Bird,
I'm no expert, so this is going to be an educated guess. I think the difference in the picture loading is in how the file was made. The jpeg files contain information that tells the viewer software where to "paint" the image. In the one type, the data is ordered line by line at the final resolution (detail level). In the other, the data is ordered every other, or third or fourth line. If its ordered every fourth line, it paints line 1, and duplicates line 1's data for line 2 and 3, then paints line 4, and duplicates line 4's data for lines 5 and 6, and continues until it reaches the bottom in this fashion. Now it goes to the top and fills in every fourth line starting with line 2, then returns to the top, fills in every fourth line starting with line 3 until it is done. THis takes 3 total passes, with more detail each pass, but a first pass that provides an "idea" of what the picture is going to look like before you wait around for the whole thing. Probably a throwback to the days of 12.4 Kbaud modems.
Just a guess, anyone else know better?
