Why are my RAW images so dark?
In 16-bit mode, many are surprised that a relatively dark photograph shows up after RAW conversion with digiKam, even so the 'ColorManagement' and 'RAW Conversion' options have been meticulously set-up for the intended purpose. The simple reason is that digiKam uses Dave Coffin's dcraw for linear conversion, and if the ICC profile does not include gamma correction and/or tone mapping (most Canon profiles), the result is dark (in 8-bit mode the gamma correction is applied automatically). But nothing is lost, read on!
A RAW file is a container including the raw sensor data, EXIF metadata, and often a JPEG preview thumbnail. It does normally not include an ICC profile. The embedded JPEG file is used by digiKam to display RAW image thumbnails or in slide shows, and it can be used for TV display from the camera. This is fast, but a preview only, no raw data.
RAW conversion requires a couple of steps in order to produce a satisfying result, better adapted to your needs than JPEG out-of-the-camera images:
- Choice of the internal working space in regard to the intended use
- Adjust tonal range - define thresholds for highlights and shadows
- Adjust gradation - adjust mid tones, for example using numerical numbers in the histogram or curves like features
- Alter white balance if necessary
- Color cast removal ideally using color temperature (or an according eyedropper tool) as well as a tint / tone slider. An according eye-dropper tool can be applied simply by clicking inside the image on neutral grey subject tones. This procedure doesn't always create the expected result, because quite often the light situation while capturing the image wasn't neutral either.
- Smoothing and noise removal (if not done in the conversion process already)
- Apply sharpening (refocus, unsharpmask)
- Choose final color bitdepth (saving as JPEG always reverts to 8-bit depth, use PNG or TIFF for 16-bit)
- Select output and pixel dimensions – upsampling on the RAW file often gives better results in comparison to already processed files
- Continue editing for example retouching or small enhancements in the favorite imaging application
Now, most profiles that come with the camera OEM software are not so suited for linear conversion. If you'd like a good profile, do it yourself or via a service. It will be more precise than the standard profile and it will include gamma correction - no dark images anymore in 16-bit mode!
Some good reading on the subject: