amandaghassaei/golden_angle_animation.md

## golden_angle_animation.md

      
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    Golden Angle Animation using ffmpeg

Update: I've turned this into a web app!
This is a single line command to generate a "golden angle" animation by rotating an image in increments of 137.5 degrees.  Try this out on images of pinecones, succulents, flowers, fruits, and vegetables – anything that exhibits fibonacci spirals. I'll post some examples in the comments below.
I came across this idea while reading about the artist John Edmark, who creates hypnotizing zoetrope sculptures.  He said in an interview that you could take a pineapple or pinecone and put it on a turntable with a strobe light for the same effect, and I wanted to test it out.
Steps To Use:

Install ffmpeg and run the following command:
FILE="image.jpg"; CENTER_X="1000"; CENTER_Y="1000"; ffmpeg -loop 1 -i $FILE -r 10 -vframes 157 -filter_complex "crop=min(iw-2*abs(iw/2-$CENTER_X)\,ih-2*abs(ih/2-$CENTER_Y)):out_w:$CENTER_X-out_w/2:$CENTER_Y-out_h/2" -c:v libx264 -preset slow -crf 22 -pix_fmt yuv420p -an "${FILE%.*}_golden_tmp.mp4"; ffmpeg -i "${FILE%.*}_golden_tmp.mp4" -filter_complex "rotate=a=n*2.4:c=black:ow=trunc(1/sqrt(2)*iw/2)*2:oh=ow" -c:v libx264 -preset slow -crf 22 -pix_fmt yuv420p -an "${FILE%.*}_golden.mp4"; rm "${FILE%.*}_golden_tmp.mp4"
At the beginning of the line:

Set FILE to your image (can be any image format).
Set CENTER_X and CENTER_Y to the x and y position to rotate around (measured in pixels with (0, 0) at the top left corner of the image).  For a perfectly centered image CENTER_X is width / 2 and CENTER_Y is height / 2.  I use the ruler tool in Photoshop to measure the location of the center point.

More Info:


-loop 1 -r 10 -vframes 157 creates a video from the image with a framerate of 10 frames per second and a total 157 frames.  157 is a good number to use because 157 * 2.4 radians / 6.28 radians = 60 rotations (this will give you a perfectly looping video).
-filter_complex "crop=min(iw-2*abs(iw/2-$CENTER_X)\,ih-2*abs(ih/2-$CENTER_Y)):out_w:$CENTER_X-out_w/2:$CENTER_Y-out_h/2" crops the video to a square, centered around the desired center point.
-filter_complex "rotate=a=n*2.4:c=black:ow=trunc(1/sqrt(2)*iw/2)*2:oh=ow" rotates each frame of the video by 2.4 radians (137.5 degrees) and crops to a tight fit for all rotated frames.  There is some extra code in there to ensure that the resulting width and height of the output video are divisible by 2 (required for mp4).  You might also try a=-n*2.4 to rotate the frames in the opposite direction.  I think some plants have other special angles, but I'm still figuring that out...  let me know in the comments if you find something!
-c:v libx264 -preset slow -crf 22 encodes as h.264 with better compression settings.
-pix_fmt yuv420p makes the mp4 compatible with web browsers.
-an creates a video with no audio.
rm "${FILE%.*}_golden_tmp.mp4" removes a temp file created in this process.  I would like to avoid temp files, but found that ffmpeg has some kind of bug that was causing duplicated frames or inconsistent rotation between frames when I ran this as a single command.  Let me know in the comments if you know a better way.