About This Site

Why this site exists #

There is no shortage of colour converters. Most of them give you a number and nothing else, which is fine until the number does not do what you expected — and with print colour, it very often does not.

So every converter here shows the formula it used, works through one example by hand, and says plainly what that formula gets wrong. The RGB to CMYK arithmetic, for instance, quietly assumes that ink behaves like a perfect filter. It does not, and knowing that is more useful than another decimal place.

How the conversions are calculated #

All of the conversion functions were written from scratch for this site, from the published mathematical relationships between the colour models. No third-party colour library is used. The formulas are printed on the relevant converter pages so you can check the working or implement it yourself.

Everything runs in your browser. No colour you enter is transmitted to us, logged, or stored anywhere.

What this site does not do #

• It does not replace a colour-managed workflow. If you know which press is running your job, your design software with the correct profile will always beat generic arithmetic.
• It does not replace a physical proof. Nothing on a screen can.
• It does not publish licensed colour data. Proprietary colour systems belong to the companies that maintain them, and we do not reproduce their libraries.

How pages get published here #

Colour converters are easy to mass-produce and most of them are. The approach here is deliberately slower, and it comes down to four rules:

• Show the working. Every converter prints the formula it applied and works one example through by hand, so you can check the result rather than trust it.
• Name the limits. Each page says what its formula gets wrong. The arithmetic behind RGB to CMYK assumes ink behaves like a perfect filter, and it does not — that is more useful to know than another decimal place.
• Test the maths. The conversion functions are checked against known values, and every combination is swept for out-of-range or undefined results before a tool goes live.
• Publish when it is finished. Pages go up in small batches once they can be written properly. Several conversions are deliberately still missing rather than shipped as thin calculators.

Corrections #

If you find an error in a formula, a worked example or a table, email contact@hex-cmyk.com. Formula errors take priority over everything else, because a wrong number here could end up on a press. Corrections are made and the review date at the foot of the page is updated so you can see when it was last checked.