A two-colour job costs less than a four-colour one and the colour comes out exactly right rather than nearly right, which is why so much stationery, packaging and signage is printed that way. It works when the file names the spot colour it wants, so the printing works knows which plate those marks belong on, and says how much of that ink goes down as a single figure.
Where that ink does not exist — on a screen, or on a press that does not carry it — something still has to be shown, so the file carries beside each ink a stand-in made of the ordinary four. That is what you are looking at above, and it is why the sample here can be looked at on a screen at all. The alignment crosses are drawn in an ink every plate answers to, so they come out on all of them: that is what lets the printer lay the plates exactly over one another.
Nothing is left out and nothing is simplified: this is the program exactly as it runs, for the developer who uses this library. The third is the description itself: a plain list of what the page has to say, which is what the service is sent.
Read the Rust source Read the Python source Read the JSON source
Swatches in each of the three ways to say a colour — a grey as one number, a screen colour as three, a printing colour as four inks — each captioned with the instruction actually written into the file, and one mid-grey said three ways.
The same six colours said as bare numbers and then read through the screen profile the file carries, plus a ramp from light to dark and a sweep of measured hues: colour that still means the same thing on another screen and on a press.
Eight choices of plate among the four usual inks, each with the small program that shows it printed underneath, and two inks the press carries itself used together, every strength of one against every strength of the other.
A chart of house colours the file carries, and a drawing whose sixteen numbers are places in that chart rather than colours. The same drawing is shown twice through two charts: repainting a whole brand is one chart, not every drawing.
One pattern that states no colour of its own, laid down in five colours and in five strengths of one press ink: the fill says what colour to lay it down in. Beside them, the same hatch made of patterns that carry their own colours, which is one pattern per colour.
One drawing on three pages: a press sheet stating where the ink runs, where the blade falls and what is worth keeping, with trim marks; the same sheet cropped to the finished page; and a landscape page that states a quarter turn clockwise on an upright sheet.
