Read RGB from bitmap - wrong values (of RGB); c++

Question

I want to read the RGB values of all pixels from a BMP file. I have code in c++, which look like:

#include <iostream>
#include <fstream>

using namespace std;

int main () {
    FILE *streamIn;
    streamIn = fopen("./Untitled.bmp", "r");
    if (streamIn == (FILE *)0) {
        printf("File opening error ocurred. Exiting program.\n");
        return 0;
    }

    unsigned char info[54];
    fread(info, sizeof(unsigned char), 54, streamIn);

    int width = *(int*)&info[18];
    int height = *(int*)&info[22];

    int image[width*height][3];
    int i = 0;

    for(i=0;i<width*height;i++) {
        image[i][2] = getc(streamIn);
        image[i][1] = getc(streamIn);
        image[i][0] = getc(streamIn);
        printf("pixel %d : [%d,%d,%d]\n",i+1,image[i][0],image[i][1],image[i][2]);
    }

    fclose(streamIn);

    return 0;
}

and an image like this (grid overlaid):

which are 6x12 pixels file with two colors - black and white.

I try to find out why after executing the above code with the image as a parameter I don't get just pixels with RGB: [0,0,0] and [255,255,255] but also [0,248,0], [7,224,0] and others.

Hex dump of that file is:

0000-0010:  42 4d 9a 01-00 00 00 00-00 00 7a 00-00 00 6c 00  BM...... ..z...l.
0000-0020:  00 00 08 00-00 00 0c 00-00 00 01 00-18 00 00 00  ........ ........
0000-0030:  00 00 20 01-00 00 13 0b-00 00 13 0b-00 00 00 00  ........ ........
0000-0040:  00 00 00 00-00 00 42 47-52 73 00 00-00 00 00 00  ......BG Rs......
0000-0050:  00 00 00 00-00 00 00 00-00 00 00 00-00 00 00 00  ........ ........
0000-0060:  00 00 00 00-00 00 00 00-00 00 00 00-00 00 00 00  ........ ........
0000-0070:  00 00 00 00-00 00 00 00-00 00 02 00-00 00 00 00  ........ ........
0000-0080:  00 00 00 00-00 00 00 00-00 00 ff ff-ff ff ff ff  ........ ........
0000-0090:  ff ff ff ff-ff ff ff ff-ff ff ff ff-ff ff ff ff  ........ ........
0000-00a0:  ff ff ff ff-ff 00 00 00-00 00 00 00-00 00 00 00  ........ ........
0000-00b0:  00 00 00 00-00 00 00 ff-ff ff ff ff-ff 00 00 00  ........ ........
0000-00c0:  00 00 00 00-00 00 00 00-00 00 00 00-00 00 00 ff  ........ ........
0000-00d0:  ff ff ff ff-ff ff ff ff-ff ff ff ff-ff ff ff ff  ........ ........
0000-00e0:  ff ff ff ff-ff ff ff ff-ff ff ff ff-ff ff ff ff  ........ ........
0000-00f0:  ff ff ff ff-ff ff ff ff-ff ff ff ff-ff ff ff ff  ........ ........
0000-0100:  ff ff ff ff-ff ff ff ff-ff ff ff ff-ff ff ff ff  ........ ........
0000-0110:  ff ff ff ff-ff ff ff ff-ff ff ff ff-ff ff ff ff  ........ ........
0000-0120:  ff ff ff ff-ff ff ff ff-ff ff ff ff-ff ff ff ff  ........ ........
0000-0130:  ff ff ff ff-ff ff ff ff-ff ff ff ff-ff ff ff ff  ........ ........
0000-0140:  ff ff ff ff-ff ff ff ff-ff ff ff ff-ff ff ff ff  ........ ........
0000-0150:  ff ff ff ff-ff ff ff ff-ff ff ff ff-ff ff ff ff  ........ ........
0000-0160:  ff ff ff ff-ff ff ff ff-ff ff ff ff-ff ff ff ff  ........ ........
0000-0170:  ff ff ff ff-ff ff ff ff-ff ff ff ff-ff ff ff ff  ........ ........
0000-0180:  ff ff ff ff-ff ff ff ff-ff ff ff ff-ff ff ff ff  ........ ........
0000-0190:  ff ff 00 00-00 ff ff ff-00 00 00 ff-ff ff 00 00  ........ ........
0000-019a:  00 ff ff ff-00 00 00 ff-ff ff                    ........ ..

File size is 410 bytes. It should be 270 (6*12*3 + 54). That means that there is some extra information in this file.

Answer 1

Your Bitmap file consists:

Bitmap File Header: 14 Bytes
42 4d 9a 01-00 00 00 00-00 00 7a 00-00 00

The last 4 bytes is the offset of where rgb values begin, 7A = after 122 Bytes

DIB header The first 4 bytes is the size:
6c 00 00 00 -> 108 Bytes so BITMAPV4HEADER

The next 8 Bytes are the width and height in pixels:
08 00-00 00 0c 00-00 00 width height each 4 Bytes

So your bitmap is not 6x12 but 8x12! There is no need for padding because 8x3 = 24 which is multiple of 4.

The actual pixels are from 0x7A - 0x199 Beginning from the last row and going upwards, from left to right, the bitmap is:

The file size is correct:

file size = Bitmap File Header + DIB header + rgb Bytes = 14 + 108 + 8 * 12 * 3 = 410

To read a specific pixel in your image:

Load the whole bitmap file

char *buff;
char rgb[8 * 12 * 3]; //for simplicity
fptr = fopen("....bmp", "rb");

fseek(fptr, 0, SEEK_END);
int file_Size = ftell(fptr);
fseek(fptr, 0, SEEK_SET);

buff = malloc(file_Size * sizeof(char));

fread(buff, sizeof(char), file_Size, fptr);

memmove(rgb, buff[0x7A], 8 * 12 * 3);

Now rgb contains the actual pixels but the order is left->right and down->up meaning the first pixel is the one at the left bottom of the image.