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Tag: imagemagick

ImageMagick, four point perspective distortion in a video

Step 1) Download the video from Youtube using JDownloader. The best one was the original Japanese upload, The Game Awards 2014 出展映像 ゼルダの伝説 最新作, which is 720p. I saved this file as zelda_720p.mp4.

Step 2) Transform the video in a series of PNGs.

mplayer -nosound -vo png:z=9 zelda_720p.mp4

This generated image files ranging from 00000001.png to 00007563.png.

Step 3)
Using Gimp, find the 2 sets of 4 points for the perspective. The first in red is the source and the one in blue is the destination.

zelda video four point perspective

Step 4) Apply ImageMagick’s four point perspective distortion in each image using a ShellScript.

#!/bin/sh
for image in *.png;
do
  convert $image -matte -virtual-pixel transparent \
  -distort Perspective \
  '60,90 0,0 50,415 0,720 582,418 1280,720 589,147 1280,0' \
  p_$image
done

Now I have images in the format p_00000001.png to p_00007563.png. Because PNG is a lossless format, the perspective lost less information in this step than it would if step 2 was outputting jpgs.

Step 5) Convert frames to jpgs using ImageMagick and ShellScript.

#!/bin/sh
for image in p_*.png;
do
  convert $image "${image/.png/}.jpg"
done

Where “${image/.png/}.jpg” removes the .png in the image string.

Ps: this step is not really necessary as you could use png as input to ffmpeg.

Step 6) Convert jpgs in a video.

ffmpeg -start_number 0 -i '%08d.jpg' -c:v libx264 output.mp4

‘%08d.jpg’ means a 8 digits filled with zeros in the left followed by .jpg, in this case 00000001.jpg to 00007563.jpg.

With this, I have the output.mp4 video ready to upload.

The whole process took several hours and a total 13GiB, although the final video has only 96 MiB. This could be optimized using pipelines and parallelism if it was needed to repeat the process.

HackerNews discussion: https://news.ycombinator.com/item?id=8713070

PNG to PDF and PNG to PDF

You can use ImageMagick to convert multiple PNGs into a PDF and convert a multiple pages PDF into multiple PNGs.

PDF to PNG

$ convert document.pdf document.png

For a document with 10 pages, this will generate document-0.png, document-1.png, … document-9.png.

PNG to PDF

$ convert document*.png document.pdf

This convert the PNG pages into pages in the document.pdf document.

Creating a lot of thumbnails with Shell script

This script create a thumbnail with width 100 of each png file in the actual directory.

#!/bin/sh
for i in *.png
do
	echo "convert -thumbnail 100 $i $i"
	convert -thumbnail 100 $i $i
done