Blend source and possibly others don't work properly

[tgrajewski]

Possible bug

Is this a possible bug in a feature of sharp, unrelated to installation?

• Running npm install sharp completes without error.
• Running node -e "require('sharp')" completes without error.

If you cannot confirm both of these, please open an installation issue instead.

Are you using the latest version of sharp?

• I am using the latest version of sharp as reported by npm view sharp dist-tags.latest.

If you cannot confirm this, please upgrade to the latest version and try again before opening an issue.

If you are using another package which depends on a version of sharp that is not the latest, please open an issue against that package instead.

What is the output of running npx envinfo --binaries --system --npmPackages=sharp --npmGlobalPackages=sharp?

  System:
    OS: Windows 11 10.0.26100
    CPU: (12) x64 Intel(R) Core(TM) i7-8700 CPU @ 3.20GHz
    Memory: 9.17 GB / 15.94 GB
  Binaries:
    Node: 22.13.1 - C:\Program Files\nodejs\node.EXE
    npm: 11.0.0 - C:\Program Files\nodejs\npm.CMD
  npmPackages:
    sharp: ^0.33.5 => 0.33.5

Does this problem relate to file caching?

The default behaviour of libvips is to cache input files, which can lead to EBUSY or EPERM errors on Windows.
Use sharp.cache(false) to switch this feature off.

• Adding sharp.cache(false) does not fix this problem.

Does this problem relate to images appearing to have been rotated by 90 degrees?

Images that contain EXIF Orientation metadata are not auto-oriented. By default, EXIF metadata is removed.

• To auto-orient pixel values use the parameter-less rotate() operation.

• To retain EXIF Orientation use keepExif().

• Using rotate() or keepExif() does not fix this problem.

What are the steps to reproduce?

Create background image in memory with Sharp. The image should have a solid background. Composite another image loaded from disk over the background gives wrong result for some blend modes, mainly source.

What is the expected behaviour?

Some blend modes (I haven't tested all of them), like source, completely erase background color, but only pixels in the area of the composited image should be affected.

Please provide a minimal, standalone code sample, without other dependencies, that demonstrates this problem

Simple composite over a solid pink background created in memory. This code should leave pink border around the image, as the background is bigger than the composited input image.

sharp({'create': {'width': 160, 'height': 147, 'channels': 4, 'background': '#ff00ff'}})
    .composite([{'input': './red.png', 'left': 5, 'top': 5, 'blend': 'source'}])
    .toFile('./result.png');

Please provide sample image(s) that help explain this problem

Composited input image red.png:

Expected result for the above example code:

Actual result file result.png (pink background is completely removed and it should be removed only under the composited image, leaving pink border):