C++将32位BMP图像转换为24位BMP和16位BMP

尝试将32位图像b8r8g8a8转换为24位图像r8g8b8和16位图像r5g5b5。 但结果很奇怪,也许我不明白如何正确地转换图像。如何正确处理和固定颜色?

输入图像:

后 Convert32to16() :

后 Convert32to24() :

标准传真H

// stdafx.h : include file for standard system include files,
// or project specific include files that are used frequently, but
// are changed infrequently
//

#pragma once

#include "targetver.h"

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


// TODO: reference additional headers your program requires here

图像转换器.cpp

#include "stdafx.h"


using std::cout;
using std::endl;
using std::ofstream;
using std::ifstream;

void Convert32to24(void* B8G8R8A8, BYTE* R8G8B8, int width, int height)
{
    long B8G8R8A8Size = (width * height * 4);
    long j = 0;
    for (long i = 0; i < (B8G8R8A8Size - 3); i = i + 4)
    {
        BYTE Red = ((PBYTE)B8G8R8A8)[i + 2];
        BYTE Green = ((PBYTE)B8G8R8A8)[i + 1];
        BYTE Blue = ((PBYTE)B8G8R8A8)[i];
        BYTE Alpha = ((PBYTE)B8G8R8A8)[i + 3];

        R8G8B8[j] = Red;
        R8G8B8[j + 1] = Green;
        R8G8B8[j + 2] = Blue;
        j = j + 3;
    }
}

void Convert32to16(void* B8G8R8A8, BYTE* R5G5B5, int width, int height)
{
    long B8G8R8A8Size = (width * height * 4);

    long j = 0;
    for (long i = 0; i < (B8G8R8A8Size - 3); i = i + 4)
    {
        BYTE Red = ((PBYTE)B8G8R8A8)[i + 2] >> 3;
        BYTE Green = ((PBYTE)B8G8R8A8)[i + 1] >> 3;
        BYTE Blue = ((PBYTE)B8G8R8A8)[i] >> 3;
        BYTE Alpha = ((PBYTE)B8G8R8A8)[i + 3];

        uint16_t RGB565 = ((Red >> 3) << 11) | ((Green >> 2) << 5) | (Blue >> 3);

        R5G5B5[j] = RGB565 >> 8;
        R5G5B5[j + 1] = RGB565 & 0xFF;
        j = j + 2;
    }
}

void WriteDataToBmp(const WCHAR *filename, void *imageData, int width, int height, int BitCount, int bytesPerPixel)
{
    HANDLE hdl = INVALID_HANDLE_VALUE;
    DWORD bytesWritten;
    BITMAPFILEHEADER fileHeader;
    BITMAPINFOHEADER fileInfo;

    fileInfo.biSize = sizeof(BITMAPINFOHEADER);
    fileInfo.biBitCount = BitCount;
    fileInfo.biCompression = BI_RGB;
    fileInfo.biWidth = width;
    fileInfo.biHeight = 0 - height;
    fileInfo.biPlanes = 1;
    fileInfo.biSizeImage = (width * height * bytesPerPixel);

    fileHeader.bfSize = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER) + fileInfo.biSizeImage;
    fileHeader.bfType = 'MB';
    fileHeader.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);

    hdl = CreateFile(filename, GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, 0, NULL);

    if (hdl == INVALID_HANDLE_VALUE)
    {
        return;
    }

    WriteFile(hdl, &fileHeader, sizeof(fileHeader), &bytesWritten, NULL);
    WriteFile(hdl, &fileInfo, sizeof(fileInfo), &bytesWritten, NULL);
    WriteFile(hdl, imageData, fileInfo.biSizeImage, &bytesWritten, NULL);

    CloseHandle(hdl);
}

unsigned char* ReadDataFromBmp(char* filename)
{
    FILE* f = fopen(filename, "rb");
    unsigned char info[54];
    fread(info, sizeof(unsigned char), 54, f);
    int width = *(int*)&info[18];
    int height = *(int*)&info[22];

    int size = abs(4 * width * height);
    unsigned char* data = new unsigned char[size];
    fread(data, sizeof(unsigned char), size, f);
    fclose(f);
    return data;
}

int main(int args, char** cat) {

    int width = 1440;
    int height = 900;

    int bytesOnPixel;
    BYTE *OutputImage24Bit = new BYTE[width * height * 3];
    BYTE *OutputImage16Bit = new BYTE[width * height * 2];
    unsigned char* inputImage32Bit = ReadDataFromBmp((char*)"E:/TestImage.bmp");

    bytesOnPixel = 2;
    Convert32to16(inputImage32Bit, OutputImage16Bit, width, height);
    WriteDataToBmp(L"E:/TestImage16bit.bmp", OutputImage16Bit, width, height, 8 * bytesOnPixel, bytesOnPixel);

    bytesOnPixel = 3;
    Convert32to24(inputImage32Bit, OutputImage24Bit, width, height);
    WriteDataToBmp(L"E:/TestImage24bit.bmp", OutputImage24Bit, width, height, 8 * bytesOnPixel, bytesOnPixel);
    return 1;
}