Why must “stride” in the System.Drawing.Bitmap constructor be a multiple of 4?

Question

I am writing an application that requires me to take a proprietary bitmap format (an MVTec Halcon HImage) and convert it into a System.Drawing.Bitmap in C#.

The only

Answer 1

As has been stated before by Jake you calculate the stride by finding the bytes per pixel (2 for 16 bit, 4 for 32 bit) and then multiplying it by the width. So if you have a width of 111 and a 32 bit image you would have 444 which is a multiple of 4.

However, let's say for a minute that you have a 24 bit image. 24 bit is equal to 3 bytes, so with a 111 pixel width you would have 333 as your stride. This is, obviously, not a multiple of 4. So you would want to round up to 336 (the next highest multiple of 4). Even though you have a bit of extra, this unused space is not significant enough to really make much of a difference in most applications.

Unfortunately, there is no way around this restriction (unless you always use 32 bit or 64 bit imagines, which are always multiples of 4.