Why shoot in RAW format ?
In collaboration with Christophe Gressin
In this tutorial, we will show you why it is a good idea to save your photos in RAW format when shooting. We will explain what RAW format is and the advantages it provides during processing.
To follow this tutorial, you will need:
- DxO OpticsPro 10, Essential or Elite edition
- Some photos, preferably shot in RAW+JPEG format
1-The principal differences between RAW and JPEG
To understand the benefits of shooting in RAW, let’s first take a look at how a camera transforms light signals into an image.
All cameras save the data that their sensors receive in RAW format. This information comes from transforming the light signal that comes through the lens into digital data that the camera uses to reconstruct the colors in an image.
The camera sensor is equipped with color filters that enable each photosite to save a specific color (red, green, or blue), and the photosites are distributed within a “Bayer matrix” (per the illustration below).
Simply put, three steps are required to create an image from sensor color data:
- Demosaicing, which consists of reconstituting all of the color information from the data saved on each photosite;
- Converting the data collected by the sensor into reference colors, which requires having calibratrated the way the sensor perceives colors;
- Applying the color rendering chosen by the manufacturer (and thus characteristic of that particular camera).
These operations are similar to the processes needed to develop an analog film cartridge. Each software program has its own processing algorithms that give different results than those of other programs.
JPEG format is the most common format for recording photos and one which all cameras use. The file is created via the operations described above, followed by a compression phase.
In a digital camera, saving the file is the last step of image capture. When you choose to save your photos in JPEG format, the camera will save only the final result. While all of the RAW data is still processed by the camera (according to its manufacturer’s algorithm), it will not be saved.
When you save your photos in RAW format, a JPEG file is also systematically saved and included in the RAW file. It is created with the same algorithm that would have been applied had you simply chosen the JPEG format, and it is this file that your camera uses to display the image on the rear screen of your photo. Further, most viewers also use this JPEG file to display a thumbnail image of the RAW file.
This is why you will see differences in processing results between one software program and another, and especially why you may see a difference between the initial and the final display of the image in your software. So if you set your camera to black & white mode, for example, your photos will appear as black & white on your device screen, but they will open as color images in DxO OpticsPro.
As a matter of fact, camera manufacturers do not provide all the data nor the algorithms with which to convert a RAW file —particularly those that correspond to the color settings on the camera — so image processing software developers such as DxO have created their own algorithms in order to provide better results.
Is all of this complexity a disadvantage when compared to saving an image in JPEG format? On the contrary, it actually contributes to the richness of the RAW format, as we will see in the next section.
Why choose RAW format?
When you use a RAW converter, and DxO OpticsPro in particular, you benefit from extremely powerful algorithms that can fully exploit the potential of the RAW data.
Even better, the performance of these algorithms improves with each new version, thanks to advances in research and to the increase in computing power. That’s why it’s important to keep your RAW files, because tomorrow’s algorithms may be able to extract even more details that are not yet accessible today!
Conversely, when you generate JPEG files directly, the processing applied as well as the compression permanently destroys the data used to create the image, resulting in less leeway for correcting flaws.
In DxO OpticsPro, certain corrections are only available or have more precise settings in RAW than in JPEG, because the lack of data in the latter reduces their effectiveness.
All cameras, be they reflexes, compacts, or smartphones, internally produce all the information necessary to create a RAW file, but most only give access to the final JPEG file. In general, only high-end compact, hybrid, or digital reflex cameras allow you to save your images in RAW format.
2-Correcting RAW and JPEG files in DxO OpticsPro 10
Most cameras that shoot in RAW also have a RAW+JPEG mode that generates a RAW file and a JPEG file simultaneously, thus allowing you to have a file that is instantly usable as well as one that is better suited for enhancement.
We will now show you some examples of corrections applied to a RAW file and a JPEG file for the same image.
For each example, we will start by applying the “No correction” preset so as to start off with the crudest image possible, and then we will show the JPEG and RAW corrections separately. When actually working on your images in “real life,” we advise you to start from the “DxO default” preset, which is automatically applied to your image upon opening it.
2.1 – Exposure
RAW files allow you to recover the details in highlights and shadows that you might think are forever lost in a JPEG file.
Let’s now work on an image to try to recover the details in an overexposed sky. To do so, we will use the Highlights slider in the Selective tone sub-palette. By setting the slider to –100, we will darken the highlights and thus recover details in the sky. We see a very limited recovery in the JPEG image: only a very small area of the overexposed clouds is balanced. With the RAW file, however, nearly the entire sky is correctly exposed.
To recover the details in the shadows, we will use another image for which we will modify the Tone Curve.
We will choose this correction because it acts in exactly the same way on both a RAW file and a JPEG file, unlike the Smart Lighting correction, for example, whose intensity depends upon the information available in the source file.
Here we can clearly see the difference in quality in the shaded parts of the image: the RAW file lets us obtain an image with less noise, better sharpness, and better colors.
2.2 – White balance
With a RAW file, you can adjust the white balance exactly as if it were a setting on your camera (daylight, cloudy, tungsten, etc.). With a JPEG image, all you can do is modify the overall temperature of the image, with a lower-quality result.
Below is an image for which we will use the eyedropper tool to adjust the white balance: after the correction, the image retains its natural look in RAW but loses its atmosphere in JPEG, which has introduced bland and faded colors.
The Hue slider lets you control the white balance more finely in RAW.
Here is a comparison of noise removal for a photo taken at 6400 ISO. You can see that the quality of the fine details is better in the RAW file, and especially when you use PRIME technology.
The images below are zoomed in at 100%:ettings.
JPEG before correction
JPEG after correction
RAW before correction
RAW after correction
Photos credits: Arnaud Pincemin