Hi, nope this isn't what I want ... it is the same as setting transparent color manually.
I am using PDF and TIF for georeferencing. Regards Without no-data-0 or transparent-color: Set transparent-color to 0,0,0 or use no-data-0: Am 01.10.2021 um 19:26 schrieb Charles Dixon-Paver:
I just loaded an unreferenced png with black content into qgis, then set the nodata value to 99999, then did a fake georeference with arbitrary coordinates, and the result seemed to be rotated without any background pixels. Using 3.20 on Windows. The geoereferencer has a checkbox for setting nodata to 0, so uncheck that first. Otherwise, if you're still unable to get the "triangles" to change, my previous messages should still apply. On Fri, 1 Oct 2021 at 18:27, L.W. <[email protected] <mailto:[email protected]>> wrote: yes, maybe to orange, a color that is not in the original image, so I can do this color transparent. Am 01.10.2021 um 18:25 schrieb David Strip:When georeferencing, aren't the areas outside the original image, eg, the "triangles" resulting from rotation, treated as no data? Wouldn't this issue be resolved by setting the no data value to something other than black? Just guessing here, obviously. On 10/1/2021 2:36 AM, L.W. wrote:Thanks for answering, but I think this is not the way I want to go ... Or, I do not have written detailed. I have a raster image e.g. a white rectangle, after setting the points, QGIS rotats this image, let's say, by 45 degrees. The corners of the imported image are now black triangles. I do want to have e.g. red triangles ... Regards Am 01.10.2021 um 09:50 schrieb Charles Dixon-Paver:There's not really any way for a GIS system to automatically differentiate between black background pixels and black data pixels. QGIS supports users setting custom pixel values to render as transparent pixels, but it's left up to users to ensure that their data and background values are different. From my view, there are a couple of options when it comes to fixing this issue in your data. One is to use an image processing tool like GIMP or Photoshop effectively, but that requires retaining the geographic information and knowing how to reprocess the raster accordingly. The simplest solution I'm aware of is probably to follow this workflow in QGIS: * Start a new QGIS project * Set all black pixels to transparent in the transparency tab of the raster layer properties * Digitize a "bounding area" - you can do this with a memory layer * Move your vector layer to render underneath the raster * Give the vector a simple black symbology * Use the "Convert map to raster" tool from the processing toolbox There are a wide number of variations on that workflow that are possible of course, but I think that's the easiest to get started.
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