JOSM adds blur to aerial imagery?

[dieterdreist]

This is nothing new but something I am experiencing for many years now. JOSM seems to blur the imagery on high zoomlevels. I am not sure it happens with every source (e.g. Bing does not seem so, but then they are blurry around here anyway, so I am not sure).
It seems to happen with mapbox imagery. Please look at the attached screenshots which show the unblurred and blurred layer.
Or maybe it is something that mapbox does upstream?

PS: It may not be completely evident from looking at the screenshots, but if you compare the smaller zoomlevel in 200% viewing size to the higher zoomlevel at 100% (i.e. same real life scale) it becomes very clear the there is some blurring going on, the 200% scaled zoom is much sharper than the 100% 1:1 screenshot.

[dieterdreist]

comparison of 100% screenshot with a screenshot of a smaller scale in 200% with no fancy interpolation

[dieterdreist]

I have now added a third screenshot (comparison) to make it easy to see. The 200% was made without interpolation (no lanczos, cubic or similar).

[Klumbumbus]

The interpolation comes from mapbox. They deliver tiles on higher zoom levels interpolated from lower zoom levels if no higher zoom levels are available.
The problem is that such global sources as mapbox have different ("true") maximum zoom levels depending on the area.
If you only edit in one area you can adjust the max zoom in the imagery preferences. Then JOSM enlarges the tiles from the max zoom level, resulting in a sharp pixelated display.

General solutions could be:

• mapbox disables interpolation on the higher zoom levels
• mapbox delivers no tiles if no tiles are available at that zoom level
• mapbox delivers "dummy tiles" if no tiles are available at that zoom level (they did in the past) JOSM can detect these and instead display enlarged tiles from lower zoom

[dieterdreist]

Thank you for taking the time to respond. I have created a question in the mapbox forum on stackoverflow for this issue:
​https://stackoverflow.com/questions/62715967/refrain-from-blurring-aerial-imagery-high-zoom-images

[Klumbumbus]

Please reopen if someone knows a way to improve this from the JOSM side.

[stoecker]

One option missing: A specific header is delivered stating what happens. JOSM imagery can interpret these headers as "empty tile" info.

[Klumbumbus]

Thats what I meant with my 3rd point. Currently we have
<no-tile-header name='ETag' value='"067736a547cafe90014b4e59b6510abe"|"ee1f6802b0234046b553cbbc672ac7d9"|"9f5a2f1d7cc131e58befc2052c71c827"' />

[anonymous]

Can you share osm link of this location?

Replying to dieterdreist:

This is nothing new but something I am experiencing for many years now. JOSM seems to blur the imagery on high zoomlevels. I am not sure it happens with every source (e.g. Bing does not seem so, but then they are blurry around here anyway, so I am not sure).
It seems to happen with mapbox imagery. Please look at the attached screenshots which show the unblurred and blurred layer.
Or maybe it is something that mapbox does upstream?

PS: It may not be completely evident from looking at the screenshots, but if you compare the smaller zoomlevel in 200% viewing size to the higher zoomlevel at 100% (i.e. same real life scale) it becomes very clear the there is some blurring going on, the 200% scaled zoom is much sharper than the 100% 1:1 screenshot.

[dieterdreist]

Sorry for replying after some days. The specific situation of the screenshot is around here: ​https://www.openstreetmap.org/way/161529140#map=18/42.21914/12.40259
but it happens everywhere, it is a general problem. Zoom too much in mapbox aerial imagery in JOSM and it gets blurred.

[dieterdreist]

@josm team: I have reported this to mapbox and they wrote they will follow up here.

It's ... from Mapbox Support, happy to help!

Thank you for writing in and linking to your previous question on JOSM. A member of our Imagery team will follow up with you there. 

I hope this was helpful!