位图24到32并返回

时间:2012-12-23 14:33:55

标签: c++

这可能是一个很长的帖子,但我真的需要知道如何在24位和32位位图之间进行转换。为了这篇文章的篇幅,我删除了我的问题的PNG部分。

这里是:

我有一个类似下面的结构,它包含所有像素信息:

typedef union RGB
{
    uint32_t Color;
    struct
    {
        unsigned char B, G, R, A;
    } RGBA;
} *PRGB;

std::vector<RGB> Pixels;   //Holds all pixels.

除了24到32之外,所有位图写入都有效,反之亦然。我不知道我做错了什么或为什么24-32转换不起作用。我的位图读写代码如下:

Bitmap(const void* Pointer, int Width, int Height, uint32_t BitsPerPixel) //Constructor initialization here...
{
    Pixels.clear();
    if (Pointer == nullptr) {throw std::logic_error("Null Pointer Exception. Pointer is NULL.");}
    if (Width < 1 || Height < 1) {throw std::invalid_argument("Invalid Arguments. Width and Height cannot equal 0.");}
    std::memset(&Info, 0, sizeof(BITMAPINFO));
    size = ((width * BitsPerPixel + 31) / 32) * 4 * height;

    Info.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
    Info.bmiHeader.biWidth = width;
    Info.bmiHeader.biHeight = height;
    Info.bmiHeader.biPlanes = 1;
    Info.bmiHeader.biBitCount = BitsPerPixel;
    Info.bmiHeader.biCompression = BI_RGB;
    Info.bmiHeader.biSizeImage = size;
    bFileHeader.bfType = 0x4D42;
    bFileHeader.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(Info.bmiHeader);
    bFileHeader.bfSize = bFileHeader.bfOffBits + size;

    const unsigned char* BuffPos = static_cast<const unsigned char*>(Pointer);
    height = (height < 0 ? -height : height);
    Pixels.resize(width * height);

    for (int I = 0; I < height; I++)
    {
        for (int J = 0; J < width; J++)
        {
            Pixels[(height - 1 - I) * width + J].RGBA.B = *(BuffPos++);
            Pixels[(height - 1 - I) * width + J].RGBA.G = *(BuffPos++);
            Pixels[(height - 1 - I) * width + J].RGBA.R = *(BuffPos++);
            Pixels[(height - 1 - I) * width + J].RGBA.A = (Info.bmiHeader.biBitCount > 24 ? *(BuffPos++) : 0);
        }
        if(Info.bmiHeader.biBitCount == 24)
            BuffPos += width % 4;
    }
}

bool SaveBitmap(const char* FilePath)
{
    std::vector<unsigned char> ImageData(size);
    unsigned char* BuffPos = ImageData.data();

    for (int I = 0; I < height; ++I)
    {
        for (int J = 0; J < width; ++J)
        {
            *(BuffPos++) = Pixels[(height - 1 - I) * width + J].RGBA.B;
            *(BuffPos++) = Pixels[(height - 1 - I) * width + J].RGBA.G;
            *(BuffPos++) = Pixels[(height - 1 - I) * width + J].RGBA.R;

            if (Info.bmiHeader.biBitCount > 24)
                *(BuffPos++) = Pixels[(height - 1 - I) * width + J].RGBA.A;
        }
        if(Info.bmiHeader.biBitCount == 24)
            BuffPos += width % 4;
    }

    std::fstream hFile(FilePath, std::fstream::out | std::ofstream::binary);
    if (!hFile.is_open()) return false;

    hFile.write(reinterpret_cast<char*>(&bFileHeader), sizeof(BITMAPFILEHEADER));
    hFile.write(reinterpret_cast<char*>(&Info.bmiHeader), sizeof (BITMAPINFOHEADER));
    hFile.write(reinterpret_cast<char*>(&ImageData[0]), Size());
    hFile.close();

    return true;
}

知道这两个问题可能是什么?我想要它,如果我调用Bitmap(24BmpBuff,W,H,32);它将保存为32.如果我做Bitmap(32BmpBuff,W,H,24)它将保存为24位。我只是看不到它,所以我希望你们中的一个会。

