How to overlay and repeat non-animated image over an animated one?

[slnc]

I have two gifs: aura.gif which is a 7 frames animation, and character.gif which is a 1 frame image. When I overlay one on top of the other as shown below, I get a 7 frames animated image but the character in character.gif only appears in the first frame.

How can I make character.gif "appear" in all frames of aura.gif when I overlay both images?

This is the code I'm currently using:

require 'vips'

character = File.open("character.gif").read
character_b = Vips::Image.new_from_buffer(character, "", access: 'sequential', n: -1)

aura = File.open("aura.gif").read
aura_b = Vips::Image.new_from_buffer(aura, "", access: 'sequential', n: -1)

aura_b.composite(character_b, "over", x: 0, y: 0).webpsave("composite.gif")

Thanks

[slnc]

After digging around a bit more I realized that Vips models animated images as a huge image so I ended up with this code which does what I need:

require 'vips'

character = File.open("character.webp").read
character_b = Vips::Image.new_from_buffer(character, "")

aura = File.open("aura.webp").read
aura_b = Vips::Image.new_from_buffer(aura, "", access: 'sequential', n: -1)

page_h = aura_b.get("height") / aura_b.get("n-pages")
aura_b.get("n-pages").times.each do |i|
  aura_b = aura_b.composite(character_b, "over", x: 0, y: page_h * i)
end

aura_b.webpsave("composite.webp")

[jcupitt]

Hi @slnc,

That'll work, but it'll be pretty slow since every pixel will need to pass through a stack of n_pages composite operations. A quicker solution would be to copy the character n_pages times vertically, then do a single composite for the whole animation.

replicate tiles images:

https://www.rubydoc.info/gems/ruby-vips/Vips/Image#replicate-instance_method

It's extremely quick (it just copies pointers), so you can use it instead of any kind of loop over the X and Y dimensions.

Something like:

require 'vips'

character = Vips::Image.new_from_file(ARGV[0])
aura = Vips::Image.new_from_file(ARGV[1], access: 'sequential')

character = character
    .replicate(1, aura.get("n-pages"))
aura
    .composite(character, "over")
    .write_to_file(ARGV[2])

Then:

$ ./x.rb ~/pics/character.gif ~/pics/aura.gif[n=-1] x.gif

To make:

[slnc]

Thanks a lot John!

[jcupitt]

Argh! Please don't cross post questions. It makes extra unnecessary work for volunteer maintainers.

[slnc]

I'm sorry, I checked activity on both SO for tag "vips" and on this forum before posting. I posted on both places because I got the impression that neither had a lot of activity. I realize now that SO has quite a bit of activity and that my assumption that if I got an answer on both places it would be better because a question and a solution would appear on two places instead of one.

Perhaps consider making this request (to not cross-post) a bit more visible with maybe a "How to get help" section and a message like "If you need help go here or here but don't cross post" either on https://www.libvips.org/ or https://github.com/libvips/libvips? I easily spent 1h browsing those two sites but if that section exists, I missed it. Just a suggestion to help other people who might be tempted to do like I did. :-)

Again, thank you for your help John. 🙏

[jcupitt]

It's a general rule with all active open source projects: ask once, and only ask around if you don't get a reply. libvips is an evenings and weekends thing, and it'd obviously be much more fun to work on adding something new than answering the same question several times.

[slnc]

I understand, I will follow your directions next time.

Thanks again for your help, the code you helped me with is already in production. :-)