060*_*002 43
你可以尝试这个:
unsigned char* readBMP(char* filename)
{
int i;
FILE* f = fopen(filename, "rb");
unsigned char info[54];
fread(info, sizeof(unsigned char), 54, f); // read the 54-byte header
// extract image height and width from header
int width = *(int*)&info[18];
int height = *(int*)&info[22];
int size = 3 * width * height;
unsigned char* data = new unsigned char[size]; // allocate 3 bytes per pixel
fread(data, sizeof(unsigned char), size, f); // read the rest of the data at once
fclose(f);
for(i = 0; i < size; i += 3)
{
unsigned char tmp = data[i];
data[i] = data[i+2];
data[i+2] = tmp;
}
return data;
}
现在data应该包含像素的(R,G,B)值.像素(i,j)的颜色存储在data[3 * (i * width + j)],data[3 * (i * width + j) + 1]和data[3 * (i * width + j) + 2].
在最后一部分中,完成每个第一和第三像素之间的交换,因为窗口将颜色值存储为(B,G,R)三元组,而不是(R,G,B).
Krz*_*arz 16
填充修复后的readBMP函数代码:
unsigned char* ReadBMP(char* filename)
{
int i;
FILE* f = fopen(filename, "rb");
if(f == NULL)
throw "Argument Exception";
unsigned char info[54];
fread(info, sizeof(unsigned char), 54, f); // read the 54-byte header
// extract image height and width from header
int width = *(int*)&info[18];
int height = *(int*)&info[22];
cout << endl;
cout << " Name: " << filename << endl;
cout << " Width: " << width << endl;
cout << "Height: " << height << endl;
int row_padded = (width*3 + 3) & (~3);
unsigned char* data = new unsigned char[row_padded];
unsigned char tmp;
for(int i = 0; i < height; i++)
{
fread(data, sizeof(unsigned char), row_padded, f);
for(int j = 0; j < width*3; j += 3)
{
// Convert (B, G, R) to (R, G, B)
tmp = data[j];
data[j] = data[j+2];
data[j+2] = tmp;
cout << "R: "<< (int)data[j] << " G: " << (int)data[j+1]<< " B: " << (int)data[j+2]<< endl;
}
}
fclose(f);
return data;
}
我无法对顶级答案发表评论，因为我还没有足够的 stackoverflow 代表，但我只是想指出该实现中的一个非常关键的错误。
某些位图可以使用负高度写入，因此当您尝试分配图像数据缓冲区时，您的代码将崩溃std::bad_alloc。负高度的位图意味着图像数据是从上到下存储的，而不是传统的从下到上存储的。因此，顶层答案的一个稍微更好的版本是（仍然不包括具有不同字节序和字节大小的系统的可移植性）：
unsigned char* readBMP(char* filename)
{
int i;
FILE* f = fopen(filename, "rb");
unsigned char info[54];
fread(info, sizeof(unsigned char), 54, f); // read the 54-byte header
// extract image height and width from header
int width, height;
memcpy(&width, info + 18, sizeof(int));
memcpy(&height, info + 22, sizeof(int));
int heightSign = 1;
if (height < 0){
heightSign = -1;
}
int size = 3 * width * abs(height);
unsigned char* data = new unsigned char[size]; // allocate 3 bytes per pixel
fread(data, sizeof(unsigned char), size, f); // read the rest of the data at once
fclose(f);
if(heightSign == 1){
for(i = 0; i < size; i += 3)
{
//code to flip the image data here....
