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Knowledge base

RIP and print strategy: preparing a file so the machine can print it well

By Piotr Jędrzejczyk, AssembleX Industrial Services

The RIP is where a design becomes dots. Resolution, screening, ink limits and colour conversion are decided there, and they shape the print long before the first drop is fired.

What a RIP does

The RIP takes the customer's file and turns it into the data the heads can print. It converts the colours through the machine profile, splits them into ink channels, applies the ink limits and the linearisation curves, reduces the image to dots or grey levels at the machine resolution, and delivers the result to the heads in step with the transport.

Each of these steps is a setting, and each can ruin a good file or rescue a mediocre one. The settings that matter most are the resolution, the screening, the ink limits and the print strategy.

Resolution

The print resolution is chosen for the job: higher gives finer detail and costs data and, depending on the system, speed. The file resolution at the final size has to match it. A low-resolution file stretched to the size of a slab does not gain detail; it gains soft, stair-stepped edges (Figure 1).

Figure 1. The same curved edge at three resolutions. Left: too low for the job, the edge steps. Right: enough resolution, the edge is smooth.
Figure 1. The same curved edge at three resolutions. Left: too low for the job, the edge steps. Right: enough resolution, the edge is smooth.

Screening

Screening decides how tones are turned into dots. Regular, ordered patterns can create visible textures or moiré on large smooth surfaces, and they can interact with the structure of the substrate. Stochastic, frequency-modulated screens scatter the dots irregularly, which hides patterns and also helps to hide small stitching errors. The choice depends on the product and on how smooth the surface has to look.

Colour conversion and ink limits

The colours of the file are converted with the machine profile and a chosen rendering intent. Then the ink limits are applied, per channel and in total (Figure 2). Too much ink floods the surface, merges the colours, dries or cures badly and makes the process unstable. On ceramics the amount of pigment also decides the colour after firing, so the limits come from firing tests, not from the screen.

Figure 2. Ink laydown of four colour channels stacked for one tone. The dashed line is the total ink limit. The left stack exceeds it and would flood; the right stack is the same colour with the ink reduced below the limit.
Figure 2. Ink laydown of four colour channels stacked for one tone. The dashed line is the total ink limit. The left stack exceeds it and would flood; the right stack is the same colour with the ink reduced below the limit.

Print strategy

The print strategy is how the job is built on the machine: single-pass or multi-pass, the number of layers and their order (base, colour, effect, varnish), the print direction, how the image is cut and tiled across the heads, and the offsets that register the colours to each other. The strategy has to be planned with the substrate and the process in mind, not only with the image.

Auditing the customer's file

  • Resolution at the final size.
  • Colour mode and the embedded profile.
  • Overprint, transparency and black text.
  • The size of the image against the size of the product, including bleed and repeats.
  • Whether the colours lie inside the printable gamut.

Setting up a new job

  1. Audit the file. Check the resolution, the profile and the colours against the points above.
  2. Choose the print mode and resolution..
  3. Apply the machine profile and the rendering intent..
  4. Set the ink limits, per channel and in total..
  5. Print a test in production conditions, including the firing or curing..
  6. Compare with the reference. Adjust in the RIP only what belongs to the RIP; a machine fault is fixed on the machine.
  7. Save the job as a template, so the next run starts from the same settings..

Common mistakes

  • Stretching a low-resolution file and hoping for the best.
  • Assuming the file is sRGB without checking the embedded profile.
  • Ink limits set too high.
  • Hiding machine faults with RIP settings.
  • No job template, so the settings differ from run to run.

A good RIP setup builds on a stitched, linearised and profiled machine, and it makes the most of it.