屏幕截图和位图的复制部分在结构上有什么区别？

Question

我尝试使用问题的一个答案中的代码，当我运行在 "paint" 中打开一个位图文件后，选择了它的一部分，然后复制了它，程序会根据需要保存复制的图像，但是当我按 PrntScrn 时（屏幕截图出现在剪贴板中并在程序中标识为位图文件）程序将其保存为位图文件但是当我尝试打开它时我得到图像格式不受支持的消息。我猜这是因为我保存图像的方式。我的问题是两种类型的图像之间有什么区别，其中一种可以正常工作而另一种不能正常工作？

这是我的代码：

#include <iostream>
#include <fstream>
#include <windows.h>

typedef struct
{
    std::uint32_t biSize;
    std::int32_t  biWidth;
    std::int32_t  biHeight;
    std::uint16_t  biPlanes;
    std::uint16_t  biBitCount;
    std::uint32_t biCompression;
    std::uint32_t biSizeImage;
    std::int32_t  biXPelsPerMeter;
    std::int32_t  biYPelsPerMeter;
    std::uint32_t biClrUsed;
    std::uint32_t biClrImportant;
} DIB;

typedef struct
{
    std::uint16_t type;
    std::uint32_t bfSize;
    std::uint32_t reserved;
    std::uint32_t offset;
} HEADER;

typedef struct
{
    HEADER header;
    DIB dib;
} BMP;


int main()
{
    std::cout << "Format Bitmap: " << IsClipboardFormatAvailable(CF_BITMAP) << "\n";
    std::cout << "Format DIB: " << IsClipboardFormatAvailable(CF_DIB) << "\n";
    std::cout << "Format DIBv5: " << IsClipboardFormatAvailable(CF_DIBV5) << "\n";

    if (IsClipboardFormatAvailable(CF_BITMAP) || IsClipboardFormatAvailable(CF_DIB) || IsClipboardFormatAvailable(CF_DIBV5))
    {
        if (OpenClipboard(NULL))
        {
            HANDLE hClipboard = GetClipboardData(CF_DIB);

            if (!hClipboard)
            {
                hClipboard = GetClipboardData(CF_DIBV5);
            }

            if (hClipboard != NULL && hClipboard != INVALID_HANDLE_VALUE)
            {
                void* dib = GlobalLock(hClipboard);

                if (dib)
                {
                    DIB* info = reinterpret_cast<DIB*>(dib);
                    BMP bmp = { 0 };
                    bmp.header.type = 0x4D42;
                    bmp.header.offset = 54;
                    bmp.header.bfSize = info->biSizeImage + bmp.header.offset;
                    bmp.dib = *info;

                    std::cout << "Type: " << std::hex << bmp.header.type << std::dec << "\n";
                    std::cout << "bfSize: " << bmp.header.bfSize << "\n";
                    std::cout << "Reserved: " << bmp.header.reserved << "\n";
                    std::cout << "Offset: " << bmp.header.offset << "\n";
                    std::cout << "biSize: " << bmp.dib.biSize << "\n";
                    std::cout << "Width: " << bmp.dib.biWidth << "\n";
                    std::cout << "Height: " << bmp.dib.biHeight << "\n";
                    std::cout << "Planes: " << bmp.dib.biPlanes << "\n";
                    std::cout << "Bits: " << bmp.dib.biBitCount << "\n";
                    std::cout << "Compression: " << bmp.dib.biCompression << "\n";
                    std::cout << "Size: " << bmp.dib.biSizeImage << "\n";
                    std::cout << "X-res: " << bmp.dib.biXPelsPerMeter << "\n";
                    std::cout << "Y-res: " << bmp.dib.biYPelsPerMeter << "\n";
                    std::cout << "ClrUsed: " << bmp.dib.biClrUsed << "\n";
                    std::cout << "ClrImportant: " << bmp.dib.biClrImportant << "\n";

                    std::ofstream file("Test2.bmp", std::ios::out | std::ios::binary);
                    if (file)
                    {
                        file.write(reinterpret_cast<char*>(&bmp.header.type), sizeof(bmp.header.type));
                        file.write(reinterpret_cast<char*>(&bmp.header.bfSize), sizeof(bmp.header.bfSize));
                        file.write(reinterpret_cast<char*>(&bmp.header.reserved), sizeof(bmp.header.reserved));
                        file.write(reinterpret_cast<char*>(&bmp.header.offset), sizeof(bmp.header.offset));
                        file.write(reinterpret_cast<char*>(&bmp.dib.biSize), sizeof(bmp.dib.biSize));
                        file.write(reinterpret_cast<char*>(&bmp.dib.biWidth), sizeof(bmp.dib.biWidth));
                        file.write(reinterpret_cast<char*>(&bmp.dib.biHeight), sizeof(bmp.dib.biHeight));
                        file.write(reinterpret_cast<char*>(&bmp.dib.biPlanes), sizeof(bmp.dib.biPlanes));
                        file.write(reinterpret_cast<char*>(&bmp.dib.biBitCount), sizeof(bmp.dib.biBitCount));
                        file.write(reinterpret_cast<char*>(&bmp.dib.biCompression), sizeof(bmp.dib.biCompression));
                        file.write(reinterpret_cast<char*>(&bmp.dib.biSizeImage), sizeof(bmp.dib.biSizeImage));
                        file.write(reinterpret_cast<char*>(&bmp.dib.biXPelsPerMeter), sizeof(bmp.dib.biXPelsPerMeter));
                        file.write(reinterpret_cast<char*>(&bmp.dib.biYPelsPerMeter), sizeof(bmp.dib.biYPelsPerMeter));
                        file.write(reinterpret_cast<char*>(&bmp.dib.biClrUsed), sizeof(bmp.dib.biClrUsed));
                        file.write(reinterpret_cast<char*>(&bmp.dib.biClrImportant), sizeof(bmp.dib.biClrImportant));
                        file.write(reinterpret_cast<char*>(info + 1), bmp.dib.biSizeImage);
                        std::cout << "finished" << std::endl;
                    }

                    GlobalUnlock(dib);
                }
            }

            CloseClipboard();
        }
    }

    return 0;
}

Answer 1

如您所想，保存图像时出错。

我们先分析一下你的代码。

这是截图的图像数据。

请注意：压缩：3 -> BI_BITFIELDS

BI_BITFIELDS: The bitmap is not compressed, and the color table consists of three DWORD (defined in [MS-DTYP] section 2.2.9) color masks that specify the red, green, and blue components, respectively, of each pixel. This is valid when used with 16 and 32-bits per pixel bitmaps.

然后我注意到很少有截图保存为BI_BITFIELDS类型的情况。

包括官方 GDI 示例 -> Capturing an Image

部分代码：

 // 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;

所以建议大家按照官方的例子修改当前代码

最快的解决方案：添加bmp.dib.biCompression = BI_RGB;

在哪里添加？

参考代码：

        if (dib)
        {
            DIB* info = reinterpret_cast<DIB*>(dib);
            BMP bmp = { 0 };
            bmp.header.type = 0x4D42;
            bmp.header.offset = 54;
            bmp.header.bfSize = info->biSizeImage + bmp.header.offset;

            bmp.dib = *info;
            bmp.dib.biCompression = BI_RGB;

            std::cout << "Type: " << std::hex << bmp.header.type << std::dec << "\n";

            ....

屏幕截图和位图的复制部分在结构上有什么区别？

What is the differences in structure between screenshot and copied part of bitmap?

c++

windows

clipboard

winapi