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I am currently working with a high-quality PDF file that displays perfectly when viewed in Adobe. However, when I import this file into QGIS for georeferencing, the quality significantly degrades and the image becomes pixelated.

I've tried various settings within QGIS to improve the image quality, but so far, I haven't had any success. I'm wondering if there might be a workaround within QGIS that I'm not aware of that might handle this type of high-quality PDF better for georeferencing purposes.

How can I maintain the original quality of the PDF when importing it for georeferencing in a GIS application?

Original file screenshot when opened in Adobe

enter image description here

Screenshot of the same area after importing to QGIS for Georeferencing:

enter image description here

EDIT: After converting to TIFF format with DPI set to a higher value

After converting to TIFF with DPI set to a higher value

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  • Could you share some test data?
    – user30184
    Commented Jul 30, 2023 at 19:46
  • Asking for software opinions in GIS SE is asking to get your Question closed for being opinion-based. I suggest you Edit this to focus on the problem, not on alternative approaches.
    – Vince
    Commented Jul 30, 2023 at 19:50
  • @Vince I've deleted the question about opinion
    – Abhilash
    Commented Jul 30, 2023 at 20:19
  • It looks bad because your PDF is being loaded as a raster, you could try to get the vector data using a PDF-DXF (eg cloudconvert.com/pdf-to-dxf) or PDF-SHP (eg mygeodata.cloud/converter/pdf-to-shp) then georeference the vector. Disclaimer: I have never used nor specifically endorse these services, they are only provided as examples of services that exist.
    – Michael Stimson
    Commented Jul 31, 2023 at 2:17
  • @user30184 Sure here is one sample file for testing adur-worthing.gov.uk/media/Media,156286,smxx.pdf
    – Abhilash
    Commented Jul 31, 2023 at 7:53

1 Answer 1

Reset to default
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Since QGIS uses GDAL to load PDF files, we could set an Windows/Linux/iOS environment variable GDAL-PDF-DPI=300 to increase the raster quality from 150dpi (default) to 300dpi.

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    I have tried your solution. But for some reason it was not working i.e, PDF is not loading into the georeferencer. So I have used your idea and converted the PDF into TIFF format by using the below command. set GDAL_PDF_DPI=1200 gdal_translate -of GTiff -co "COMPRESS=DEFLATE" -co "PREDICTOR=2" -co "ZLEVEL=9" Media_156286_smxx.pdf output.tif I then imported the TIFF file for georeferencing. It worked out pretty well this way.
    – Abhilash
    Commented Jul 31, 2023 at 10:30
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    @Abhilash I'm glad I could help. Would add --config GDAL_CACHEMAX 1024 -co NUM_THREADS=ALL_CPUS -co TILED=YES to the command line to speed up translation and for image tiling. If your PDF has layers included, you could even remove the unnecessary ones. See all options here: gdal.org/drivers/raster/pdf.html
    – christoph
    Commented Jul 31, 2023 at 10:38
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    @Abhilash when I look at the sample PDF you have posted, it would be better to use JPEG compression for smaller size and faster loading: gdal_translate --config GDAL_CACHEMAX 1024 -co NUM_THREADS=ALL_CPUS -co COMPRESS=JPEG -co PHOTOMETRIC=YCBCR -co TILED=YES -co JPEG_QUALITY=90 -b 1 -b 2 -b 3 <source.pdf> <target.tif>. And use overviews: gdaladdo --config COMPRESS_OVERVIEW JPEG --config PHOTOMETRIC_OVERVIEW YCBCR --config GDAL_TIFF_INTERNAL_MASK YES -r cubicspline <source.tif> 2 4 8 16
    – christoph
    Commented Jul 31, 2023 at 11:03

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