}
}
return data;
}
我创建了一个BitMap类，该类适用于每个像素具有24位的bmp文件。如果bmp不兼容，则应该得到一个相关的错误。
几乎与Wikipedia文章完全相同。（一个问题是，它不适用于像素数组偏移量大于255的文件。这在代码中已指出，应易于修复。）
我一直在使用mspaint创建的bmp文件。
这是一个示例用法
example.cpp
#include "bmp.h"
int main() {
// load the file. The constructor now does most of the work
BitMap example_bmp("examplefile.bmp");
// get the vector <R,G,B> for the pixel at (1,1)
std::vector<unsigned int> example_vector = example_bmp.getPixel(1,1);
}
example_vector现在包含从图像顶部开始向下索引的坐标（1,1）处像素的rgb（按此顺序）值。索引从0开始。请参阅Wikipedia示例。
这是头文件：
#ifndef BMP_H
#define BMP_H
#include <iostream>
#include <vector>
#include <fstream>
class BitMap {
private:
unsigned char m_bmpFileHeader[14];
unsigned int m_pixelArrayOffset;
unsigned char m_bmpInfoHeader[40];
int m_height;
int m_width;
int m_bitsPerPixel;
int m_rowSize;
int m_pixelArraySize;
unsigned char* m_pixelData;
char * m_copyname;
const char * m_filename;
public:
BitMap(const char * filename);
~BitMap();
std::vector<unsigned int> getPixel(int i,int j);
void makeCopy(char * filename);
void writePixel(int i,int j, int R, int G, int B);
void swapPixel(int i, int j, int i2, int j2);
void dispPixelData();
int width() {return m_width;}
int height() {return m_height;}
int vd(int i, int j);
int hd(int i, int j);
bool isSorted();
};
BitMap::BitMap( const char * filename) {
using namespace std;
m_filename = filename;
ifstream inf(filename);
if(!inf) {
cerr<<"Unable to open file: "<<filename<<"\n";
}
//unsigned char m_bmpFileHeader[14];
unsigned char a;
for(int i =0;i<14;i++) {
inf>>hex>>a;
m_bmpFileHeader[i] = a;
}
if(m_bmpFileHeader[0]!='B' || m_bmpFileHeader[1]!='M') {
cerr<<"Your info header might be different!\nIt should start with 'BM'.\n";
}
/*
THE FOLLOWING LINE ONLY WORKS IF THE OFFSET IS 1 BYTE!!!!! (it can be 4 bytes max)
That should be fixed now.
old line was
m_pixelArrayOffset = m_bmpFileHeader[10];
*/
unsigned int * array_offset_ptr = (unsigned int *)(m_bmpFileHeader + 10);
m_pixelArrayOffset = *array_offset_ptr;
if( m_bmpFileHeader[11] != 0 || m_bmpFileHeader[12] !=0 || m_bmpFileHeader[13] !=0 ) {
std::cerr<< "You probably need to fix something. bmp.h("<<__LINE__<<")\n";
}
//unsigned char m_bmpInfoHeader[40];
for(int i=0;i<40;i++) {
inf>>hex>>a;
m_bmpInfoHeader[i]=a;
}
int * width_ptr = (int*)(m_bmpInfoHeader+4);
int * height_ptr = (int*)(m_bmpInfoHeader+8);
m_width = *width_ptr;
m_height = *height_ptr;
printf("W: %i, H: %i", m_width, m_height);
m_bitsPerPixel = m_bmpInfoHeader[14];
if(m_bitsPerPixel!=24) {
cerr<<"This program is for 24bpp files. Your bmp is not that\n";
}
int compressionMethod = m_bmpInfoHeader[16];
if(compressionMethod!=0) {
cerr<<"There's some compression stuff going on that we might not be able to deal with.\n";
cerr<<"Comment out offending lines to continue anyways. bpm.h line: "<<__LINE__<<"\n";
}
m_rowSize = int( floor( (m_bitsPerPixel*m_width + 31.)/32 ) ) *4;
m_pixelArraySize = m_rowSize* abs(m_height);
m_pixelData = new unsigned char [m_pixelArraySize];
inf.seekg(m_pixelArrayOffset,ios::beg);
for(int i=0;i<m_pixelArraySize;i++) {
inf>>hex>>a;
m_pixelData[i]=a;
}
}
BitMap::~BitMap() {
delete[] m_pixelData;
}
void BitMap::dispPixelData() {
for(int i=0;i<m_pixelArraySize;i++) {
std::cout<<(unsigned int)m_pixelData[i]<<" ";
}
std::cout<<"\n";
}
// output is in rgb order.
