Adding Labels Using Imagemagick

Years ago I wanted to edit a video clip, add a label, and make a gif. I wrote about it in this gist. I’m revisiting it now and posting it for discoverability. Surprisingly, I can still understand what I wanted to do!

This was to add “hello world” label onto the gif, while slowing it down in the moment. It was used for a blooper shot, so the slowdown was more dramatic effect and annotated as such.

Anyhoo, here’s the original post.

---

Summary

Imagemagick is hard to use and the documentation/tutorials available are not intuitive. Here is a concise explanation of what needs to be done to edit a gif to add labels.

Code

convert foo.gif \                                                            # Specify the original gif
-gravity center -pointsize 30 -font ComicSans \                              # Set font position and styling
-duplicate 1,0-20 \                                                          # Clone frames and append to the end (clone frame once)
'(' -clone 21-40 -fill white -annotate -0-150 'Hello' -set delay 6 ')' \     # Clone frames, add 'Hello', and slow down gif delay for only these frames
-duplicate 1,41-89 \                                                         # Clone frames and append to the end (clone frame once)
'(' -clone 90-120 -fill white -annotate -60-50 'World' -set delay 4 ')' \    # Clone frames, add 'World', and set delay
-delete 0-120 \                                                              # Delete the original frames
foo_output.gif                                                               # Output file

Notes

• convert is the imagemagick command that is used to modify gifs
• -gravity is used to set the position of the text. This is what x y offsets are relative to
• frames are either duplicated or cloned+modified, appending them to the existing gif and control ordering. -delete is used to remove the original frames
• -duplicate will copy the frame range and append to the end. This is memory-efficient way to clone frames (imagemagick only copies reference frame upon write) but doesn’t allow modification
• -clone requires imagemagick’s parenthesis scope. Modified frames are appended to the end

Reference

convert reference

Frame-by-frame modification