The realities of working with images for web vs. print

Often colleagues send me an articles. A lot of times I find them to sound interesting while spreading misinformation. Rarely intentionally, it's much more often that information is left out that the author either thinks is not important or perhaps doesn't know. An articleI read today, "K is the new black" is a good example.
 

It's an interesting article explaining why color of images can be so inconsistent. However the author makes a bunch of assumptions that are probably too often true on the web but tackles why that creates a problem rather than why it happened in the first place. The article is well written and researched and I don't question the information. I also don't know whether the author knows what I'm about to say and chose to discuss the next level deeper or doesn't know it. 

What's important is that for 99%+ people (including most visual professionals) what he is saying doesn't matter if you read what I say here.

JPEG in CMYK
It's absurd and shouldn't be done without very strong and known reasons for it. CMYK is for printing ink on paper - start with white, add color till you get what you want. RGB is for generating light such as computer monitors, tvs, projectors etc. Start with black, add color till you get to white. His whole article started with ignoring that fact. So, given that, JPEG was designed as a lossy compressed format for serving visual imagery over data connections quickly. It's quite easily replaced by PNG-24, but for whatever reason that hasn't really caught on - finally starting to. That said, while JPEG supports RGB and CMYK, it was designed for digital use (i.e. light) and therefore optimized for RGB. If you're printing an image you want CMYK, you don't want loss, you don't need compression.... thus there's no reason to use JPEG either. IF your original image is in CMYK (print) and you need it in RGB, (display), or it's in RGB (display) and you need it in CMYK (print), you need to convert it. Moreover you should never convert directly from one to the other - it's not just that one color space is smaller than the other, each have ranges that aren't covered by the other so both directions lose color fidelity. The only way to do a decent conversion is to have an intermediate step that covers both ranges compleltely - the best known and supported one being LAB. You end up with CMYK-LAB-RGB or RGB-LAB-CMYK - and even still you will need to do color adjustment after, by channel. Ugh people so underestimate the required knowledge for working with this stuff. Anyway, I'm never going to display a JPEG on my site in CMYK, and I'm never going to print an RGB JPEG (it will probably be a CMYK TIFF). Some day our cameras/computers/etc will probably use a format that gives the best of both worlds, but until that happens, this is the world that discerning visual professionals use, and for the rest that article is probably quite accurate - but the real reason why is that there is built-in software trying to make decisions for you and somewhere there's a programmer finding the best common demoninator for making those decisions, not that the system is flawed.

So?
If you're a normal person taking photos and posting them on facebook and printing some of them out, none of this matters - it will probably look good enough. If, on the other hand, color accuracy and quality are important, then using the right formats - not only in color space (RGB/CMYK) but also in file format (JPEG,TIFF,etc) will either solve your problems or make it very easy to solve them in nearly all cases. Any time you need to convert - and it will happen - there is a chance you'll run across a situation where the color is just wrong and you'll have to work to get it as good as possible. 

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