RGB vs CMYK

RGB and CMYK are the most common methods of reproducing colour in today’s modern media. 

An explanation of RGB

RGB stands for ‘red, green and blue’. It is the method used to reproduce colour on back lit displays. Examples would be a television, a computer monitor, an iPad or smartphone. When viewed up close, it is possible to see individual pixels, each made of three vertical bars; red, green and blue (fig.1). All colours shown on these types of devices are created by independently altering the luminance of the three bars found within each pixel. When viewed at a normal distance, each pixel is so small that the human perceives the pixels as one complete colour (fig.2).

An explanation of CMYK

CMYK stands for ‘cyan, magenta, yellow and black’. Combinations of these four colours are used in professional full colour printing for items like brochures, leaflets, newspapers and packaging. Colours are reproduced by mixing percentages of cyan, magenta, yellow and black ink (fig.3). For more complicated artwork, like a photograph, the image is separated ino the component CMYK levels and print plates are made for each colour (fig.4). Cyan, magenta, yellow and black inks are then applied to the media, one at a time, using these print plates. When combined, a full colour image is created.

Limitations

The most significant difference between RGB and CMYK is the range of colours that each can produce. Displays that reproduce colour using RGB rely on brightness and luminescence to show the graphics. For this reason its possible to generate brighter, more vivid colours than can be achieved using the CMYK method. The colour wheels below show an approximation of the gamut of colours achievable by each method. 

Occasionally an image that has been created for an RGB display will need to be printed using the CMYK system. To do this the image needs to be converted from the RGB colour scale to the CMYK colour scale. If the RGB image contains a lot of very vivid hues, converting to CMYK will result in a dulling down of colours. Software used to make such conversions, like Adobe Photoshop, substitute the RGB colour for its closest CMYK equivalent. The difference can be dramatic or completely indistinguishable, depending on whether or not the original RGB image contains lots of bright colours that fall outside the CMYK colour gamut. 

Conclusion

RGB vs CMYK is not actually a choice. The two are completely different methods of reproducing colour on completely different media. RGB is only applicable when showing images on back lit displays, like computers and televisions. CMYK is only applicable for conventional printed media. There can be a sense of disappointment when a client sends us an RGB image with vivid colouration and wants us to print it on a business card or other paper based media. We employ the best software available to us for converting between the two formats and always do our utmost to get as close to the original image as we can. However, even with the most advanced equipment, it is not possible to print the more luminous shades found in some RGB images using the CMYK system.