Разбор кода. Преобразование числа в цвет пикселя. Что такое data в изображениях

Что такое data для изображения? В данном коде это количество пикселей на битностЬ цвета (точно не знаю как это называется)

TGAImage::TGAImage(const TGAImage &img) {
    width = img.width;
    height = img.height;
    bytespp = img.bytespp;
    unsigned long nbytes = width*height*bytespp;
    data = new unsigned char[nbytes];
    memcpy(data, img.data, nbytes);
}

но для чего нужна эта data?

Автор статmи отдает такое огромное число в TGAColor, но как оно преобразуется в цвет.

TGAColor TGAImage::get(int x, int y) {
    if (!data || x<0 || y<0 || x>=width || y>=height) {
        return TGAColor();
    }
    return TGAColor(data+(x+y*width)*bytespp, bytespp);
}

вот два файла. tgaimage.cpp

#include <iostream>
#include <fstream>
#include <string.h>
#include <time.h>
#include <math.h>
#include "tgaimage.h"
TGAImage::TGAImage() : data(NULL), width(0), height(0), bytespp(0) {
}
TGAImage::TGAImage(int w, int h, int bpp) : data(NULL), width(w), height(h), bytespp(bpp) {
    unsigned long nbytes = width*height*bytespp;
    data = new unsigned char[nbytes];
    memset(data, 0, nbytes);
}
TGAImage::TGAImage(const TGAImage &img) {
    width = img.width;
    height = img.height;
    bytespp = img.bytespp;
    unsigned long nbytes = width*height*bytespp;
    data = new unsigned char[nbytes];
    memcpy(data, img.data, nbytes);
}
TGAImage::~TGAImage() {
    if (data) delete [] data;
}
TGAImage & TGAImage::operator =(const TGAImage &img) {
    if (this != &img) {
        if (data) delete [] data;
        width  = img.width;
        height = img.height;
        bytespp = img.bytespp;
        unsigned long nbytes = width*height*bytespp;
        data = new unsigned char[nbytes];
        memcpy(data, img.data, nbytes);
    }
    return *this;
}
bool TGAImage::read_tga_file(const char *filename) {
    if (data) delete [] data;
    data = NULL;
    std::ifstream in;
    in.open (filename, std::ios::binary);
    if (!in.is_open()) {
        std::cerr << "can't open file " << filename << "\n";
        in.close();
        return false;
    }
    TGA_Header header;
    in.read((char *)&header, sizeof(header));
    if (!in.good()) {
        in.close();
        std::cerr << "an error occured while reading the header\n";
        return false;
    }
    width   = header.width;
    height  = header.height;
    bytespp = header.bitsperpixel>>3;
    if (width<=0 || height<=0 || (bytespp!=GRAYSCALE && bytespp!=RGB && bytespp!=RGBA)) {
        in.close();
        std::cerr << "bad bpp (or width/height) value\n";
        return false;
    }
    unsigned long nbytes = bytespp*width*height;
    data = new unsigned char[nbytes];
    if (3==header.datatypecode || 2==header.datatypecode) {
        in.read((char *)data, nbytes);
        if (!in.good()) {
            in.close();
            std::cerr << "an error occured while reading the data\n";
            return false;
        }
    } else if (10==header.datatypecode||11==header.datatypecode) {
        if (!load_rle_data(in)) {
            in.close();
            std::cerr << "an error occured while reading the data\n";
            return false;
        }
    } else {
        in.close();
        std::cerr << "unknown file format " << (int)header.datatypecode << "\n";
        return false;
    }
    if (!(header.imagedescriptor & 0x20)) {
        flip_vertically();
    }
    if (header.imagedescriptor & 0x10) {
        flip_horizontally();
    }
    std::cerr << width << "x" << height << "/" << bytespp*8 << "\n";
    in.close();
    return true;
}
bool TGAImage::load_rle_data(std::ifstream &in) {
    unsigned long pixelcount = width*height;
    unsigned long currentpixel = 0;
    unsigned long currentbyte  = 0;
    TGAColor colorbuffer;
    do {
        unsigned char chunkheader = 0;
        chunkheader = in.get();
        if (!in.good()) {
            std::cerr << "an error occured while reading the data\n";
            return false;
        }
        if (chunkheader<128) {
            chunkheader++;
            for (int i=0; i<chunkheader; i++) {
                in.read((char *)colorbuffer.raw, bytespp);
                if (!in.good()) {
                    std::cerr << "an error occured while reading the header\n";
                    return false;
                }
                for (int t=0; t<bytespp; t++)
                    data[currentbyte++] = colorbuffer.raw[t];
                currentpixel++;
                if (currentpixel>pixelcount) {
                    std::cerr << "Too many pixels read\n";
                    return false;
                }
            }
        } else {
            chunkheader -= 127;
            in.read((char *)colorbuffer.raw, bytespp);
            if (!in.good()) {
                std::cerr << "an error occured while reading the header\n";
                return false;
            }
            for (int i=0; i<chunkheader; i++) {
                for (int t=0; t<bytespp; t++)
                    data[currentbyte++] = colorbuffer.raw[t];
                currentpixel++;
                if (currentpixel>pixelcount) {
                    std::cerr << "Too many pixels read\n";
                    return false;
                }
            }
        }
    } while (currentpixel < pixelcount);
    return true;
}
bool TGAImage::write_tga_file(const char *filename, bool rle) {
    unsigned char developer_area_ref[4] = {0, 0, 0, 0};
    unsigned char extension_area_ref[4] = {0, 0, 0, 0};
    unsigned char footer[18] = {'T','R','U','E','V','I','S','I','O','N','-','X','F','I','L','E','.','\0'};
    std::ofstream out;
    out.open (filename, std::ios::binary);
    if (!out.is_open()) {
