[Bug 1797875] [NEW] ImageMagick 8:6.8.9.9-7ubuntu5.13 quality regression

[Jeroen]

Public bug reported:

I would like to report a regression in ImageMagick
8:6.8.9.9-7ubuntu5.13. This report is related to
https://bugs.launchpad.net/bugs/1796563, but involves image quality
instead of permissions.

What happens:  In the new version (= security patch) of ImageMagick, the
quality of converted images is in some cases lower compared to the old
version. It is not visible on all converted images, some seem to suffer
more than others. In our case, converting postal barcodes from PDF to
PNG results in unscannable codes. The release information for the new
version does not mention any impact on quality.

Versions involved:

- OS: Ubuntu 16.04.4 LTS
- Imagemagick: 8:6.8.9.9-7ubuntu5.13 (suffering this issue)
- Imagemagick: 8:6.8.9.9-7ubuntu5.12 (working properly)

# convert --version
Version: ImageMagick 6.8.9-9 Q16 x86_64 2018-09-28 http://www.imagemagick.org
# convert demo.pdf demo_new.png

# convert --version
Version: ImageMagick 6.8.9-9 Q16 x86_64 2018-07-10 http://www.imagemagick.org
# convert demo.pdf demo_old.png

Attached a few sample images;
- On the demo_[old|new].png, note the text in the yellow area
- The eventbrite images are screenshots of a part of the converted
PNG, due to privacy protection.

** Affects: imagemagick (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: convert image imagemagick quality regression

** Attachment added: "Sample images"
   https://bugs.launchpad.net/bugs/1797875/+attachment/5201212/+files/images.tar.gz

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https://bugs.launchpad.net/bugs/1797875

Title:
  ImageMagick 8:6.8.9.9-7ubuntu5.13 quality regression

Status in imagemagick package in Ubuntu:
  New

Bug description:
  I would like to report a regression in ImageMagick
  8:6.8.9.9-7ubuntu5.13. This report is related to
  https://bugs.launchpad.net/bugs/1796563, but involves image quality
  instead of permissions.

  What happens:  In the new version (= security patch) of ImageMagick,
  the quality of converted images is in some cases lower compared to the
  old version. It is not visible on all converted images, some seem to
  suffer more than others. In our case, converting postal barcodes from
  PDF to PNG results in unscannable codes. The release information for
  the new version does not mention any impact on quality.

  Versions involved:

  - OS: Ubuntu 16.04.4 LTS
  - Imagemagick: 8:6.8.9.9-7ubuntu5.13 (suffering this issue)
  - Imagemagick: 8:6.8.9.9-7ubuntu5.12 (working properly)

  # convert --version
  Version: ImageMagick 6.8.9-9 Q16 x86_64 2018-09-28 http://www.imagemagick.org
  # convert demo.pdf demo_new.png

  # convert --version
  Version: ImageMagick 6.8.9-9 Q16 x86_64 2018-07-10 http://www.imagemagick.org
  # convert demo.pdf demo_old.png

  Attached a few sample images;
  - On the demo_[old|new].png, note the text in the yellow area
  - The eventbrite images are screenshots of a part of the converted
  PNG, due to privacy protection.

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