When we talk about RGB and CMYK, we often hear that the first concerns the digital world and the second concerns printing. But this is a simplification that risks being misleading.
Actually, for a computer, 'print' means any type of visible output: a sheet of paper, a screen, a projection, even a traditional photographic print.
It is therefore not the type of support that determines the difference, but the way in which the color is generated.
In fact, the real distinction between RGB and CMYK stems from two opposing physical principles: additive synthesis And the subtractive synthesis.
RGB — Red, Green, Blue — works with light: it starts from black, that is, from the absence of emission, and adding it up to white. This is the principle that monitors, projectors, smartphones use.
CMYK — Cyan, Magenta, Yellow and Key (black) — works by subtraction: it starts from a white surface that reflects all the light and subtracts portions of the light spectrum through the inks. The more ink is superimposed, the less light is reflected, and as a result you get to black.
It is often thought that printing always means conversion to four-color CMYK, but this is not the case. Are there processes of RGB chromogenic printing Like the LightJet And the Lambda, where the digital RGB image is transferred to photosensitive paper using red, green and blue lasers. Here you work exactly like on a monitor: with light. No four-color conversion, no color subtraction. In these cases, color management must respect specific profiles, but it basically remains a “luminous print”, even on physical support.
This distinction has enormous practical implications, starting with the concept of White. In RGB, white is obtained by illuminating all channels (255, 255, 255) to the maximum, while in CMYK, white is not created: it is the support itself. It is the paper, or the base material, that provides the white, and this is why the quality of the support is crucial in traditional printing. A coated paper will return a brighter white than a matte or natural paper. On the screen, on the other hand, we can obtain a perfect white simply by calibrating the light source correctly.
But that's not the only difference. The two methods are also based on a different analysis of the values of the individual colors: additive synthesis allows 256 levels of control for each individual color, while subtractive synthesis allows a variation of color density from 0 to 100%. In practice, a full red color will be similar to RGB (255,0,0) and CMYK (0,100,100,0), this difference in calculation is implicit in the different working system of the two color methods.
Even the color depth so it changes radically. In RGB, we work with millions or billions of colors, taking advantage of large color spaces such as sRGB, AdobeRGB or ProPhotoRGB. In CMYK, the range of colors is narrower: some very bright greens, some electric blues, or intense oranges simply cannot be reproduced with traditional inks. And not only that: each printing process has its own actual color space, dependent on paper, inks and printing technology.
However, what is often ignored is the role of the “Key”, or black in CMYK. Black is not only used to darken the image: it allows you to give structure, depth and purity to dark tones, avoiding obtaining “muddy” blacks from the sum of cyan, magenta and yellow. It is the Key that allows the finer details to be kept sharp, giving stability to contrasts on printed paper.
Precisely because of these differences, there are situations in which, even if an image will be displayed on RGB screens, it is essential to treat it thinking in CMYK. An emblematic example is given by the historic photographs of National Geographic. The aesthetics of the reportages were built considering the four-color rendering: warm tones, compact shadows, colors calibrated for printed paper and a strong black structure that defined contrasts and textures. To maintain visual consistency and respect that stylistic identity, the images must therefore be managed and corrected with CMYK printing in mind from the beginning, even if they were used only on a monitor or for the web.
Understanding the difference between additive synthesis and subtractive synthesis also means understanding how visual languages change: in RGB it is easy to obtain bright and luminous whites because light is added, while in CMYK it is necessary to “protect” the white of the support, avoiding contaminating it. Conversely, for blacks, it is CMYK printing that allows obtaining fuller and deeper tones thanks to the specific black ink, while in RGB devices, black depends on the device's ability to block light emission.
Ultimately, RGB and CMYK aren't just different technologies: they represent two completely different ways of constructing color perception. Those who work seriously with images - whether a photographer, graphic designer or digital artist - must know how to predict how color will behave on the final medium. Because an image is not only made of pixels or dots of printing: it is made of light, matter, and how the human eye interprets the interaction between the two.
Leica Q (Typ 116) - Profile comparison
Sometimes a picture is worth a thousand words. On the left, a photograph taken in an environment with obvious lighting complexities, developed with the Adobe Color profile; on the right, the same image, but with the TheSpack profile. For this comparison, second-generation profiles were used, optimized in 2021, so they are still far from subsequent progress. This image is particularly critical because of a nuance in saturation, which, if not properly normalized, generates irregularities. Often, the result obtained with the Adobe profile leads to a negative judgment on the quality of the file and the camera itself. While using a similar tonal curve for contrast, the TheSpack profile produced a much better result. There is greater chromatic consistency, extension of detail and legibility in all areas of the image. Noise and granularity, evident with Adobe, have been reduced thanks to the structure of the TheSpack profile, designed to correctly balance the output channels. This limit in Adobe profiles often causes a drop in quality that is wrongly attributed to the technical medium. The best detail, superior tonal rendering and the absence of irregularities are not the result of post-production corrections, but of a carefully studied and developed color profile.
Panasonic S1R - Imperceptible defects
We are often used to looking at the whole of an image, losing sight of the detail that defines it. This reflection, in itself, might seem out of place, considering that photography is based on visual perception, on the impact that a subject, light, interpretation and dynamics of a scene transmit to us. It would therefore be natural not to focus on the details. And yet, here comes a great paradox: we invest in expensive lenses, glorifying their performance. We try to correct aberrations, chase resolution, apply textures and contrast masks to emphasize details, and yet we often forget one fundamental element: the color profile, which can destroy all this work. Now looking at the enlarged detail of a photograph developed with the Adobe Color color profile and the same image with TheSpack. The choice of how to intervene on a color profile, which parameters to consider and how to optimize the rendering of a sensor inevitably leads to consequences that impact the final quality of the image. This can even frustrate the work of engineers and designers who have created the highest quality optics. In the image developed with the Adobe Color profile, the light of a neon is dispersed, leaving an obvious halo around the light source. This phenomenon reduces texture in highlights, compromising texture and detail, and altering the overall quality of the photo. A small defect that, however, has a heavy impact on the performance of the lenses and is manifested throughout the image, regardless of the lighting conditions. Obviously, this consideration stems from the fact that a color profile can be generated taking into account different parameters, including those that determine the variation of hue and saturation as the brightness changes. For this reason, we have chosen to divide our system to make it effective in a wide range of situations. We have implemented specific solutions for each individual camera, so as to obtain impeccable results, regardless of the shooting conditions. This approach allows us to guarantee a consistent and accurate color rendering, minimizing deviations that may compromise image quality.