        std::cerr << "can't open file " << filename << "\n";
        out.close();
        return false;
    }
    TGA_Header header;
    memset((void *)&header, 0, sizeof(header));
    header.bitsperpixel = bytespp<<3;
    header.width  = width;
    header.height = height;
    header.datatypecode = (bytespp==GRAYSCALE?(rle?11:3):(rle?10:2));
    header.imagedescriptor = 0x20; // top-left origin
    out.write((char *)&header, sizeof(header));
    if (!out.good()) {
        out.close();
        std::cerr << "can't dump the tga file\n";
        return false;
    }
    if (!rle) {
        out.write((char *)data, width*height*bytespp);
        if (!out.good()) {
            std::cerr << "can't unload raw data\n";
            out.close();
            return false;
        }
    } else {
        if (!unload_rle_data(out)) {
            out.close();
            std::cerr << "can't unload rle data\n";
            return false;
        }
    }
    out.write((char *)developer_area_ref, sizeof(developer_area_ref));
    if (!out.good()) {
        std::cerr << "can't dump the tga file\n";
        out.close();
        return false;
    }
    out.write((char *)extension_area_ref, sizeof(extension_area_ref));
    if (!out.good()) {
        std::cerr << "can't dump the tga file\n";
        out.close();
        return false;
    }
    out.write((char *)footer, sizeof(footer));
    if (!out.good()) {
        std::cerr << "can't dump the tga file\n";
        out.close();
        return false;
    }
    out.close();
    return true;
}
// TODO: it is not necessary to break a raw chunk for two equal pixels (for the matter of the resulting size)
bool TGAImage::unload_rle_data(std::ofstream &out) {
    const unsigned char max_chunk_length = 128;
    unsigned long npixels = width*height;
    unsigned long curpix = 0;
    while (curpix<npixels) {
        unsigned long chunkstart = curpix*bytespp;
        unsigned long curbyte = curpix*bytespp;
        unsigned char run_length = 1;
        bool raw = true;
        while (curpix+run_length<npixels && run_length<max_chunk_length) {
            bool succ_eq = true;
            for (int t=0; succ_eq && t<bytespp; t++) {
                succ_eq = (data[curbyte+t]==data[curbyte+t+bytespp]);
            }
            curbyte += bytespp;
            if (1==run_length) {
                raw = !succ_eq;
            }
            if (raw && succ_eq) {
                run_length--;
                break;
            }
            if (!raw && !succ_eq) {
                break;
            }
            run_length++;
        }
        curpix += run_length;
        out.put(raw?run_length-1:run_length+127);
        if (!out.good()) {
            std::cerr << "can't dump the tga file\n";
            return false;
        }
        out.write((char *)(data+chunkstart), (raw?run_length*bytespp:bytespp));
        if (!out.good()) {
            std::cerr << "can't dump the tga file\n";
            return false;
        }
    }
    return true;
}
TGAColor TGAImage::get(int x, int y) {
    if (!data || x<0 || y<0 || x>=width || y>=height) {
        return TGAColor();
    }
    return TGAColor(data+(x+y*width)*bytespp, bytespp);
}
bool TGAImage::set(int x, int y, TGAColor c) {
    if (!data || x<0 || y<0 || x>=width || y>=height) {
        return false;
    }
    memcpy(data+(x+y*width)*bytespp, c.raw, bytespp);
    return true;
}
int TGAImage::get_bytespp() {
    return bytespp;
}
int TGAImage::get_width() {
    return width;
}
int TGAImage::get_height() {
    return height;
}
bool TGAImage::flip_horizontally() {
    if (!data) return false;
    int half = width>>1;
    for (int i=0; i<half; i++) {
        for (int j=0; j<height; j++) {
            TGAColor c1 = get(i, j);
            TGAColor c2 = get(width-1-i, j);
            set(i, j, c2);
            set(width-1-i, j, c1);
        }
    }
    return true;
}
bool TGAImage::flip_vertically() {
    if (!data) return false;
    unsigned long bytes_per_line = width*bytespp;
    unsigned char *line = new unsigned char[bytes_per_line];
    int half = height>>1;
    for (int j=0; j<half; j++) {
        unsigned long l1 = j*bytes_per_line;
        unsigned long l2 = (height-1-j)*bytes_per_line;
        memmove((void *)line,      (void *)(data+l1), bytes_per_line);
        memmove((void *)(data+l1), (void *)(data+l2), bytes_per_line);
        memmove((void *)(data+l2), (void *)line,      bytes_per_line);
    }
    delete [] line;
    return true;
}
unsigned char *TGAImage::buffer() {
    return data;
}
void TGAImage::clear() {
    memset((void *)data, 0, width*height*bytespp);
}
bool TGAImage::scale(int w, int h) {
    if (w<=0 || h<=0 || !data) return false;
    unsigned char *tdata = new unsigned char[w*h*bytespp];
    int nscanline = 0;
    int oscanline = 0;
    int erry = 0;
    unsigned long nlinebytes = w*bytespp;
    unsigned long olinebytes = width*bytespp;
    for (int j=0; j<height; j++) {
        int errx = width-w;
        int nx   = -bytespp;
        int ox   = -bytespp;
        for (int i=0; i<width; i++) {
            ox += bytespp;
            errx += w;
            while (errx>=(int)width) {
                errx -= width;
                nx += bytespp;
                memcpy(tdata+nscanline+nx, data+oscanline+ox, bytespp);
            }
        }
        erry += h;
        oscanline += olinebytes;
        while (erry>=(int)height) {
            if (erry>=(int)height<<1) // it means we jump over a scanline
                memcpy(tdata+nscanline+nlinebytes, tdata+nscanline, nlinebytes);
            erry -= height;
            nscanline += nlinebytes;
        }
    }
    delete [] data;
    data = tdata;
    width = w;
    height = h;
    return true;
}

