I've often been frustrated when I see some of my photos, that I have become accustomed to viewing on a monitor, in printed format. This is because of the RGB to CMYK conversion. I'm thinking about this now as it relates to my upcoming book, CREATIONS, and as I've been working with literally hundreds of images.
The above awesome graphic illustrates the difference between RGB, which is how we see images on a computer screen, and CMYK, which is how we typically see images in print.
RGB, which stands for Red, Green, Blue, is a broader spectrum than CMYK, which stands for Cyan, Magenta, Yellow, and Black. In regard to printing, CMYK is also called 4 Color. The above graphic illustrates how much narrower the CMYK spectrum is than the RGB spectrum.
Most printing, whether digital or offset, is 4 color, or CMYK. Very high-end and/or custom printing offers CMYK + light cyan and light magenta, and possibly more, or CMYK + a spot color—whatever a customer is willing to pay for. Coca-Cola Red and IBM Blue, for example, are CMYK + a spot color, when in print.
Where the RGB/CMYK difference is most visible to me is in very vibrant blues with some violet. However, it is primarily noticeable in a relative sense: I notice it because I have seen the RGB representation, and I am aware of what is being lost relative to what I see on screen and with my own eyes.