Why do BITMAPS load “upwards”?

Question

If you have a really really large JPG and a BMP embedded on HTML and you load it into Firefox, you will notice that the JPG will load \"downwards\" (paint from left to right, th

Answer 1

Bitmap coordinates start at the bottom left of the screen - this makes perfect sense if you think of a graph, you start the origin at the lower left.

Most graphics devices start at the top left - because raster scanning displays like CRTs started the scan at the top (why?) and LCDs continued the standard

Answer 2

I wrote a bitmap parser a while back, and if I remember correctly, bitmaps store the image backwards. That is, it stores the lower rows first and the higher rows last. The data arrives to your browser in-order, so that's why you can watch it load from the bottom up.

EDIT: Here's a better link that pretty much tells you everything you would ever want to know about a bitmap file: http://en.wikipedia.org/wiki/BMP_file_format