Bitmap Stride And 4 bytes Relation?

Question

Whats does this sentence mean:

The Stride property, holds the width of one row in bytes. The size of a row however may not be an exact multiple of the pix

Answer 1

Stride is padded. That means that it gets rounded up to the nearest multiple of 4. (assuming 8 bit gray, or 8 bits per pixel):

Width | stride
--------------
1     | 4
2     | 4
3     | 4
4     | 4
5     | 8
6     | 8
7     | 8
8     | 8
9     | 12
10    | 12
11    | 12
12    | 12

etc.

In C#, you might implement this like this:

static int PaddedRowWidth(int bitsPerPixel, int w, int padToNBytes) 
{
    if (padToNBytes == 0)
        throw new ArgumentOutOfRangeException("padToNBytes", "pad value must be greater than 0.");
    int padBits = 8* padToNBytes;
    return ((w * bitsPerPixel + (padBits-1)) / padBits) * padToNBytes;
}

static int RowStride(int bitsPerPixel, int width) { return PaddedRowWidth(bitsPerPixel, width, 4); }