Question 4 - What are Colour Profiles and why are they relevant?
This is meant to be a brief basic overview, not an expert analysis. But it is useful to understand these concepts in broad terms if nothing more to get the best result. If you have a great professional printer you won't need to worry so much about the detailreturn to FAQ list
The realities of images as we see them on our devices vs commercial printing reproductions can't be ignored if you want the best results with printing digital images. Commercial Printers were around before we were all staring at screens, and the mediums are obviously very different. Device screens project light through the image to our eyes, whereas the light available to a print usually only comes from the surroundings, unless artificially lit.
The main colour profiles to be discussed differ in what they can reproduce for your eyes. The widest spectrum of colour is available to the human eye itself. As we move to screens and printing a narrower range of colors is available.
On our screens the colours are represented as pixels blended together at on a scale not visible to our eye without magnification, and based on R (red), G (green), and B (blue) - RGB. Even within this spectrum there are different flavours of available colours - ProPhoto RGB, ROMM RGB, Adobe RGB (1998), Apple RGB, RGB, sRGB, and many other proprietary versions of these.
All the colours on our screens are derived from these primary colours of Red, Green, and Blue, which are intensified as they're added together and projected by the back-lighting of our devices.
Printing establishments on the other hand use a different colour profile of CMYK, for Cyan, Magenta, Yellow, and Key (Black). These colours are combined in commercial printing to produce the printed image on the substrate of choice - e.g. paper, newspaper, magazine, metal, glass, acrylic, etc.
Therefore, translating between RGB based colour profiles and CMYK can produce tangible differences and sometimes much duller images, especially if the process isn't a highly professional one. If you've ever designed a business card and they come back completely different in colour and vibrancy, this is likely to be a significant factor. Colours that are within the RGB colour profile but outside of the CMYK colour profile, are considered within CMYK to be out of gamut, and therefore need to be converted in some way (closest match, closest surrounding aggregate of colour, and other approaches).
I think of the colour profiles in this way - my own simple analogy for those unfamiliar with this concept.
If you take the family to the park with a large picnic rug (ProPhoto/ROMM RGB), then to the lake or swimming pool with a large beach towel (RGB), and then to the backyard with a bath towel (CMYK). Each time you'll have less space to spread out and fit everything in. You need to adapt from lots of room for everything, to less. You leave stuff behind each time.
In summary, as you see in magazines, wall prints, and other commercially printed material, CMYK can still accommodate a diverse range of amazing colour and vibrant reproductions, but you have to be involved to make sure you get what you want through the conversion from your digital image to the printed version. And printers around the world will have different approaches and competencies, so you need to do your research and have someone reputable produce your quality print from your high-resolution files
Take a little time and stay involved in the process to help achieve a great result