Archive for November 2009
Color Management in digiKam
First of all, what’s color management? Color management is a process that allows you to achieve consistent color representations across different devices, such as digital cameras, scanners, printers, and monitors. The key concept in color management is color space — a model that describes the way colors can be represented as numbers. The Dry Creek Photo page explains it best:
A color space provides the definition for what color the numerical combination represents. Color spaces are akin to languages. A value such as 88/249/17 is given meaning by the color space in the same way as an otherwise random sound has meaning in a particular language. If our example of 88/249/17 is interpreted using the Adobe RGB color space, it is a vibrant, attention getting green. If, on the other hand, the same value is interpreted using the sRGB color space, it is a pale, sickly yellowish-green.
In most cases, you don’t have to worry about color management (see Ken Rockwell’s explanation why color management is a non-issue for most photographers). But if you do need to take control of colors, digiKam’s got you covered.
To enable the color management feature in digiKam, choose Settings -> Configure digiKam, switch to the Color Management section, and tick the Enable Color Management check box in the Behavior section. Next, choose the desired color space from the Working Color Space drop-down list. digiKam supports several color space models, including Adobe RGB and sRGB. Which one to choose depends, of course, on your needs (the sRGB vs. Adobe RGB article by Ken Rockwell provides an excellent overview of the two most popular color spaces). The Behavior section also allows you to specify how digiKam should handle photos with profiles that don’t match the working color space, images with no profiles, and raw files with uncalibrated colors.
For example, you can set digiKam to display a color space conversion dialog when the photo you are about to edit uses a different color space than the one you selected in digiKam (see screenshot above).
In the Profiles section, you can specify color profiles for your monitor and peripherals such as camera, scanner, and printer. Obviously, you’d want to select the same color profiles as the working color space. Finally, in the Advanced section, you can enable the Use black point compensation feature which provides a way to adjust black levels of files to match the capabilities of digital devices to manage black.
Finding Geotagged Photos in digiKam
Need to find all the photos you took in France? You can use the Map Searches sidebar to do just that, provided your photos have been geotagged.
Expand the Map Searches sidebar, press and hold the Ctrl key and select the desired region on the map using the mouse. You should then see markers on the map. Each marker displays the number of found photos in the specific location, and you can use the mouse or zoom buttons to zoom in on the map to see thumbnails of the found photos. You can also see all found photos in the main pane. If you press and hold the Shift key and then click on a marker on the map, digiKam will highlight all the photos belonging to this group in the main pane.
digiKam also allows you to save map searches. This way, you don’t have to perform the same map search every time you need to find photos in a specific region. Enter a name for your search in the field below the map and hit the Save button. This adds the search to the My Map Searches section, and you can activate the saved search at any time by clicking on it.
By the way, digiKam supports both Marble and OpenStreetMap maps, so you can use the map you like for viewing the found photos in the Map Searches sidebar. You can switch between the Marble and OpenStreetMap maps using the Map Settings button.
Thanks to Gilles Caulier for the tip.
Geotagging Photos with digiKam
Even if your camera doesn’t support geotagging, you can easily add geographical coordinates to your photos using digiKam.
In digiKam, select the photo you want to geotag and choose Image -> Geolocation -> Edit Coordinates. This opens the Edit Geographical Coordinates window containing a map. Drag the map with the mouse and zoom on a specific area to locate the exact place where the photo was taken. Alternatively, you can use the Search field to enter the address, for example: botanic garden, berlin, germany. Hit then the Search button, and you should see a list of found places that are marked with pins on the map. To add geographical coordinates to the photo, click on the exact spot on the map to add a pin to the place where the photo was taken. You can then drag the pin with the mouse to adjust the pin’s position. Hit then OK, and you are done.
If you use a GPS device to record your track when shooting photos, you can use digiKam’s Correlator tool to geotag the images (mapping photos using a GPX file is often called geocorrelation). To do this, you have to export the recorded track from your GPS unit as a GPX file. In digiKam, select the photos you want to correlate, choose Image -> Geolocation -> Correlator, then press the Load GPX File button and select the GPX file. Hit then the Correlate button, and digiKam does the rest. Keep in mind that for this feature to work properly, the time on your GPS device and digital camera must be in sync. If the time on both devices differs, you can specify the time gap in the Difference in min[utes] field.
Once you’ve geotagged your photos, you can view them on the map without leaving the convenience of digiKam. To do this, click on the Geolocation sidebar to expand it, select the photo you want, and you should see it on the map. digiKam even lets you choose between different map providers, including Google Maps, OpenStreetMap, and MSN Maps. To switch to the desired map, choose it from the drop-down list at the bottom of the Geolocation sidebar.
Quick Notes
- digiKam can geotag photos in the JPEG and RAW formats.
- If your GPS device doesn’t support GPX format, you can use the GPS Babel tool to convert the device’s proprietary format to GPX.
- In the future, digiKam will support Marble and OpenStreetMap for offline geotagging.
- Nokia has recently opened their map web service API, so it’s possible that digiKam will provide support for Nokia maps in the future.
Thanks to Gilles Caulier for the comments.
Moving to digiKam
For ages, I’ve been using Google Picasa to manage and tweak photos I took with my point-and-shoot cameras. Its editing tools are pretty limited, and the Linux version is just a not-so-pretty port that runs in Wine. When I moved to a DSLR camera these and other limitations became even more apparent. So when Google released Picasa 3.5 for Windows, leaving Linux users behind with the older 3.0 release, I decided that it was time to move on. After testing different photo editing and management applications for Linux, I settled for digiKam.
For many serious photographers using Linux, this is probably an obvious choice, since digiKam offers pretty much all the features you’d expect from a competent photo management application. Of course, as a writer who covers Linux and open source software, I knew about digiKam and even wrote a few articles about it. But at that point, it was overkill for my needs. Now, however, digiKam is exactly what I need. It can handle raw files and it offers excellent organizing tools (tagging, geocorrelation, star rating, powerful filtering options, etc). digiKam also provides an impressive collection of photoediting and batch processing tools as well as a sharing feature which lets you upload your photos to popular photo sharing services like Flickr, Picasa Web, and SmugMug. All in all, digiKam is a real gem, and I’ll be donating a few euros to the project.
