JPEG - Idea and Practice/When the width or the height is not divisible by 8

In our program that produces the JPEG file, we have only used the largest part of the picture (beginning at the left top corner) which can be regularily divided up in 8x8-(or 16x16)-squares. If the dividing up does not fit the picture, the width or/and the height of the picture must be increased by the necessary number of pixels, and the new vertical and horizontal lines are usually coloured as the last vertical and horizontal line of the picture, respectively. The program that draws the picture from the file needs no changes: it draws in reality the extended picture, but we do only see the true part of it, because the drawing window is given the true width and height. The top picture (shown on an enlarged scale) has width and height of 33 pixels, and the width and the height must be increased by 7 pixels in order to be divisible by 8. If we extend the width and the height of the drawing window by 7 pixels, we will see the bottom picture: