First reported by @DavidLemayian. Comparison of the same PDF, one whose thumbnail was generated in February 2015, and one generated today:

But it's not a straight regression in image quality. The old downsampling looks better at thumbnail/small sizes, while the new looks better at normal/large. Click each ❌ or ✅ to view the image.
| Size | Old | New |
|---|
| Thumbnail | ✅ | ❌ |
| Small | ✅ | ❌ |
| Normal | ❌ | ✅ |
| Large | ❌ | ✅ |
First reported by @DavidLemayian. Comparison of the same PDF, one whose thumbnail was generated in February 2015, and one generated today:
But it's not a straight regression in image quality. The old downsampling looks better at thumbnail/small sizes, while the new looks better at normal/large. Click each ❌ or ✅ to view the image.