Text that stays readable while things move
The background under a caption changes on every frame, so a plain white line that reads perfectly at the start can vanish two seconds in. An outline or a shadow behind the text solves it in one step, which is why captioned GIFs almost always use one.
Position matters too: the top and bottom edges are usually calmer than the middle, and they are where a viewer expects a caption to be.
Captioning part of an animation
Applying text to a frame range rather than the whole GIF gives you crude subtitles — one line while something happens, another line afterwards. It costs nothing in file size, since GIF frames are stored independently anyway.
What it does to the file
Very little. Text is flat, hard-edged and made of few colours, which is exactly what GIF compresses well. A caption typically adds a couple of per cent — unlike anything photographic, which fights the 256-colour palette.
Frequently asked questions
Why does my caption disappear partway through?
The background moved under it. Use the outline or shadow so the text reads against light and dark alike, and keep captions near the top or bottom edge.
Can I put different text on different parts?
Yes — apply text to a range of frames rather than all of them, and repeat for the next range. That gives you simple subtitles.
Will it make the file much bigger?
No. Flat text with hard edges is the kind of content GIF handles best; expect a couple of per cent at most.
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