I have created a document which has a single column section at the beginning of the first page, and two columns sections thereafter. I have noticed that when I insert picture into column 1, and expand its size to cover both columns, two column layout behaves appropriately. However, how can I insert single column picture description (centered text) now, without braking the float in underneath two column layout?
If you want to change from two-columns to a single column layout at the end of the two-column section, refer my answer here. If you want to exit a two-column layout somewhere in the middle you will have to use a more tedious manual method of returning the content to single column layout, then re-marking the required fore and aft sections as two-column again (allow some content in the middle that is single column).
The answer is - by using caption