std::vector<unsigned int> BitMap::getPixel(int x, int y) {
if(x<m_width && y<m_height) {
std::vector<unsigned int> v;
v.push_back(0);
v.push_back(0);
v.push_back(0);
y = m_height -1- y; //to flip things
//std::cout<<"y: "<<y<<" x: "<<x<<"\n";
v[0] = (unsigned int) ( m_pixelData[ m_rowSize*y+3*x+2 ] ); //red
v[1] = (unsigned int) ( m_pixelData[ m_rowSize*y+3*x+1 ] ); //greed
v[2] = (unsigned int) ( m_pixelData[ m_rowSize*y+3*x+0 ] ); //blue
return v;
}
else {std::cerr<<"BAD INDEX\n";std::cerr<<"X: "<<x<<" Y: "<<y<<"\n";}
}
void BitMap::makeCopy(char * filename) {
std::ofstream copyfile(filename);
std::ifstream infile(m_filename);
m_copyname = filename;
unsigned char c;
while(infile) {
infile>>c;
copyfile<<c;
}
}
// changes the file
void BitMap::writePixel(int x,int y, int R, int G, int B) {
std::fstream file(m_filename);
y = m_height -1- y; // to flip things.
int blueOffset = m_pixelArrayOffset+m_rowSize*y+3*x+0;
// writes to the file
file.seekg(blueOffset,std::ios::beg);
file<< (unsigned char)B;
file.seekg(blueOffset+1,std::ios::beg);
file<< (unsigned char)G;
file.seekg(blueOffset+2,std::ios::beg);
file<< (unsigned char)R;
// edits data in pixelData array
m_pixelData[m_rowSize*y+3*x+2] = (unsigned char)R;
m_pixelData[m_rowSize*y+3*x+1] = (unsigned char)G;
m_pixelData[m_rowSize*y+3*x+0] = (unsigned char)B;
}
// changes the file
void BitMap::swapPixel(int i, int j, int i2, int j2) {
std::vector<unsigned int> p1 = (*this).getPixel(i,j);
std::vector<unsigned int> p2 = (*this).getPixel(i2,j2);
(*this).writePixel(i,j,p2[0],p2[1],p2[2]);
(*this).writePixel(i2,j2,p1[0],p1[1],p1[2]);
}
#endif
这是一个有效的C++版本的答案:
#include <fstream>
#include <iostream>
#include <string>
#include <array>
#include <vector>
#include <iterator>
std::vector<char> readBMP(const std::string &file)
{
static constexpr size_t HEADER_SIZE = 54;
std::ifstream bmp(file, std::ios::binary);
std::array<char, HEADER_SIZE> header;
bmp.read(header.data(), header.size());
auto fileSize = *reinterpret_cast<uint32_t *>(&header[2]);
auto dataOffset = *reinterpret_cast<uint32_t *>(&header[10]);
auto width = *reinterpret_cast<uint32_t *>(&header[18]);
auto height = *reinterpret_cast<uint32_t *>(&header[22]);
auto depth = *reinterpret_cast<uint16_t *>(&header[28]);
std::cout << "fileSize: " << fileSize << std::endl;
std::cout << "dataOffset: " << dataOffset << std::endl;
std::cout << "width: " << width << std::endl;
std::cout << "height: " << height << std::endl;
std::cout << "depth: " << depth << "-bit" << std::endl;
std::vector<char> img(dataOffset - HEADER_SIZE);
bmp.read(img.data(), img.size());
auto dataSize = ((width * 3 + 3) & (~3)) * height;
img.resize(dataSize);
bmp.read(img.data(), img.size());
char temp = 0;
for (auto i = dataSize - 4; i >= 0; i -= 3)
{
temp = img[i];
img[i] = img[i+2];
img[i+2] = temp;
std::cout << "R: " << int(img[i] & 0xff) << " G: " << int(img[i+1] & 0xff) << " B: " << int(img[i+2] & 0xff) << std::endl;
}
return img;
}