Photographers swear by the raw format as opposed to JPEG, especially for post-processing. Are there really technical benefits or is this just plain pedantry?

1 Scepticism

The argument I've often heard is that the raw image format will carry more information to work with afterwards. Certainly, JPEG will drop what it can to save space: in particular, fewer colours will be kept and shapes will be approximated leading to artefacts. Then again, given the relatively high JPEG quality cameras record photos with and the epic resolution modern ones have to offer, will using the JPEG format really hamper any attempt to improve the picture as part of post-processing?

To find out, I recorded with a decent reflex camera the exact same picture in high-quality JPEG and raw format. In fact, I was pleased to see that it offers an option to write from one single shot a file for each of the formats, saving me the trouble of trying to make two pictures with different settings with the help of a tripod.

I'd have expected the two pictures to be visually identical. Not so, then. In fact the JPEG one looks more vibrant, which would already comfort me in my idea of not using the raw format. Another thing this little experiment teaches me is that it appears that using the JPEG format does more than removing perceptively redundant information: it also implicitly requests the camera to do some post-processing of its own. Finally, if you zoom in on the ridge of the mountain, you'll find that there is after all no perceptible artefacts, not even in the JPEG picture.

2 Post-Processing the Raw Photo

I never worked with the raw format before and I thought I'd take the first raw editor I could find. I schemed through a comparison of solutions for Linux which suggested that darktable was the closest match to Adobe Lightroom. I saw a friend achieve stunning results with Lightroom. So be it, then, darktable it is.

Using darktable is straightforward, the only difficulty being to find your way through the sheer plethora of modules which affect photos in various ways, and their countless parameters. I followed the Darktable Tutorial 2017 25-minutes video which got me up to speed and suggested some commonly useful modules.

Some purists will say that it's criminal to post-process pictures and that one should leave what the lens saw untouched. I certainly used to think so until I chatted with my photographer friend about it. She says that post-processing may be necessary to reflect not what the lens saw, but what your eyes saw. Certainly, when it comes to landscapes, I've always been frustrated to be unable to capture the colour liveliness and end up with rather bland shades – as those pictures, raw or JPEG, demonstrate. I didn't see a dark mountain beneath a cloudy sky with a dark tree in the foreground. What I saw – and what I originally intended to convey – was a brown mountain with patches of snow beneath a changing sky, and a green pine tree in the foreground. Which is why I attempted to highlight here with darktable:

I changed the exposure to cover a wider dynamic range (exposure module), increased the saturation (contrast brightness saturation module) to emphasise the green of the pine tree, upped the level of detail (local contrast module) and, as I realised I'd left the ISO setting rather high when I took the shot, dampened the noise (denoise (profiled) module). The resulting picture is as near as makes no difference what I saw with my bare eyes, much more so still than the already better-looking JPEG photo the camera had post-processed.

3 Post-Processing the JPEG Photo

Since the JPEG picture the camera had post-processed already looked better than the raw one, I thought it'd be even easier to make it look good with darktable. And so I applied the same modules (with the exception of denoise (profiled) as the camera processor had already removed most of it) with adequate parameters:

Much to my dismay, even though I got close, I never could manage to make the post-processed JPEG picture look as good as the post-process raw picture. The post-processed JPEG photo didn't have colours quite as vibrant, and this was particularly true of the green shades of the pine tree. The extra data that the raw format carries had its uses:

4 Outlook

I'm glad to say that I was wrong all along. Recording pictures in the raw format is key to being able to post-process them effectively. Now that I'll be more enthused to do so from now on, it's worth pointing out a few nice touches of darktable's. It's not one of those all-integrated photo editing suites that try to do it all for you and hide whatever might be going on with your files: you can still very much manage your pictures in your filesystem with commands of your choosing.

The original files will never be altered. All darktable does is to keep a lightweight XMP file, a mere XML file which describes how modules are applied to your picture. Better still, darktable comes with a command line interface expecting an input file, an XMP file and an output file to write to, so as to be able to script workflows.

5 References

• 7 Best Apps to Edit RAW Photos in Linux
• darktable
• Darktable Tutorial 2017 (NO BACKGROUND MUSIC)