`Vips::Image#height` of thumbnail_image is different in Ubuntu 22.04

[yahonda]

Describe the bug
Vips::Image#height of thumbnail_image is different in Ubuntu 22.04

To Reproduce

1. Install Ruby 3.3.0 on Ubuntu 22.04

$ ruby -v
ruby 3.3.0 (2023-12-25 revision 5124f9ac75) [aarch64-linux]

2. Install the latest ruby-vips

$ gem install ruby-vips

3. Download the webp file

$ wget https://raw.githubusercontent.com/rails/rails/main/activestorage/test/fixtures/files/valley.webp

4. Save this file as thumbnail_height.rb

require 'vips'

# Load the input image
input_image = Vips::Image.new_from_file('valley.webp')

# Define the thumbnail width and height
thumbnail_width = 50
thumbnail_height = 50

# Create the thumbnail image
thumbnail_image = input_image.thumbnail_image(thumbnail_width, height: thumbnail_height)
p thumbnail_image.height

5. Run ruby thumbnail_height.rb

$ ruby thumbnail_height.rb

6. It returns 34 as the height of the thumbnail

$ ruby thumbnail_height.rb
34

Expected behavior
It should show 33

Screenshots
If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• OS: Ubuntu 22.04.3 LTS
• Browser wget is only used to download the test file.
• Version GNU Wget 1.21.2 built on linux-gnu.

Additional context
This issue is opened while investigating Rails CI isssue
https://buildkite.com/rails/rails-nightly/builds/149#018d9052-1b2d-48fa-9d74-a39df3f3f1d6/1251-1291
It had been working fine, that means the height of the thumbnail had been 33.

I attempt to reproduce this issue using libvips42 only but it does not reproduce.

• Steps without ruby-vips

$ vipsthumbnail valley.webp -s 50x50
$ identify -format "%h" tn_valley.jpg
33

• Installed apt packages

$ apt list --installed | grep libvips

WARNING: apt does not have a stable CLI interface. Use with caution in scripts.

libvips-doc/jammy,now 8.12.1-1build1 all [installed,automatic]
libvips-tools/jammy,now 8.12.1-1build1 arm64 [installed]
libvips42/jammy,now 8.12.1-1build1 arm64 [installed]

[jcupitt]

Hello @yahonda,

I would guess you are seeing results from two different libvips versions -- there have been some improvements to the rounding behaviour of thumbnail.

This is off-topic, but I would not use thumbnail_image, it's only there for emergencies. You will find plain thumbnail is often much faster and uses a lot less memory. For example:

$ vipsheader nina.jpg
nina.jpg: 6048x4032 uchar, 3 bands, srgb, jpegload

I see:

$ /usr/bin/time -f %M:%e vips thumbnail_image nina.jpg x.jpg 100
218112:0.25
$ /usr/bin/time -f %M:%e vips thumbnail nina.jpg x.jpg 100
38556:0.06

thumbnail_image is 250ms and 220mb of memory, but thumbnail is 60ms and 38mb. In fact, it's better than that since the startup / shutdown cost for vips is included.

$ /usr/bin/time -f %M:%e vips > /dev/null
31232:0.02

So really it's 230ms and 190mb of memory versus 40ms and 7mb -- thumbnail is 6x faster and needs 30x less memory.

[yahonda]

Thanks for the update.

I would guess you are seeing results from two different libvips versions -- there have been some improvements to the rounding behaviour of thumbnail.

Thanks for the info. Here are the installed libvips42 version those height returns 33.

$ apt list --installed | grep libvips

WARNING: apt does not have a stable CLI interface. Use with caution in scripts.

libvips-dev/mantic,now 8.14.3-1 amd64 [installed]
libvips-tools/mantic,now 8.14.3-1 amd64 [installed]
libvips42/mantic,now 8.14.3-1 amd64 [installed]
$

Here are the installed libvips42 version those height returns 34.

$ apt list --installed | grep libvips

WARNING: apt does not have a stable CLI interface. Use with caution in scripts.

libvips-doc/jammy,now 8.12.1-1build1 all [installed,automatic]
libvips-tools/jammy,now 8.12.1-1build1 arm64 [installed]
libvips42/jammy,now 8.12.1-1build1 arm64 [installed]

This is off-topic, but I would not use thumbnail_image, it's only there for emergencies. You will find plain thumbnail is often much faster and uses a lot less memory. For example:

$ vips thumbnail valley.webp thumbnail.jpg 50 --height 50
$ identify -format "%h" thumbnail.jpg
33

I'm wondering why even the vips thumbnail creates the thumbnail whose height is 33 in command line while ruby-vips returns 34.

[yahonda]

I have opened rails/rails#51060 to allow both height, 33 and 34 at Rails CI.

[jcupitt]

I'm wondering why even the vips thumbnail creates the thumbnail whose height is 33 in command line while ruby-vips returns 34.

I think your ruby-vips and vips CLI must be using a different libvips versions.

[yahonda]

Thanks for the information. Understood.

I think your ruby-vips and vips CLI must be using a different libvips versions.

[kleisauke]

This was a bug that has been fixed in libvips 8.13 - see:
https://www.libvips.org/2022/05/28/What's-new-in-8.13.html#image-resize-quality-improvements

Resizing an 550×368 image to a width of 50 pixels should yield a height of 33 pixels.
$50 \div (550 \div 368) = 33.4545454545 \approx 33$

[yahonda]

This was a bug that has been fixed in libvips 8.13 - see:
https://www.libvips.org/2022/05/28/What's-new-in-8.13.html#image-resize-quality-improvements

That totally makes sense because libvips42/jammy,now 8.12.1-1build1 arm64 [installed] is installed. Thank for the useful information. Closing this issue.