Allow the user to select the JPEG save/compression quality

Authored by ngraham on Aug 12 2019, 4:27 AM.

Description

Allow the user to select the JPEG save/compression quality

Summary:
Currently, anytime Gwenview is used to save a non-JPEG file as a JPEG, or anytime JPEG file is saved or re-saved after performing a lossy edit (e.g. crop or red eye, but not rotation), the new file is saved with 75% quality level, resulting in a noticeable degradation in appearance.

This patch implements a user-selectable JPEG save/compression quality setting, which can be temporarily overridden in the Save As dialog when saving a file as a JPEG. The new default quality level is 90% -- same as Spectacle. This should prevent people from accdientally destroying their JPEGs.

As before, when saving an existing JPEG file with a new name or after performing a non-lossy edit (e.g. rotation, which only changes the EXIF rotation tag), the appearance of the file is not changed because no actual image manipulation is done.

FEATURE: 277996
FIXED-IN: 19.12.0

Test Plan:

Set JPEG quality to 5% in the config file and test the following use cases:

  • Non-JPEG image: do Save or Save As in non-JPEG formats -> No changes or regressions.
  • JPEG image: do Save or Save As without changing the image format or the image's pixels at all -> No changes; quality level not taken into consideration because these are lossless operations that do not re-compress the image (which is good)
  • JPEG image: do Save or Save As after changing the image's pixels in some way (e.g. a crop operation) -> Image is saved with the user-specified 5% quality level and looks terrible
  • JPEG image: do Save As into a non-JPEG file format after changing the image image's pixels in some way, or not -> No changes or regressions (in particular, lossless images like PNG are not hugely ballooned in file size)

Set JPEG quality to 90% in the config file and test the following use cases:

  • Non-JPEG image: do Save As in non-JPEG formats -> No changes or regressions; dialog box does not show quality spinbox
  • Non-JPEG image: do Save As into a JPEG and in the {nav Save As] dialog, change the quality from 90% to 5%-> Image is saved with the user-specified 5% quality level and looks terrible
  • JPEG image: do Save As into a non-JPEG file format -> No changes or regressions; dialog box does not show quality spinbox
  • JPEG image: do Save As after changing the image's pixels in some way (e.g. a crop operation), and in the {nav Save As] dialog, change the quality from 90% to 5%-> Image is saved with the user-specified 5% quality level and looks terrible

Reviewers: Gwenview, VDG

Subscribers: filipf, pino

Tags: Gwenview

Differential Revision: https://phabricator.kde.org/D23106

Details

Committed
ngrahamAug 24 2019, 5:37 PM
Differential Revision
D23106: Allow the user to select the JPEG save/compression quality
Parents
R260:3fdd733ef50c: Make it compile without foreach
Branches
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Tags
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