Colour rgb and cmyk

[Lukas28225412phc4]

Hello,

my question is: 

why is rgb and cmyk not aligned?

if rgb is 0/0/0 cmyk has to be 0/0/0/100.

best regards, Lukas

 

[kevin stohlmeyer · Accepted solution]

RGB 000 is not 100% flat black. When converted it becomes what we call "Rich Black" which is a mix of CMYK.

If you really want to understand color conversions going from one color space to another, this article will give you some insights.

https://www.printingcenterusa.com/blog/how-to-convert-rgb-to-cmyk/

[D Fosse · Accepted solution]

CMYK is not an ideal synthetic color space. CMYK is always based on a real world printing process - an offset press calibrated to a certain standard, using certain inks on certain paper stock. Each CMYK profile describes a specific print process.

CMYK is where the rubber hits the tarmac, so to speak. It's limited by the physical characteristics of real ink on real paper.

The black ink (K) is very far from black on its own. Usually it's rather charcoal gray, so a 4 color mix will give a deeper black. But you can't just dial all four inks up to max - that would smear and not dry properly on a real press. So there's an absolute ink limit built into all CMYK profiles. This is usually somewhere between 250-330% depending on the process.

[Mylenium]

Understand Photoshop color management

Mylenium

[NB, colourmanagement net]

@Lukas28225412phc4 the relationship between RGB and CMYK that you see there in the screenshot is decided using a calculkation between the document profile and the default ICC profile options and rendering intent in 'color settings'.

So, the value predicted for a conversion from RGB 0,0,0 [in the current RGB coloruspace] to that specific ICC CMYK profile  is 91,79,62,97.

The way black is calculated and printed is set up within the CMYK ICC profile's "black generation"options [during profile creation]. Generally this uses GCR [grey component replacement, where a proportion of the neutral component of any source colour is printed with black ink.].

It would be VERY rare to see a CMYK profile in use where RGB 0,0,0 = CMYK 0,0,0,100

I hope this helps
neil barstow, colourmanagement net - adobe forum volunteer - co-author: 'getting colour right'
google me "neil barstow colourmanagement" for lots of free articles on colour management