Trouble getting the (int) value of a header byte from a bmp image when it is bigger than 127 pixels

Question

I'm trying to get the size of a generic.bmp. However, when the image is bigger than 127 pixels, the bytes become weird. (I'm opening the images with a text editor then pasting the contents in an online character-to-text converter because when in this situation my C# program will just print a "0".) Here are the relevant bytes for a 127-tall image:

127 032 032 032

Clearly, the image is 127 pixels tall.

Here are the relevant bytes for a 128-tall image:

226 130 172 032 032 032

What happened here? If 128 is the limit, shouldn't it become "0 1 032 032"? My thinking is that the value in the data would be something like 226*(base^0) + 130*(base^1) + 172*(base^2), but I think that would be at least greater than 226. Thank you for reading.

Edit: I checked the hex values instead (with Notepad++), and the number seems right. But why does it become messed up when transformed to an integer (for this I use C#'s what I believe to be called "typecasting", "(int)")?

string line;
try
{
    StreamReader sr = new StreamReader("E:\\Test15.bmp");
    line = sr.ReadLine();
    while (line != null)
    {
        for(int i=0; i<line.Length; i++)
        {
            if(i==0)
            {
                Console.WriteLine("Header");
                Console.Write("\tSignature: ");
            }
            if(i==2)
            {
                Console.WriteLine();
                Console.Write("\tFile size: ");
            }
            if(i==6)
            {
                Console.WriteLine();
                Console.Write("\tReserved: ");
            }
            if(i==10)
            {
                Console.WriteLine();
                Console.Write("\tData offset: ");
            }
            if(i==14)
            {
                Console.WriteLine();
                Console.WriteLine();
                Console.WriteLine("Info header:");
                Console.Write("\tHeader size: ");
            }
            if(i==18)
            {
                Console.WriteLine();
                Console.Write("\tImage width: ");
            }
            if (i == 22)
            {
                Console.WriteLine();
                Console.Write("\tImage height: ");
            }
            if (i == 26)
            {
                Console.WriteLine();
                Console.Write("\tNumber of color planes: ");
            }
            if (i == 28)
            {
                Console.WriteLine();
                Console.Write("\tBits per pixel: ");
            }
            if(i==30)
            {
                Console.WriteLine();
                Console.Write("\tCompression: ");
            }
            if(i==34)
            {
                Console.WriteLine();
                Console.Write("\tImage size: ");
            }
            if(i==38)
            {
                Console.WriteLine();
                Console.Write("\tX resolution: ");
            }
            if (i == 42)
            {
                Console.WriteLine();
                Console.Write("\tY resolution: ");
            }
            if (i == 46)
            {
                Console.WriteLine();
                Console.Write("\tPixels per meter: ");
            }
            if (i == 50)
            {
                Console.WriteLine();
                Console.Write("\tNumber of colors: ");
            }
            if (i == 54)
            {
                Console.WriteLine();
                Console.WriteLine();
                Console.WriteLine("----------------------------------------------------------------------------------");
            }
            if (i <= 53)
            {
                //Console.Write(i + ": ");
                if ((int)line[i] == 65533)
                {
                    Console.Write("0 ");
                }
                if ((int)line[i] != 65533)
                {
                    Console.Write((int)line[i] + " ");
                }
            }
            
            if (i>53)
            {
                if((int)line[i] < 10)
                {
                    Console.Write(" ");
                }
                Console.Write((int)line[i + 0]);
                Console.Write(" ");
                if ((int)line[i+2] < 10)
                {
                    Console.Write(" ");
                }
                Console.Write((int)line[i + 2]);
                Console.Write("   ");
                if ((i + 1) % 3 == 0)
                {
                    Console.WriteLine();
                }
                i = i + 2;
            }
        }
    }
    sr.Close();
    Console.ReadLine();
}
catch(Exception e)
{
    Console.WriteLine("Exception: " + e.Message);
}
finally
{
    Console.WriteLine("Executing \"finally\" block.");
}

Answer 1

Okay so I just tried your code with a white bmp image of size 339x103 and this is what I got:

Header
        Signature: 66 77
        File size: 0 69 0 0
        Reserved: 0 0 0 0
        Data offset: 118 0 0 0

Info header:
        Header size: 40 0 0 0
        Image width: 83 1 0 0
        Image height: 103 0 0 0
        Number of color planes: 1 0
        Bits per pixel: 4 0
        Compression: 0 0 0 0
        Image size: 52 69 0 0
        X resolution: 0 0 0 0
        Y resolution: 0 0 0 0
        Pixels per meter: 0 0 0 0
        Number of colors: 0 0 0 0 

Considering the fact that " All of the integer values are stored in little-endian format (ie least-significant byte first) ", that line:

        Image width: 83 1 0 0

should be read: 83 + 1*256 + 0*256^2 + 0*256^3 = 339 which is the expected width...

However, there is indeed a problem when byte value is between 128 and 255, because then (int)line[i] will resolve to 65533. I suggest reading bytes from file instead of lines, in order to get rid of this problem. See File.ReadAllBytes