = 1;
lpbmih->biBitCount = 32;       // 32 bit per pixel
lpbmih->biCompression = BI_RGB;
lpbmih->biXPelsPerMeter = 0;
lpbmih->biYPelsPerMeter = 0;
lpbmih->biClrUsed = 0;
lpbmih->biClrImportant = 0;
lpbmih->biSizeImage = (((lpbmih->biWidth * lpbmih->biBitCount + 31) & ~31) >> 3) * lpbmih->biHeight;

HBITMAP m_hFullBitmap   = ::CreateDIBSection(m_hFullDC, m_lpbmi_full, DIB_RGB_COLORS, &m_lpvFullBits, NULL, NULL);

::SelectObject(m_hFullMemDC, m_hFullBitmap);

::BitBlt(m_hFullMemDC, 0, 0, m_nFullWidth, m_nFullHeight, m_hFullDC, 0, 0, SRCCOPY);

直到这条语句：

::BitBlt(m_hFullMemDC, 0, 0, m_nFullWidth, m_nFullHeight, m_hFullDC, 0, 0, SRCCOPY);

BMP像素数据保存在m_lpvFullBits开始的地址，对吧？

现在我想知道的是，我可以使用当前已知的宽度，高度，BMP 像素数据..，重建一个新的 png 格式的内存数据，它比当前的 BMP 数据小得多，并通过套接字将新的 png 格式数据发送到远程服务器？

感谢您的帮助

Answer 1

是的，你可以。在我看来，GDI+ 足以胜任这项任务。首先，从 HBITMAP 创建一个 Gdiplus::Bitmap，然后将其保存到 IStream。从 IStream 您可以通过 IStream::Stat() 获得字节数。最后用IStream::Read()读入字节数组。现在您的 PNG 已保存在内存中。

这是一个最小示例，您可以将其复制并粘贴到 CPP 文件并进行编译。请注意，省略了错误处理和清理代码。

#include <Windows.h>
#include <gdiplus.h>
#include <iostream>
using namespace Gdiplus;

#pragma comment(lib, "gdiplus.lib") // or you specify it in linker option

IStream * PngMemStreamFrom(HBITMAP hbm)
{
    // image/png  : {557cf406-1a04-11d3-9a73-0000f81ef32e}
    const CLSID clsidPngEncoder =
        { 0x557cf406, 0x1a04, 0x11d3,
        { 0x9a,0x73,0x00,0x00,0xf8,0x1e,0xf3,0x2e } };
    IStream *stream = NULL;
    Bitmap *bmp = Bitmap::FromHBITMAP(hbm, NULL);
    CreateStreamOnHGlobal(NULL, TRUE, &stream);
    bmp->Save(stream, &clsidPngEncoder);    
    delete bmp;
    return stream;
}

void ScreenshotTest(LPCWSTR szPath)
{
    LPVOID  m_lpvFullBits = NULL;
    HDC m_hFullDC, m_hFullMemDC;
    LPBITMAPINFO  m_lpbmi_full;
    m_hFullDC = GetDC(NULL);
    int m_nFullWidth    = ::GetSystemMetrics(SM_CXSCREEN);
    int m_nFullHeight   = ::GetSystemMetrics(SM_CYSCREEN);
    m_hFullMemDC    = ::CreateCompatibleDC(m_hFullDC);

    m_lpbmi_full = (BITMAPINFO *) new BYTE[40];
    BITMAPINFOHEADER    *lpbmih = &(m_lpbmi_full ->bmiHeader);
    lpbmih->biSize = sizeof(BITMAPINFOHEADER);
    lpbmih->biWidth = m_nFullWidth  ;
    lpbmih->biHeight = m_nFullHeight    ;
    lpbmih->biPlanes = 1;
    lpbmih->biBitCount = 32;       // 32 bit per pixel
    lpbmih->biCompression = BI_RGB;
    lpbmih->biXPelsPerMeter = 0;
    lpbmih->biYPelsPerMeter = 0;
    lpbmih->biClrUsed = 0;
    lpbmih->biClrImportant = 0;
    lpbmih->biSizeImage = (((lpbmih->biWidth * lpbmih->biBitCount + 31) & ~31) >> 3) * lpbmih->biHeight;

    HBITMAP m_hFullBitmap = ::CreateDIBSection(m_hFullDC, m_lpbmi_full, DIB_RGB_COLORS, &m_lpvFullBits, NULL, NULL);
    ::SelectObject(m_hFullMemDC, m_hFullBitmap);
    ::BitBlt(m_hFullMemDC, 0, 0, m_nFullWidth, m_nFullHeight, m_hFullDC, 0, 0, SRCCOPY);

    IStream *stream = PngMemStreamFrom(m_hFullBitmap);

    STATSTG stat = {0};
    stream->Stat(&stat, STATFLAG_NONAME);
    UINT64 cbSize = stat.cbSize.QuadPart;
    std::cout << "mem stream byte count = " << cbSize << "\n";
    LPBYTE buffer = new BYTE[cbSize];
    // IMPORTANT! must seek to offset zero before read it
    LARGE_INTEGER offZero = {0};
    stream->Seek(offZero, STREAM_SEEK_SET, NULL);
    stream->Read(buffer, cbSize, NULL);
    // do something with buffer, such as save to disk
    HANDLE hfile = CreateFile(szPath, GENERIC_WRITE, 0, NULL,
        CREATE_ALWAYS, 0, NULL);
    DWORD cbWritten = 0;
    WriteFile(hfile, buffer, cbSize, &cbWritten, NULL);
    CloseHandle(hfile);
    // TODO: release m_hFullDC, m_hFullMemDC... here
}

int main()
{
    ULONG_PTR token = NULL;
    GdiplusStartupInput gdipIn;
    GdiplusStartupOutput gdipOut;
    GdiplusStartup(&token, &gdipIn, &gdipOut);
    ScreenshotTest(L"D:\Test.png");
    GdiplusShutdown(token);
    return 0;
}

我可以将 bmp 内存数据转换为更小的 png 内存数据吗？

can I convert bmp in-memory data into a much more smaller png in-momory data?

winapi

png

bitblt