[GIS] Why are JPG files invisible in Georeferencer

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I want to georeference a jpg file (map) with QGIS 1.8.0 on a Windows 7 (64 bit) machine.

The georeference window opens, but the map is not visible.
When converting the jpg file into a tif file (e.g. with gimp) everything works.
I tried it with several files. Always the same: The tif files are visible and can easily be georeferenced, while the jpg-files are not visible in the georeference window.

Any ideas?

Thanks for answers,
Ulli

Best Answer

When you save your JPEG in GIMP, expand the 'Advanced Options' when the 'Export as JPEG' dialog box comes up. Un-check the 'Progressive' box and then click 'Export'. Your JPEG is then readable in QGIS.

"Progressive" changes the encoding to display the image at increasingly higher quality levels until the image is fully loaded. QGIS is expecting standard encoding. Progressive encoding appears to be on by default in GIMP (at least in GIMP 2 - I can't remember for earlier versions).

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[GIS] How to transform a georeferenced JPG to a georeferenced TIF

You could use gdaltranslate.

gdal_translate -of GTiff  myFile.jpg myFile.tif

This will actually give you a geoTiff, not a tiff with a world file.

You could also try renaming your 'TGW' file to a 'TFW'.

[GIS] Help required to convert georeferenced (and rectified) TIFF orthophotos to georeferenced .JPG format

Perhaps the easiest way is to use the GDAL tools, which underpin many GIS and mapping systems out there. If you're dealing with lots of files, it is a fairly easy task to write a batch file or script to automate the process.

I'll make some assumptions here about your level of comfort with the command line, but hopefully it should be easy to follow.

First, obtain GDAL. For most Linux distros, there should be a package in your repository. For Windows, it is easiest to download either FWTools or OSGeo4W.

Next, you need to run the program gdal_translate which will do the actual hard work for you. For your needs, it is a fairly simple set of options:

gdal_translate -of JPEG -co "WORLDFILE=YES" <source_filename>.tif <dest_filename>.jpg

This just tells GDAL to output a JPEG image given your source file and a destination filename. It will create two files, the JPEG image itself, and a .jpw (or possibly .wld) file which contains the georeferencing information, without which it would just be a picture.

Best Answer

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[GIS] How to transform a georeferenced JPG to a georeferenced TIF

[GIS] Help required to convert georeferenced (and rectified) TIFF orthophotos to georeferenced .JPG format

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