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Demosaicing
explained

Agathe Poupeney
Ballet of the Opéra National du Rhin - Pour le reste - Choreography: B. Bouché - Performers: J. LYON
Fuji X-H2S
50-140mm f/2.8
ISO 12000 - 1/250 - f/4.0 - 106mm
DxO PureRAW - DxO PhotoLab

How DxO
does it better

DxO's 20 years at the forefront of RAW image processing means that we can produce better results than other RAW conversion software. Here’s why.

Fundamental to
RAW conversion

When you trigger your camera’s shutter, all the light that strikes the sensor is recorded as RAW data, but this needs to be converted into a different format before it can be displayed on a screen. This conversion can happen inside the camera, creating output files like JPEGs or TIFFs on the memory card, or the camera can be set to record exposures as RAW files for conversion later on, using software like DxO PhotoLab or DxO PureRAW.

Whatever the process, for photographers who want to reproduce the highest quality and most lifelike rendering of a scene, the standard of this RAW conversion process can be crucial.

What is
demosaicing?

When you expose your camera’s sensor to light and look at the resulting image on the camera’s screen or your computer monitor, it’s easy to forget that the photo is not recorded in full color. In fact, the sensor records a series of values that indicate the intensity of light at each of its photosites.

These photosites are intrinsically sensitive to all light without any ability to perceive individual colors, so manufacturers overlay color filters on top of the sensor.

As such, only intensity data for red, green, or blue light are recorded at each photosite — similar to the cones in the human eye.

In most camera sensors, these photosites are laid out in an alternating pattern of two green photosites for each pair of red and blue ones, so the distribution is half green, one-quarter red, and one-quarter blue.

This pattern of light receptors creates a mosaic of data that needs converting to reveal the original colors.

Without this demosaicing, all you would get is an image made up of red, green, and blue pixels of varying intensity.

However, as mentioned previously, it’s not just a question of applying demosaicing, but rather how it’s applied that leads to the most faithful rendering of detail. Bad demosaicing can cause all sorts of visual errors at the pixel level. These include color artifacts, such as fringes on sharp edges and moiré effects on some high-frequency patterns, all of which look unnatural. For example, fine textures like fur or feathers can lose proper definition and see maze-like or random pixels generated within them.

Stefan Forster
Leopard, Namibia
Nikon Z9
100-400mm f/4.5-5.6
ISO 7200 - 1/25 - f/5.6 - 400mm
DxO PureRAW - DxO PhotoLab

Poor demosaicing is a particular problem for photographers who are attempting to produce large-scale prints with fine detail, and for those who are cropping to magnify the subject, such as when enlarging a wildlife photo. 

Good demosaicing increases the
effective resolution of the camera

For example, even though it does not increase the pixel dimensions of an image, a camera with a 20Mp sensor and good demosaicing could still produce more detailed images than a camera with a 40Mp sensor and bad demosaicing. So with optimal processing, photographers can ensure they are maximizing the performance of their camera’s sensor.

Antoine Mutin
Seoul, South Korea
Nikon Z6
35mm f/1.4
ISO 51000 - 1/6400 - f/2 - 35mm
DxO PureRAW - Adobe Lightroom

How does
it work?

Because only one-third of the actual color information in the scene has been observed, the rest needs to be extrapolated by an algorithm. There are many different demosaicing algorithms, but they all share the same objective: to take the recorded data and develop something plausible to our eyes.

For each pixel, surrounding pixels are sampled and the true color is predicted. If one pixel shows a high level of green light and those around it have very low intensities of blue and red, it can be assumed that the correct color is a strong, though not pure, shade of green.

But this simple algorithm assumes that each pixel has the same color as its neighbors. While that might be true for the majority of pixels, it can be very wrong in many instances; for example, where there is a sudden color variation, such as at an edge or on a texture.

To reach plausible results, the algorithm needs to make assumptions about the underlying scene. But these assumptions have to come from somewhere, so it needs to be trained.

Petr Bambousek
Violet-eared hummingbird
Olympus EM-1 Mark III
200mm f/2.8
ISO 3200 - 1/800 - f/2.8 - 200mm
DxO PureRAW - DxO PhotoLab

The mosaic that makes up this tiny part of the image could have multiple interpretations. The trick is to create algorithms that can make intelligent assumptions about what the original information was and reproduce it as accurately as possible.

What DxO does better
than the rest

Having been at the forefront of RAW image processing for more than 20 years, DxO’s algorithms have always been ahead of the curve. Today, we are able to read out even more pixels than the camera manufacturers themselves. That’s right — DxO might give you more pixels than what your Canon, Sony, or Leica gives you.

In addition, machine learning has allowed us to push RAW processing technology further. 
Historically, demosaicing and denoising have been run as separate processes. This brings a big disadvantage as whichever process is performed first will potentially undermine the quality of the second. DeepPRIME’s breakthrough is its ability to run these two processes simultaneously, allowing it to achieve an unprecedented level of quality.

For DeepPRIME, we fed a neural network with billions of example images during its training phase; this enabled it to learn which structures and patterns occur most frequently in the real world and how to recognize them in mosaiced images.

Built on empirical knowledge, the resulting algorithms yield consistently better results than any human-written algorithm has been able to achieve since digital photography was invented.

Conclusion

At DxO, we’ve led the research on how to denoise and demosaic RAW files, guaranteeing photographers the best possible results. If you’re using DxO PhotoLab 8 or DxO PureRAW 5, you can be certain to get perfectly processed images thanks to cutting-edge science.


For the passionate photographer.

Learn more about DxO