Posts Tagged ‘raw’
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.
Process RAW Files with Rawstudio
Photo management software like digiKam can help you to process, organize, and manage your photos, but if your photographic workflow is built around RAW files, then you might consider a more specialized application like Rawstudio. This software darkroom offers a wide range of powerful tools for sorting and processing your digital negatives. Although Rawstudio is designed for serious amateurs and professional photographers alike, the application sports a slick and user-friendly interface which puts all the essential tools at your fingertips and makes it easy to get to grips with this powerful application.
The first order of business is, of course, to install Rawstudio on your machine. Ubuntu users will be pleased to learn that the latest version of the application is available in the official software repository, so you can install Rawstudio from the Ubuntu Software Center or using the Synaptic package manager. On other Linux distros, you can compile Rawstudio from source using the standard ./configure; make; make install routine.
Before you start using Rawstudio, it’s a good idea to adjust the default settings. To do this, choose Edit » Preferences. By default, Rawstudio creates a hidden .rawstudio directory in every folder you open in the application. Rawstudio uses these hidden directories to save image settings, such as basic adjustments, crop, rotation, etc. If you prefer to store this information in a single location in your home directory, tick the Place cache in home directory check box in the General section. In the Quick export section, you can specify output settings, including file format, color space, and destination directory. Here you can also define a custom file naming rule using several variables. To see a list of available variables and their brief explanations, press the plus button next to the Filename template drop-down list. In addition to standard file formats such as JPEG, TIFF, and PNG, Rawstudio can upload processed photos directly to popular photo sharing services like Flickr, Picasa, and Facebook.
Once you’ve configured the settings, you are ready to put the application to some practical use. Rawstudio’s interface is split into three main areas. The thumbnail bar at the top displays thumbnails of photos in the currently opened directory. The preview pane displays a large version of the currently selected photo, and the sidebar to the left gives you access to essential editing and tweaking tools.
There are two ways to add RAW files to Rawstudio. Using the File » Open Directory command, you can pick a folder containing RAW files. Alternatively, you can use the Open tab in the left sidebar to navigate and select the desired directory by double-clicking on it. In addition to that, Rawstudio supports tethered shooting, so you can plug your camera to your computer and take photos directly from within the application. To evoke the Tethered Shooting dialog window, press F9 or choose View » Tethered Shooting. Select your camera from the Select camera drop-down list and press the Connect button to establish a connection between the camera and Rawstudio. Press then the Take Photo button. Your camera should take a shot which is then automatically transferred to Rawstudio.
Rawstudio lets you assign a priority to each image using the number keys from 1 to 3, which can help you to triage your RAW files quickly and efficiently. And you can use the tabs in the thumbnail bar to view RAW files by their priorities. The application includes basic tagging capabilities, too. Select the RAW files you want to tag in the thumbnail bar and press Alt+T (or choose the Photo » Tag Photo command). Enter the desired tags separated by spaces, and hit the Apply button. You can then filter photos by a specific tag using the Tag search feature in the Open section.
Most of Rawstudio’s photo tweaking tools are tucked under the Tools tab in the right sidebar. The application allows you to work with up to three versions (or snapshots) of the RAW file simultaneously, and each version has its own tab: A, B, and C. This allows you to try different settings, compare the results, and pick the one you like. All tools in Rawstudio are grouped into collapsible sections. Using the tools available in the Basic section, you can adjust exposure, saturation, hue, and contrast as well as sharpen and denoise the photo. You can use sliders to adjust each parameter, or enter exact values for more precise control. To do the latter, click on the number next to the parameter you want to adjust, and enter the desired value in the appeared pop-up window. Options in the Channel Mixer section allow you adjust red, green, and blue colors, while the Lens Correction section contains lens correction tools that can help you to fix chromatic aberration and vignetting. As the name suggests, the Curve section offers a tool for tweaking the photo’s curve, and you can quickly flip and rotate the photo using the tools in the Transform section. You can individually reset most of the parameters to their default values by clicking on the parameters’ labels. Alternatively, you can reset all the parameters in one fell swoop by using the Edit » Reset settings command.
There are a few other handy tools hidden in Rawstudio’s interface. The Photo menu, for example, contains commands that allow you to crop and straighten the photo. The View menu offers a couple of useful commands, too. The Exposure Mask tool highlights overexposed areas in the photo, making it easier for you to adjust exposure settings. Using the Split command, you can display two snapshots side-by-side, so you can easily compare two different versions of the photo. Finally, the Lights out command dims the interface, making the photo stand out.
When it comes to saving the converted and tweaked RAW files, Rawstudio offers three options. You can use the File » Quick Export command to save the currently opened photo using the default export settings. Alternatively, you can use the File » Export As command to change export settings on the fly. To export multiple photos, you need to add them to the batch queue first. To do this, select the photos you want to export in the thumbnail bar, then choose the Batch » Add to batch queue command (or use the Insert key). Under the Batch tab in the right sidebar, adjust the export settings to your liking and choose the Batch » Start command to run the batch export.
Process RAW Files in digiKam
digiKam usually does a decent job of decoding RAW files using the default settings. But if you prefer to have complete control of how the application processes RAW files, choose Settings » Configure digiKam, switch to the RAW Decoding section, and enable the Always open the Raw Import Tool to customize settings option. Next time you open a RAW file for editing, digiKam drops you into the RAW Import interface where you can tweak the RAW import and post-processing settings. digiKam relies on the LibRaw library for all RAW processing. LibRaw is a pure C++ library which includes demosaicing algorithms from the dcraw software as well as algorithms from other projects like Rawtherapee.
