Crop for animated images

[Mefgalm]

Hello! Thanks for this great library!

I have .gif and .webp files, on which I try to apply Image.thumbnail(image, dims, crop: center) which leads to the animation disappearing. When opening images I pass pages: -1. Resizing animated images works correctly.

Perhaps libvips itself does not currently support this option: libvips/libvips#2668

[kipcole9]

I believe you are correct in that libvips doesn't support thumbnailing/cropping animated images.

I think I might be able to do this for webp simple animated images (ones that don't have the ANIM chunk and just have simple loop and delay headers) by splitting the image, cropping each frame and reassembling.

I'll do some experiments today on this. If webp works well enough I'll take a look at gif.

[kipcole9]

Well that was fun! I've pushed a commit that adds Image.map_pages/2 that will execute a function for each page in an image, then reassemble into a new image and set the page height correctly. I've got a simple doctest for an animated .webp image that appears to work as follows:

# This image is included in the image repo, please adjust the path to suit in your
# environment
iex> image = Image.open!("./test/support/images/animated.webp", pages: -1)
iex> {:ok, mapped_image} = Image.map_pages(image, &Image.crop(&1, 0, 200, 200, 200))
iex> Image.write(mapped_image, "/path/to/some_place/image.webp")

If you then view the image in your browser I believe you will see a an animated cropped image.

When I'm comfortable its all working as expected - and potentially test on a .gif animated file, I'll make this a standard part of Image.crop/5 and Image.thumbnail/3.

Would you consider trying this out and give me your feedback? Just configure image in mix.exs as {:image, github: "kipcole9/image} followed by mix deps.get.

[kipcole9]

I've added a test for animate GIF images - these also seem to work.

[kipcole9]

I've published image version 0.38.0 with the following changelog. You'll see the new function Image.map_pages/2 and that Image.crop/5 will now correctly process multi-page images (like animated '.wepband.gif` images). Thanks for the motivation to get this done.

Bug Fixes

• Fix extend_mode: :black color handling for images with an alpha band. Also fixes when the image is a single band image. Thanks to @icefoxen for reporting the issue. Closes Image.embed does mysterious things with transparent images #108.

Enhancements

• Adds a squircle mask function and a squircle avatar shape option. Thanks to @gf3 for the PR.

• Adds Image.map_pages/2 to execute a function for each page in a .webp or .gif image then reassemble the pages into a new image. This can be used to crop all the frames of an animated image. Thanks to @Mefgalm for the prompt to get this done. Eventually this function will be used by default for Image.crop/5 and Image.thumnail/3.

• Adds Image.pages/1 to return the number of pages in an image. For normal images the result will be 1. For animated images it will be the number of frames in the animation.

• Adds support for cropping multi-page images (like animated .webp and .gif images) in Image.crop/5.

• Adds Image.Shape.circle/2, Image.Shape.ellipse/3 and Image.Shape.line/5 as well as their ! counterparts.

• Allow pages: :all as a synonym for pages: -1 when opening an image.