Jpegloop

Counting up

for ((i=1;i<=100;i++))
do
echo $i
done

Counting down

for ((i=1;i<=100;i++))
do
echo $i
done

Doing something

for ((i=1;i<=10;i++))
do
convert original.jpg -quality $i output$i.jpg
done

Fixing the filenames (zero padding with printf)

printf can be used to "zero-pad" a number (ie make a good filename from a counting number)

printf "%03d" 7

means "zero-pad" (add zeros) to always be 3 characters long, and outputs:

command substitution

$() means "command substitution" -- or do what's inside the parentheses and then substitute the result. This can be used to store the result of running printf in a variable (to then use again)

for ((i=1;i<=10;i++))
do
name=$(printf "%03d\n" $i)
convert original.jpg -quality $i output$name.jpg
done

Compressing the "lastframe" to perform an iterative compression

The trick here is to keep a "lastframe" copy that can always be used as the input to the convert command.

cp $j lastframe.jpg

for ((i=100;i>=1;i--))
do

name=$(printf "%03d\n" $((100-i)))
convert lastframe.jpg -quality $i output$name.jpg
cp output$name.jpg lastframe.jpg

done

ffmpeg -f image2 -i output%03d.jpg -r 10 $j.mp4

Converting the images to a movie

   ffmpeg -f image2 -i output%03d.jpg -r 10 output.mp4

Apply to a directory of files

The whole thing can be wrapped in a "for" loop to process a whole bunch of input images at once.

#!/bin/bash

for j
do
    cp $j lastframe.jpg

    for ((i=100;i>=1;i--))
    do

        name=$(printf "%03d\n" $((100-i)))
        convert lastframe.jpg -quality $i output$name.jpg
        # COPY THE CURRENT TO "lastframe.jpg"
        cp output$name.jpg lastframe.jpg
    
    done
    ffmpeg -f image2 -i output%03d.jpg -r 10 $j.mp4

done