When it comes to raw digital photo processing, RawTherapee has always been part of the open source revolution and helps many professional photographers side-step Adobe's hegemony. But RawTherapee doesn't often get the same attention as darktable, which is a pity, because the two applications together are responsible for revolutionizing photo processing on Linux. If you're looking for a quick comparison, RawTherapee is slightly more Adobe-like, letting you do more within a single application than darktable's focus on post processing. In RawTherapee, it's easier to browse your photo collection via its file manager, for example, rather than scanning them into an internal database, and it will load hundreds of thumbnail previews from a randomly chosen folder much quicker. This makes it great for the unorganized photographer or perhaps the ambitious amateur, who hasn't sorted out their sorting yet.

RawTherapee also feels quicker when editing. It contains many of the same functions as darktable, such as exposure, shadows, darkness, sharpening, color correction, chromatic aberration removal, lens compensation, and many more, but their parameters are immediately accessible and tweakable, unlike the preset-enable-plugin nature of darktable. The effects aren't perhaps as subtle and are not as good at correcting photographic problems, such as underexposure or high contrast. But with careful editing of good source material, the output is almost as good as darktable's while using fewer PC resources. This is important if all you want to do is edit a virtual reel of holiday photos, rather than produce images for print or syndication. RawTherapee is also an application that's developing at an incredible rate, with version 5.7 adding support for film negative processing, image rating, and dozens of bug fixes. This means it's not so much about choosing one application, but simply having the choice to select the best open source tool for the job at hand.

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RawTherapee might not have the same fine-tuning as darktable, but it's faster to preview and navigate hundreds of images.

Spectral fitter


Spectral diagrams typically show changes in amplitude across the frequency range of a sample or measurement. In audio, for example, they can plot the frequency level of a slice of sound across the human audible spectrum. It's a great way to visualize a spike at 60Hz due to hum from the power supply or the 10KHz whine of a faulty capacitor. But in more scientific analysis, a spectral diagram might show just a single frequency with a few harmonics, and it can then be useful to create a function to describe the observed values outside of the plot. This is what the spectral fitter kfit does. You start by adding the data readings for your spectral plot. There's a tab for this, with columns for X and Y values, but you can also import a CSV file of external measurements. The plot is then drawn in the main window and you can start to create your fit.

Kfit has four fitting models: Gaussian, Lorentzian, Pseudo-Voigt, and linear. They're added using the plus and minus buttons for each type beneath the graph. You can add more than one at a time to get your fit as close as possible, and they each require a different set of parameters as you try to create something that fits. After adding the values you wish to try, you click on the Fit icon in the toolbar. This will draw your new curves across the original spectrogram. You can also change the size and scale of the workspace using a floating panel. When you do have output you can work with, it can also be exported via a CSV, or the data can be viewed from the main window's Output tab. That's about all there is to it – it's not as complex as using something like Mathematica, but its limitations make it ideal for use in education or if you just want to play around.

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Alongside being able to import and export data, you can save the graphs themselves as a bitmap or vector image.

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