Basic RAW Processing in digiKam
For this project, we’ll use a photo of the famous Sagrada Familia cathedral in Barcelona, Spain (you can download the RAW file from https://www.box.com/s/cq3uknqt54o3usf1jg3r). The photo was taken with a Canon PowerShot S90 camera, and the RAW file exhibits several obvious flaws, including visible barrel distortion, underexposed areas, and noise. In other words, this particular RAW file is perfect for tweaking in digiKam.
Configuring RAW decoding
Before you start, make sure that digiKam is set to open RAW files in the 16-bit mode using the default settings. To do this, choose Settings → Configure digiKam and switch to the Raw Decoding section. Enable the Use the default settings, 16 bit option and press OK. Open then the RAW file for editing using the F4 key (or choose Image → Edit).
Applying lens correction
The first order of business is to fix the lens distortion. Since the LenFun library used by digiKam for automatic lens correction doesn’t have a lens profile for Canon PowerShot S90, you have to fix lens distortion manually. Choose Enhance → Lens → Distortion, then use the Main slider to set the correction value. Alternatively, you can enter the exact value in the field next to the slider. For this particular file, the -27 value should do the trick. Check the preview image to make sure that the distortion is properly corrected, and press OK to apply the correction.
Using the Local Contrast tool
Although the Canon PowerShot S90 did a respectable job of producing a well-exposed image, the photo still has slightly underexposed areas. The easiest way to fix this problem is to use the Local Contrast tool (Enhance → Local Contrast). The default values should do the trick, but feel free to experiment with different settings. But don’t try to push them too far, as the final result may look unnatural. Also, before you start modifying the default settings, save them as a preset using the Save As button. Later, you can restore the original settings from the preset using the Load button.
Applying noise reduction
Next stop is the Noise Reduction tool (Enhance → Noise Reduction). While the default noise reduction settings work fine in most situations, you might want to adjust them to achieve even better results. When experimenting with different noise reduction settings, it’s a good idea to switch to the 100% crop, which gives you a much better view of the noise reduction effect. To do this, select 100% from the Zoom drop-down list. You can then use the scrollbars to view the desired part of the photo. Alternatively, you can use the Pan button in the lower-right corner of the preview window to display a thumbnail of the photo and pan by dragging the red square to the desired area in the image. To preview the noise reduction result, use the Try button.
Sharpening the photo
Finally, the photo could use some sharpening, so choose Enhance → Sharpen, adjust the sharpness level using the Sharpness slider, and press Try to preview the result. Again, you might want to switch to the 100% crop for a better preview.
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Posted in Open Source, Software
3 comments on “Basic RAW Processing in digiKam”
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Spanky says: 2013/03/12 at 04:02
Thanks for your work, but I have a differnt perspective.
The S90 lens is soft, and high ISO also takes away quality.
I have always found the Digikam Raw developers weak; when compared to ufraw. ufraw can work as an automatic compliment to Gimp, is that linking package (gimp-ufraw) is simply installed.
ufraw appears strange to new users who have not read the onilne ufraw page. Some people atempt to use it without loading their camera profile, as the ufraw page easily describes. Then, there’s a bunch of control in ufraw; but you never need to change all of them. Only a few, and only when needed.
What’s great is, with your camera profile, you can tweak your Raw file, to MATCH your preferred JPEG output (even on other camera brands; at the given sensor ability), and I am saying, just as soon as ufraw loads up your picture!
A. Shoot only Raw, and pull the JPEG’s out, with dcraw instantly (not Raw develping).
B. Only do very select Raw pictures; where needed.
C. ufraw properly setup, and just the first time, loads your largely finished Raw job.
All the things you can do, are covered as the ufraw web page. You should understand, curves are the better, and more professional way to handle Raw changes. The first curve is more for large batches, and you can skip it, and twael the seconf curves, if needed, per picture. These “local contrast” edits, act like a per picture, D-Lighting, I-Exposure, or HDR adjustments; with your full Raw data(latitide). Watch a video on adjusting with curves, if you have never done it. THere is also an “eyedropper”, to set any white balance, that wasn’t alreaady set before you took the picture.
JPEG’s can go straight to Gimp, and Gimp has numerous plugins that you should install, for one click treatments. It’s a lot of power; but that’s exactly why Gimp is your one stop shop, for just about anything you would need, for you photo edit. Learn it well. It isn’t less, because it’s free to you. It is better, and at any price.
Raw files, if loaded with Gimp, with automatically go through ufraw, smoothly. Raw files loaded with ufraw, then has a Gimp button, taht automatically put the out put into Gimp; where you can eventually save/export it as your final JPEg (or whatever). You may of course, save you ufraw output, as a .PNG file; In case you wish to pass it through many, different editors (like for testing).
I especially like saving to JPEG, from Gimp; because Gimp automatically sets the JPEG compression level to it’s optimum (variable per photo) balance.
Gimp’s NR (with color vs, luminance correction) is awsome. It’s lens distortion correction is awasome, and I have a “Darla” script, that automatically remove color frinding, if needed.
DigiKam is good for tagging/rating.
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GrueMaster says: 2013/03/12 at 17:58
I think you are slightly missing the point of this article. While I agree that the Gimp is far more powerful for photo editing, I think the focus here is using one app to manage all of your photo needs (for most users).
I personally use both. If there is something I need to do that Digikam won’t do well (like removing date stamps off my mother’s digital photos), I switch to Gimp to process them individually. It takes more time, but I have more capabilities for that type of work.
I do like your brief tutorial of Gimp and UFRaw. Maybe you should post a full tutorial article on it.
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Albin says: 2013/03/12 at 16:56
Thanks for the article and the interesting comment by Spanky. I’ll be moving from an older version of PS Elements on XP, and want some equivalent quality tools without Java security issues. I’ve had GIMP/UFRaw for a while in Linux, and it has the advantage of Windows versions for consistency. Only recently learned of Digikam and it’s great to see a learner’s intro to it.
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