вот tgaimage.h

#ifndef __IMAGE_H__
#define __IMAGE_H__
#include <fstream>
#pragma pack(push,1)
struct TGA_Header {
    char idlength;
    char colormaptype;
    char datatypecode;
    short colormaporigin;
    short colormaplength;
    char colormapdepth;
    short x_origin;
    short y_origin;
    short width;
    short height;
    char  bitsperpixel;
    char  imagedescriptor;
};
#pragma pack(pop)

struct TGAColor {
    union {
        struct {
            unsigned char b, g, r, a;
        };
        unsigned char raw[4];
        unsigned int val;
    };
    int bytespp;
    TGAColor() : val(0), bytespp(1) {
    }
    TGAColor(unsigned char R, unsigned char G, unsigned char B, unsigned char A=255) : b(B), g(G), r(R), a(A), bytespp(4) {
    }
    TGAColor(int v, int bpp) : val(v), bytespp(bpp) {
    }
    TGAColor(const TGAColor &c) : val(c.val), bytespp(c.bytespp) {
    }
    TGAColor(const unsigned char *p, int bpp) : val(0), bytespp(bpp) {
        for (int i=0; i<bpp; i++) {
            raw[i] = p[i];
        }
    }
    TGAColor & operator =(const TGAColor &c) {
        if (this != &c) {
            bytespp = c.bytespp;
            val = c.val;
        }
        return *this;
    }
};

class TGAImage {
protected:
    unsigned char* data;
    int width;
    int height;
    int bytespp;
    bool   load_rle_data(std::ifstream &in);
    bool unload_rle_data(std::ofstream &out);
public:
    enum Format {
        GRAYSCALE=1, RGB=3, RGBA=4
    };
    TGAImage();
    TGAImage(int w, int h, int bpp);
    TGAImage(const TGAImage &img);
    bool read_tga_file(const char *filename);
    bool write_tga_file(const char *filename, bool rle=true);
    bool flip_horizontally();
    bool flip_vertically();
    bool scale(int w, int h);
    TGAColor get(int x, int y);
    bool set(int x, int y, TGAColor c);
    ~TGAImage();
    TGAImage & operator =(const TGAImage &img);
    int get_width();
    int get_height();
    int get_bytespp();
    unsigned char *buffer();
    void clear();
};
#endif //__IMAGE_H__