Preview is blurry for large PNG files

[JoKalliauer]

For large (large high) PNGs the Preview of the Croptool is quite blurry

File is from https://commons.wikimedia.org/wiki/File:Python_-data-project-shared-pywikibot-core-generate_user_files-py.png#filehistory

Transfered bug from https://phabricator.wikimedia.org/T219820

[danmichaelo]

Just the preview or the end result as well?

[JoKalliauer]

@danmichaelo :

Just the preview. (I change the description.)

The result is lossless https://commons.wikimedia.org/wiki/File:Python_-data-project-shared-pywikibot-core-generate_user_files-py.png#filehistory

I wanted a pixel-precise cut, since I wanted delete some textlines, but still keep some black margin.

[danmichaelo]

Thanks for clarifying. Yes, I agree that Croptool could be improved to better support pixel-perfect cropping. Perhaps it would help to double the thmbnail size and scale it down, esp. on HiDPI monitors and when zooming. Talking about the zoom, it would be nice if the selection didn't change when zooming, but it's a feature of cropper.js I haven't figured out how to fix yet.