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Stop using the PNG format for HEIC thumbnails #41284
Description
Steps to reproduce
- enable preview for HEIC files (use the latest Imagick, install php-imagick and enable preview in the config, enabled by default)
- upload a HEIC file (photo)
- access this file via your web browser
- its preview(s) is (are) generated, in the PNG (!) format
Expected behaviour
The preview image(s) should not be created in the PNG format, since this format is not usable for photos at all. In my case, the preview files occupy even more space than the original, large photos themselves (20 GB vs. 19 GB). It seems to me that the e.g. the JPG format would be much more suitable.
Actual behaviour
Thumbnails of any HEIC file/photo are generated in the PNG format.
Note: The reason is that the HEIC.php file that generates these thumbnails extends the Bitmap class which uses only the PNG format and cannot be configured to any other file type easily.
Thank you.
Activity
iasdeoupxe commentedon Nov 30, 2024
Could be wrong but looks like all image types (not only HEIC) are getting thumbnails in the .png format, at least noticed .jpg files on my installation.
github-actions commentedon May 30, 2025
This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 10 days if no further activity occurs. Thank you for your contributions.
tmysik commentedon May 30, 2025
Still valid, no change here.
@DeepDiver1975 IMHO, this can hardly be an enhancement - try to have 1 GB of HEIC images and let OwnCloud generate 1.5 or 2 GB thumbnails. That does not make any sense at all.
cortho commentedon Jul 25, 2025
I strongly second @tmysik when thumbnails go into 5 Megabytes or more this is clearly no enhancement but a bug.
DeepDiver1975 commentedon Jul 25, 2025
Contributions welcome! THX
github-actions commentedon Jan 22, 2026
This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 10 days if no further activity occurs. Thank you for your contributions.
tmysik commentedon Jan 22, 2026
@DeepDiver1975 just curious - why did you mark this ticket as enhancement?
DeepDiver1975 commentedon Jun 24, 2026
🤖 Automated issue triage by Claude Code review agent.
Confirmed and root-caused on current
master.Root cause. HEIC previews are produced by
lib/private/Preview/Heic.php, which extendsOC\Preview\Bitmap.Bitmap::getResizedPreview()hardcodes the output format:There is no configuration hook to choose a different container, so every Bitmap-derived provider (HEIC, and the other formats routed through
Bitmap) always emits PNG. For photographic content this is exactly the wrong choice: PNG is lossless and the resulting previews can be larger than the lossy source — matching the reports here of thumbnail directories rivaling or exceeding the size of the original HEIC library (≈20 GB of previews for ≈19 GB of photos, multi-MB single thumbnails). The size blow-up is a real defect of the preview subsystem, not merely a stylistic format preference.Suggested direction for a fix. Emit a lossy format for photographic previews — e.g.
setImageFormat('jpeg')with a sanesetImageCompressionQuality()(commonly ~80–85), ideally configurable, while keeping PNG where transparency matters. Note the comment from @iasdeoupxe that non-HEIC images (e.g. JPEG sources) also appear to receive PNG previews, consistent with the sharedBitmapcode path above.This triage does not change the issue's labelling and posts no code change. As @DeepDiver1975 noted, contributions are welcome; the affected line is
lib/private/Preview/Bitmap.php:104.dj4oC commentedon Jul 8, 2026
Implementation prompt
Problem:
OC\Preview\Bitmap::getResizedPreview()hardcodes$bp->setImageFormat('png')for every Bitmap-derived preview provider (HEIC and others), so photographic previews are always lossless PNG and can end up larger than the original lossy source image (reported: ~20GB of previews for ~19GB of HEIC photos).Acceptance criteria:
OC\Preview\Bitmapfor photographic bitmap sources use a lossy output format (e.g. JPEG) with a configurable compression quality, measurably reducing preview size versus current PNG output on representative HEIC/JPEG fixtures.preview_*config keys, with a sane default.Files:
lib/private/Preview/Bitmap.php—getResizedPreview()($bp->setImageFormat('png')) andresize(); add a format/quality decision (setImageFormat('jpeg')+setImageCompressionQuality()), gated by new config.Constraints:
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