我也尝试过制作帮助函数:

从24位转换为32位。

void T24To32(std::vector<RGB> &Input, std::vector<RGB> &Output, int Width, int Height)
{
    Output.resize(Input.size());
    for (int I = 0; I < Height; ++I)
    {
        for (int J = 0; J < Width; ++J)
        {
            Output[J].RGBA.B = Input[J].RGBA.B;
            Output[J].RGBA.G = Input[J].RGBA.G;
            Output[J].RGBA.R = Input[J].RGBA.R;
            Output[J].RGBA.A = 0;
        }
    }
}

获取像素的unsigned char *并将它们倒置在结构中。

void Pack(int width, int height, int BPP, unsigned char* Input, std::vector<RGB> &Pixels)
{
    unsigned char* BuffPos = Input;
    height = (height < 0 ? -height : height);
    Pixels.resize(width * height);

    for (int I = 0; I < height; I++)
    {
        for (int J = 0; J < width; J++)
        {
            Pixels[(height - 1 - I) * width + J].RGBA.B = *(BuffPos++);
            Pixels[(height - 1 - I) * width + J].RGBA.G = *(BuffPos++);
            Pixels[(height - 1 - I) * width + J].RGBA.R = *(BuffPos++);
            Pixels[(height - 1 - I) * width + J].RGBA.A = (BPP > 24 ? *(BuffPos++) : 0);
        }
        if(BPP == 24)
            BuffPos += width % 4;
    }
}

获取像素结构并将它们直立存储在unsigned char *。

void Unpack(int width, int height, int BPP, std::vector<RGB> Pixels, unsigned char* &Output)
{
    unsigned char* BuffPos = Output;

    for (int I = 0; I < height; ++I)
    {
        for (int J = 0; J < width; ++J)
        {
            *(BuffPos++) = Pixels[(height - 1 - I) * width + J].RGBA.B;
            *(BuffPos++) = Pixels[(height - 1 - I) * width + J].RGBA.G;
            *(BuffPos++) = Pixels[(height - 1 - I) * width + J].RGBA.R;

            if (BPP > 24)
                *(BuffPos++) = Pixels[(height - 1 - I) * width + J].RGBA.A;
        }
        if(BPP == 24)
            BuffPos += width % 4;
    }
}

我使用上述所有内容。输入图像(32位):enter image description here

代码:

void Bitmap32ToBitmap24(int Width, int Height)
{
    Bitmap Image("C:/Images/Bitmap32.bmp");
    std::vector<unsigned char> Pixels(((Width * 32 + 31) / 32) * 4 * Height);   //Array large enough to hold 32 bit bmp.
    unsigned char* BuffPos = Pixels.data();

    Unpack(Width, Height, 32, Image.Get(), BuffPos);                            //Fill the array of unsigned char with image pixels being upright

    Bitmap BMP(Pixels.data(), Width, Height, 24);                               //Convert image to 24 bit bmp and save it.
    BMP.Save("C:/Images/Output/Bitmap32ToBitmap24.png");
}

输出图像(24位):enter image description here 24到32导致: enter image description here

1 个答案:

答案 0 :(得分:1)

在所有代码段中

if(Info.bmiHeader.biBitCount == 24)
        BuffPos += width % 4;

if(BPP == 24)
        BuffPos += width % 4;

发生。我假设这应该为每一行添加填充值。但它不是填充,而是每行的像素数%4。

正确的添加值为(4 - ((width * 3) % 4)) % 4。宽度* 3是该行中的字节数。 %4计算4字节填充的多个字节数,但要填充下一个更高的值,我们需要4 - 这个值。如果不需要填充偏移,则再次为4 - &gt; %4以避免这种情况。

计算相同值的更快方法是(-width * 3) & 3。请参阅wiki