From IRCC we recommend reading and trying to understand, at least in general, about the process of building a digital image, so that you can incorporate elements and criteria to place yourself on the debate about digital manipulation.
RAW image (also known as a “digital negative”) is an image file that contains unprocessed data from a digital camera’s sensor. RAW is neither processed nor compressed. In fact, the RAW file is not an image. The image we can see on the camera's LCD screen, or when we open that file in a RAW editing program, is a JPG version of the captured image. Therefore, a postprocessing with a specific RAW editing software is necessary, and precisely for this reason it is known as digital negative.
RAW files generally consist of three main parts: the actual RAW data of the image sensor, a JPG preview processed by the camera, plus all relevant header and metadata information incorporated.
RAW is thus a proprietary file format, linked to a specific camera model: the Canon RAW file extension is .CR2, Nikon is .NEF, Olympus is .ORF, Sony is .ARW, etc.
Also, most brands have their own RAW editing software, which is usually offered with the camera itself:
- Canon: Digital Photo Professional
- Nikon: View NX2 and Capture NX-D
- Olympus: Olympus Viewer
- Panasonic / Pentax: SILKYPI
- Sony: RAW Viewer
The most popular and used third-party RAW editors are: Adobe Lightroom, Adobe Camera Raw (ACR) and Capture One Pro, among others.
When we chose shooting in RAW format, the camera does not apply any algorithm on the information obtained, this means that with this file we retain even the smallest detail that our sensor has managed to capture. RAW files have as an appendix (tags) the settings that the camera had at the time of shooting.
RAW is neutral and is made up of digital values for each pixel. The light that reaches each pixel becomes an electric charge that lastly is converted into a digital value. The, more light is received the higher value is obtained. Each pixel captures only a color component following a pattern that repeats itself.
The previous figure shows how image data is captured on a digital camera. The sensor is a set of "photo-sites". A "photo-site" consists of a photodetector, which is essentially a photon counter, under a "red", "green" or "blue" filter. After an exposure, the photon count in each photo-site is performed as an analog voltage. This voltage is read from the array of sensors row by row in a raster sequence.
The signal is sampled for each photo-site response and converted in digital words using an analog to digital converter (ADC). It is these digitized samples at the ADC are the sensor’s raw image data.
The image also indicates that the camera’s ISO setting is an analog amplifier prior to the ADC. Increasing the amplification, for higher ISO, amplifies low level signals but at the cost of also amplifying sensor noise.
Each pixel in the RAW file has a single color component, R, G or B, not all three. Obtaining the other two color components for each pixel and also having the correct RGB value is the objective of RAW postprocessing, which is carried out in several basic stages.
RAW editing is carried out through a processor (DSP-Digital Signal Processor) and consists of several processes:
- The demosaicing.
The task of estimating the two missing color components in each pixel is called demosaicing. It consists of a chromatic interpolation algorithm and is is a digital image process used to reconstruct a full color image from the incomplete color samples output from an image sensor overlaid with a color filter array (CFA). It is also known as CFA interpolation or color reconstruction. Most digital cameras acquire image color information using a single sensor, which is covered with a mosaic of filters that separate light into three components, usually Red Green and Blue (Bayer Mosaic). The chromatic interpolation allows to obtain the corresponding color information for each pixel.
- Gamma correction.
It consists of a corrective factor that defines the relationship between a pixel's numerical value and its actual luminance. Without gamma, shades captured by digital cameras wouldn't appear as they did to our eyes (on a standard monitor), because our eyes do not perceive light as the cameras do.
- The color space conversion.
This involves the conversion of RGB values from the RAW image to a standard RGB color space appropriate to the display device. This step uses the camera's white balance settings.
- Custom image control settings and image modes (Picture Control & Settings).
Contrast, brightness, saturation, hue, focus, etc. As well as any preconfigured shooting mode of each camera model (vivid, portrait, landscape, monochrome, binary, etc.).
- JPG compression.
The camera always produces a JPG even if shooting in RAW mode only. The preview on the LCD screen after any camera shot is a JPG, produced after all the processes described above. When we capture a scene in JPG, the camera is generating a provisional RAW file, which immediately processes, adjusting the color, tone and sharpness, and then compresses, discarding a lot of information and converting it into an 8-bit JPG file per channel that is saved on the memory card.
Therefore, it must be taken into account that almost any digital camera always shoots in RAW mode and that, if we choose to save the image as JPG, we are delegating the conversion from RAW to JPG to the software incorporated in the camera.
The JPG format is a lossy compression format, which means that when our camera saves the photo in JPG, it automatically applies a series of "destructive" settings such as contrast, saturation, white balance, sharpness, etc. (they are applied to the image without the possibility of recovering it without these adjustments).
On the other hand, in the RAW format these adjustments are not applied, but all the information is stored in the file and we are who decide how to apply them when editing the photograph under our own way. That is why it will always be much more advisable to shoot in RAW if you intend to edit your photographs, as you can adjust them to the desired value according to your preferences or postprocessing target.
The question is therefore to decide if you want to make the conversion from RAW format on the camera itself, or later by your PC, assuming the advantages or limitations that one or the other entails. Shooting in JPG, several of the main aspects of the image quality are irreversibly compromised, such as white balance, general contrast, color saturation, or specially having only 16 bits instead of 8 bits when working on shadows or image brightness.
For some photographers, speed and ease of use is capital. But for others, who wish to obtain the highest possible quality without losing information on their original image or wish in the future to prove the image authenticity, they will always consider shooting in RAW.
Only through the knowledge and understanding of the construction process of an image, it can be well concluded that RAW availability is the only way of proving authenticity of an image, assuming we can measure and quantify the processing values decided on camera (pre-processing by custom settings) or off-camera (PC post-production) from the neutral state that RAW entails.
It must be considered that the possibilities of editing or processing existing today in the camera itself, with respect to the original or neutral RAW, are as wide as by means of postproduction software outside the camera.
Going further on the point about where the processing or editing of an image is located, D. David Campbell in the research for World Press Photo collected in his work "THE INTEGRITY OF THE IMAGE" cites the following:
- The difference is the location of the processing: JPG processing is performed in camera following the algorithms of the manufacturer (or complemented by the photographer), while the conversion and processing of the RAW is carried out outside the camera under control of the photographer.
- The assumption that we can have an original image from camera, which can be considered an authentic original image, is not sustainable.
We do not say anything not real if we affirm that the main target of the processing algorithms installed in camera to obtain JPG files, is to impress the owner of the camera. Manufacturers adjust the parameters to get as striking photographs as possible. Therefore, the processing values entered are usually high to achieve that saturation and sharpness that we see on the LCD screen.
In this way, a verifiable fact in the most recent camera models introduced by most manufacturers, is that we can find many more options of “camera profiles” (Picture Style or Picture Control), being much more aggressive in the final result produced, with respect to the neutrality of the RAW from which they emanate. It could be perhaps that manufacturers of SLR cameras or modern mirrorless, pretend not to lose the race in offering the user "bright" in-camera JPG photographs, emulating any "App" with "bright" psychedelic filters that produce no less "bright" photographs from our mobile phones.
See a clarifying example of what we are talking about. A picture taken by “RAW + JPG” shooting option on a Nikon Z7, using the “binary” mode as the “Picture Control” option or camera preset selected.
The result of the JPG produced in camera is as follows,
Although the view of the neutral image of the same scene that RAW shows us is the following,