Interlaced effect on image with alpha using ffmpeg and some image editor like gimp

9. 8. 2019

In Gimp save first frame as bronto_001.png, reposition the logo and save as bronto_002.png.

Then, using ffmpeg

ffmpeg -i bronto_%03d.png -filter:v interlace bronto_interlaced.png

or, sharper

ffmpeg -i bronto_%03d.png -filter:v interlace=scan=1:lowpass=2 bronto_interlaced2.png

and with scale

ffmpeg -i bronto_%03d.png -filter:v scale=900:-1,interlace=scan=1:lowpass=2 bronto_interlaced_logo.png

Voila.

p.s. Css to embed this 1:1 ^

style="object-position: 0 0; object-fit: none; width:1313px; height:568px;"

p.s.2. The not-working-as-expected imagemagick way to interlace.

p.s.3. With imagemagick the gimp repositioning part could be simply done by adding transparent TL pixels on one and BR pixels on 2nd ‘field’. https://www.imagemagick.org/Usage/crop/#extent

Script ↓

#!/bin/bash

# InterlaceMagick (using imagemagick and ffmpeg)

# input should be transparent image 

# usage: interlaceMagick logo.png 0.5
#                                  ^ percents of height-based offset

set -ex

# input
logo="$1"
offset="$2"
[[ -z "$offset" ]] && offset="2"

# input breakdown 
file=$(readlink -f "$logo")       # quasi absolute
baseext=$(basename "${logo}")     # file.ext
base="${baseext%.*}"              # file
#ext="${file##*.}"                 # ext
dir=${file%/*}                    # directory

# tmp dir http://mywiki.wooledge.org/BashFAQ/062
tmp="/tmp/$RANDOM-$$"
trap '[ -n "$tmp" ] && rm -fr "$tmp"' EXIT
mkdir -m 700 "$tmp" || { echo '!! unable to create a tmpdir' >&2; tmp=; exit 1; }

# get logo height in px
height="$(convert "$1" -format "%h" info:)"
echo "$height px"

# now get N% of that height in px
n="$(convert xc: -format "%[fx:$height*$offset/100]" info:)"
echo "$n"

# field 1
convert "$file" -background transparent -splice "${n}"x"${n}" "$tmp/field_001.png"  

# field 2
convert "$file" -background transparent -gravity southeast -splice "${n}"x"${n}" "$tmp/field_002.png"

# interlace
ffmpeg -i "$tmp/field_%03d.png" -filter:v interlace=scan=1:lowpass=2 -y "$dir/${base}_interlaced.png"

3 pass degradation + some gimp video fx

Wallpapers ↓

video mine