我有一个练习，我需要读取PPM文件并将其内容保存为C ++中的图像。然后我想计算平均亮度。我有3个头文件。我设法读取文件并检查P6值，宽度，高度和深度。如何从文件中提取图像数据以制作图像对象以计算平均亮度？
Color.h
namespace imaging
{
/*! An alias for the floating point representation of color components (32bit per color channel).
*/
typedef float component_t;
class Color
{
public:
// members
component_t r,
g,
b;
// member functions
component_t & operator [] (size_t index)
{
return *(&r + index);
}
Color operator + (Color & right)
{
Color left;
left.r = r + right.r;
left.g = g + right.g;
left.b = b + right.b;
return left;
}
// constructors
Color(component_t r, component_t g, component_t b) : r(r), g(g), b(b) {}
Color() : r(0), g(0), b(0) {}
};
image.h的
namespace imaging {
class Image
{
public:
enum channel_t {RED=0,GREEN, BLUE};
protected:
component_t * buffer;
unsigned int width,
height;
public:
// metric accessors
const unsigned int getWidth() const {return width;}
const unsigned int getHeight() const {return height;}
// data accessors
component_t * getRawDataPtr();
Color getPixel(unsigned int x, unsigned int y) const;
// data mutators
void setPixel(unsigned int x, unsigned int y, Color & value);
void setData(const component_t * & data_ptr);
void resize(unsigned int new_width, unsigned int new_height);
// constructors and destructor
/*! Default constructor.
*/
Image();
/*! Constructor with width and height specification.
*
*/
Image(unsigned int width, unsigned int height);
// Constructor with data initialization
Image(unsigned int width, unsigned int height, const component_t * data_ptr);
/*! Copy constructor.
*/
Image(const Image &src);
/*! The Image destructor.
*/
~Image();
/*! Copy assignment operator.*/
Image & operator = (const Image & right);
};
}
ppm_format.h
namespace imaging
{
/*! Reads a PPM image file and returns a pointer to a newly allocated Image object containing the image.
*/
Image * ReadPPM(const char * filename);
} //namespace imaging
我为读取PPM文件方法编写了这段代码：
Image * ReadPPM(const char* filename) {
ifstream ifs;
string v1; //for the P6 value
int v2,v3,v4; //for width, height and color depth
cin.getline(filename, 20);
ifs.open(filename,ios::binary);
if (ifs.is_open()) {
while (ifs.good()){
if (ifs>>v1>>v2>>v3>>v4){
int height = v2;
int width = v3;
if (v1!="P6") {
cout<<"Unsupported type of ppm file(not P6)"<<endl;
ifs.close();
exit(0);
}
if (v2<1){
cout<<"Unsupported width"<<endl;
ifs.close();
exit(0);
}
if (v3<1){
cout<<"Unsupported height"<<endl;
ifs.close();
exit(0);
}
if (v4<1 || v4>255){
cout<<"Unsupported number of bits"<<endl;
ifs.close();
exit(0);
}
//cout<<v1<<endl<<height<<endl<<width;
}
}
}
else if (!ifs.is_open()) {
cout<<"The file with name: "<<filename<<" does not exist";
exit(EXIT_FAILURE);
}
ifs.close();
// end of reading the file
//start making the image
Image image = new Image(v2,v3);
return image;
}
我写了这段代码用于阅读和保存图像数据。问题是我想将图像数据提取为component_t类型（浮点数）
char* data = new char[3*height*width];
int bytesPerLn = width*3;
for (int i=0;i<height;i++){
char* tmp = new char[bytesPerLn];
ifs.getline(tmp,bytesPerLn);
cout<<tmp;
strcat(data,tmp);
}
cout<<data;