The RAW Import sidebar contains three tabs: RAW Decoding, Post Processing, and Info. The RAW Decoding section gives you access to settings that let you tweak demosaicing, white balance, noise reduction and chromatic aberration correction, and color management settings.
Demosaicing is a process of reconstructing a full color image from the raw output of an image sensor. To better understand what demosaicing is and how it works, you might want to check the Understanding Digital Camera Sensors article. digiKam (or rather the LibRaw library) supports several demosaicing algorithms, including Bilinear, VNG, AHD, LMMSE, and others. You can use the Shift+F1 keyboard shortcut to view a brief, and rather technical, description of each algorithm. But the best way to see the differences between different algorithms is to try to apply them to the currently opened RAW file. Select the algorithm you want, and press the Update button to preview the result. The preview pane displays an image that will be imported in the editor, and you can use the zoom slider at the bottom of the window to zoom in on the image for closer examination.
By default, digiKam converts RAW files into 8-bit color images, but you can choose the 16-bit mode instead by enabling the 16 bits color depth option. The 8-bit mode is faster, but the 16-bit conversion is by far the best way to go, as it provides better tonal range. If you choose to work in the 16-bit mode, it’s recommended that you enable and configure color management options in the Color Management section to prevent dark rendering of the image in the editor. Due to the way certain algorithms process green pixels, the resulting image can contain undesirable patterns and artifacts. Enabling the Interpolate RGB as four colors option can fix that. The Do not stretch or rotate pixels option is there specifically for Fujifilm’s cameras with the Super CCD sensors and cameras using sensors with non-square pixels. When this option is enabled, the image is titled 45 degrees, so that each output pixel corresponds to one RAW pixel. This option also prevents the image from stretching to its correct aspect ratio.
In the White Balance section, you can adjust white balance settings and specify how the system should handle highlight clippings (overexposed areas in the photo). LibRaw offers several algorithms for restoring highlight clippings — Solid White, Unclip, Bend, and Rebuild — and you can view their brief description by using the Shift+F1 keyboard shortcut. To process highlights more accurately, enable the Correct false colors in highlights option. And if you want LibRaw to automatically adjust brightness, tick the Auto Brightness check box. Besides white balance, you can also enable and adjust the Exposure Correction option and manually tweak exposure compensation settings. The under- and overexposure buttons at the bottom can identify under- and overexposed areas of the photo in the preview pane, which can help you to adjust exposure settings.
Using the options in the Corrections section, you can choose to apply one of the supported noise reduction algorithms to the image as well as enable the chromatic aberration correction option and adjust its settings. And in the Color Management section, you can specify a color profile and a color space (refer to Color Management in digiKam for more info on color management).
Under the Post Processing tab, you can adjust several exposure settings (e.g., brightness, contrast, gamma, and exposure) as well as adjust the luminosity curve. While these adjustments can be performed later when editing the converted image, you can choose to do this during the RAW import to streamline the editing process. digiKam applies all adjustments to the preview image, so you can immediately see the result of your tweaking without performing the actual conversion.
Once you’re satisfied with the settings and adjustments you made, press the Import button to import and process the RAW file. And remember: if in doubt, you can always press the Use Default button to let digiKam import the RAW file using the default settings.
Editing RAW Photos on Linux with Rawstudio 2.0
The Rawstudio raw photo editor made its 2.0 release on April 8, boasting a hefty list of improvements. There are new features, such as tethered shooting and automatic distortion correction, almost every tool in the toolbox has seen an improvement — including some you might not think needed improving. If you shoot with a raw-capable digital camera, it’s time to update. Continue to read
Convert RAW Files to DNG with DNGConverter
digiKam comes with a nifty batch utility that allows you to convert RAW files to the DNG format. The question is, of course, why you would want to do that. After all, digiKam can handle RAW files without any problem, so what’s the point of adding one more step to your photographic workflow?
As you might know, RAW is not a file format, but rather an umbrella term that describes multiple file formats controlled by multiple hardware manufacturers. The RAW formats themselves are specific to digital camera manufacturers. For example, Canon cameras store RAW files in the CR2 format, while Nikon cameras use the NEF format. Besides being proprietary, RAW formats are often poorly documented and encumbered by patents.
The Digital Negative (DNG) format introduced by Adobe Systems, Inc in 2004 is designed to overcome these shortcomings by providing an open, well-documented universal format for storing RAW files. If you would like to know more about the DNG format, the DNG articles and links Web site provides a wealth of valuable information on the topic.
Being an open and well-documented format, DNG is suited particularly well for long-term archiving of digital photos. Of course, the CR2 and NEF and other RAW formats are widely adopted and supported, so they are not going away anytime soon. But there is no reason why you shouldn’t save your RAW files in the DNG format to be on the safe side. After all, storage is cheap nowadays, and the DNGConverter utility makes it supremely easy to convert RAW files to the DNG format.
Using DNGConverter couldn’t be easier. Launch the utility, add the RAW files, specify a few options, and hit the Convert button. For complete peace of mind, you might want to enable the Embed Original File option which embeds the source RAW file into the resulting DNG file.
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.
