[Qgis-user] Disable anti-aliasing on XYZ layer

Tue Mar 14 21:54:09 PDT 2023

Thanks for the replies.

The imagery I'm working with comes from drone mapping.
The orthomosaic is generated using OpenDroneMap, in WGS84 UTM CRS
The resulting GeoTIFF is then re-projected  to Web-mercator 3857, before
being run through gdal2tiles.
At this stage I'm loading the tiles as an XYZ layer directly from my hard
drive, and my canvas is set at 3857 as well.
So I know that the two screenshots I attached earlier come from the same
PNG file.

When I set the zoom to 1:1 as suggested, I can see the PNG files are
displayed without anti-aliasing as expected.
But as soon as I zoom in further, anti-aliasing takes place to oversample
the image.
I have tried changing the parameters of the Resampling section in the Layer
Styling, but they have no effect at all (Zoomed In, Zoomed Out,
Oversampling and "Early re-sampling" options).

But the weirder thing is that when I set my XYZ layer source as
"Interpretation: MapTiler Terrain RGB", pixels are shown as squares when
over-zooming, like a standard raster would, which is what I want (even
though the data does not make any sense with the MapTiler Terrain RGB
styling, obviously).

Antialising does not help the interpretation of my imagery, and so far the
only solution I found was to create tiles up to zoom level 25, which is a
massive amount of overprocessing and storage, since level 21 is enough to
account for my 2cm resolution data source. Any other suggestions are really
appreciated.

On Sat, 11 Mar 2023 at 18:29, Johannes Kröger (WhereGroup) <
johannes.kroeger at wheregroup.com> wrote:

> That looks like the layer's resampling is not set to nearest neighbor.
>
> Also be aware that QGIS will have to resample the tiles whenever the
> scale of the map does not match one of the pre-rendered zoomlevels of
> the source (and the same CRS). If you have a matching CRS, select the
> layer and click the "1:1" zoom icon, the image *should* match the
> original 100%.
>
> Cheers, Hannes
>
> Am 09.03.23 um 15:55 schrieb Richard Duivenvoorde via QGIS-User:
> > ( bringing it back to the list :-) )
> >
> > And are you sure the image retrieved from the xyz server is not a jpeg
> > (compared to your original png)?
> > You can try to see the actual url's used via F12 (the Debugging
> > Development Tools panel) in QGIS.
> >
> > Another option: QGIS does not respect the xyz-zoomlevels always.. so
> > it is very easy to go to a zoomlevel in which QGIS has to resize the
> > original image a little (and 'resample' it, see Rendering/Raster
> > settings in the Options). So to really compare QGIS image to the
> > original one, you have to use the 'Zoom to native resolution' in the
> > legend/layer context menu).
> >
> > Last idea: is your project in the same CRS as the xyz service
> > (probably EPSG:3857?) Because if not, QGIS will also resample your
> > original image to 'fit' the tile in the right position in that other
> > crs....
> >
> > (and again: I know nothing about Qt image rendering ....)
> >
> > Regards,
> >
> > Richard Duivenvoorde
> >
> > On 3/9/23 15:36, Stephane Goldstein wrote:
> >> I can see the difference by comparing the .png file in an image
> >> editor (https://pasteboard.co/YodS7tuhtzSC.png
> >> <https://pasteboard.co/YodS7tuhtzSC.png>) and how it's rendered in
> >> QGIS (https://pasteboard.co/tcGLRc7XrsNj.png
> >> <https://pasteboard.co/tcGLRc7XrsNj.png>).
> >> The examples are at the same zoom level.
> >>
> >> On Thu, 9 Mar 2023 at 21:46, Richard Duivenvoorde
> >> <rdmailings at duif.net <mailto:rdmailings at duif.net>> wrote:
> >>
> >>     On 3/9/23 14:05, Stephane Goldstein via QGIS-User wrote:
> >>      > Hi.
> >>      > Is there a way to disable anti-aliasing of the png tiles
> >> loaded on an XYZ layer ?
> >>
> >>     Hi Stephane,
> >>
> >>       From what do you conclude that there is anti-aliasing going on
> >> with XYZ layers?
> >>     I use xyz layers also but I'm not aware of such behaviour?
> >>
> >>     FYI: this is the code rendering the images:
> >>
> https://github.com/qgis/QGIS/blob/master/src/providers/wms/qgswmsprovider.cpp
> >> <
> https://github.com/qgis/QGIS/blob/master/src/providers/wms/qgswmsprovider.cpp>
>
> >>
> >>     (tried to search for 'alias' but could not find anything)
> >>
> >>     Note, I'm not an expert in this field, so just wondering...
> >>
> >>     Regards,
> >>
> >>     Richard Duivenvoorde
> >>
> >>
> >
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> --
> Johannes Kröger / GIS-Entwickler/-Berater
>
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