I use PDF as well, there you can not save a background-color or
something like that.
This should be better an option in QGIS to "set the colors of the black
recangles" ;-)
thanks all.
Am 01.10.2021 um 23:19 schrieb Nicolas Cadieux:
Hi,
It's quite simple, you just need to set the nodata value (what you
call the background-color) in the original file and then save it. The
complication is that this requires that the datatype for the file
accepts the no data value. This part is harder to figure out for your
not used to dealing with datatypes. Perhaps, what should be asked
for is a check to see if the nodata in the translate tool check in
compatibility with the datatype format. Another possibility is to
allow for setting the nodata value (other than zero) in the
Georeferencer tool (for both the input file and the output file).
Nicolas
On 2021-10-01 4:04 p.m., L.W. wrote:
sounds like rocketscience ... for a simple task to set the
background-color ...
may be I am searching the web where I have to place my feature
request for this ...
Am 01.10.2021 um 21:39 schrieb Nicolas Cadieux:
Hi,
Start by setting the nodata value in the input raster.
(raster/conversion/translate/Assign a specific nodata value to
output bands). Make sure you select a data type that allows your
nodata value. For example, if you select Byte - Eight bit unsigned
integer, and a no data value of *-999*, -999 does not exist in that
data type so the nodata values will be 0 therefore affecting all
black pixels in the image. Select something like int16 of
float32... and a no data value of -999 for the test. Load the new
raster and in the layer properties, make sure you have been
successful changing the nodata values.
Then, when georeferencing, make sure you *DO NOT select "Use 0 for
transparency when needed".* The nodata from the georefrenced file
will be taken from the original file (-999). Therefore, pixels with
the value 0 in the image will not be affected.
Nicolas
On 2021-10-01 2:33 p.m., L.W. wrote:
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.
_______________________________________________
Qgis-user mailing list
[email protected]
List info:https://lists.osgeo.org/mailman/listinfo/qgis-user
Unsubscribe:https://lists.osgeo.org/mailman/listinfo/qgis-user
--
Nicolas Cadieux
https://gitlab.com/njacadieux
--
Nicolas Cadieux
https://gitlab.com/njacadieux
_______________________________________________
Qgis-user mailing list
[email protected]
List info: https://lists.osgeo.org/mailman/listinfo/qgis-user
Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
