How to Downscale JPEGs with QGIS


Propeller offers two JPEG download options of different resolutions for your orthophoto. If the higher resolution JPEG file size is too large to use with your software, or you would like a smaller file for sharing with others, you can use QGIS to downscale the file.

Note that this procedure uses the gdal_translate utility but can be performed via the QGIS interface. 

1. Download the orthophoto JPEG from your portal and extract the zip file's contents. There should be a .jpg and a .jgw file included. Make sure these are unzipped to the same folder.

2. In QGIS, go to Layer > Add Layer > Add Raster Layer. Then, select the JPEG file and open it.


3. In the Coordinate Reference System Selector that appears, select the reference system that your data is in from the list and click OK. You can type the name or the EPSG code in the Filter field to search for the appropriate system.


4. Once the file has finished loading, click on Raster > Conversion > Translate (Convert Format).


5. In the Translate (Convert Format) window that appears first, ensure that your JPEG file is entered in the Input Layer field (it should automatically be there, assuming it is the only file you have loaded into this QGIS session).

6. Click on the Select as type button for the Output file field. Choose where to save your downscaled JPEG and type in the desired filename. In the Save as type field, select JPEG JFIF from the list of options. Click Save.


7. Tick the Outsize box and enter the desired output size. The value entered here represents a fraction of the input image size you wish to resize (don't forget the % sign).


8. Once those details are complete, click on the pencil icon beside the text box with the gdal_translate script. This will grey out all the options above it and allow you to edit the script inside the text box.


9. At the end of the existing script, type" -co worldfile=yes" and click OK. You'll be notified by a pop-up window once the process is complete.


10. If you need a .jgw file, you can rename the created .wld file and change the file extension.



I still can't do it!

We wrote these articles to equip you with everything you need to get the job done on your own, but we understand that sometimes this isn't sufficient. If you're stuck, you can connect with our support team by clicking the support button on the top right corner of your user portal.