A printing works spends its day opening files it has to ask questions about: does the colour reach a little past the line the blade will follow, where exactly is that line, are the colours stated in the inks a press lays down or in the colours of a screen. This sheet answers all of it before anybody writes back. The paper is deliberately larger than the finished page: 472 by 692 typographic points of sheet for a finished page of 400 by 620. Thirty-six of those points stand on each side, nine of them for the colour to run past the cut and the rest so the trim marks have room outside it. The page names all three: the paper, how far the colour runs past the cut, and the cut itself.
It also prints what the file says about itself: the name of the job, the profile of the device it is stated for, and a yes or no on trapping — the hair's breadth of overlap given to two touching colours so that a sheet moving slightly on the press opens no white line between them. The claim to the print standard is yours to complete, and it takes one thing. PDF/X-4 rests on the colour profile of the press the job was separated for, which is the one piece only your own printing works can hand you: give the engine that profile and this very same sheet claims PDF/X-4. Left to itself the library builds a profile describing a screen, which is the right description for a document read on one. Either way, the profile travelling inside your document is the one you chose, and it is the only one in there.
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.
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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.
Two inks the press carries on a plate of their own, each at ten strengths, a piece of work set in both, and the alignment crosses used to line the plates up — drawn in an ink every plate answers to.
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.
