Press and Prepress Equipment

Measurement of printed jobs and of proofs has never been more important than today. Reliable and easy to understand information is at the forefront of modern process control.

Measuring colour in the press-room and on proofs
The ability to reliably measure colour as well as tone is a necessity since standard colour is, nowadays, specified as an L*a*b* number.
It is not possible to specify on-press colour as density since achieved colour depends greatly on many factors, including ink, paper and fount solution.

Press-side diagnostics
In the press-room, accurate diagnostic equipment is of utmost importance if standards are to be maintained. If the press is to be run to numbers then the densitometer or spectrophotometer used at press-side to assess the printed sheet must be known to be accurate and well maintained as well as being regularly calibrated.

Checking plates
It is imperative that when plates are checked (and they ideally need regular checking), that checking is done with a video plate reader. Density based plate readings are not quite accurate enough.

Process Control on press
It is possible to control press output using only solid ink density and two *TVI readings, perhaps at 40 and 80 percent as specified in the ISO standard. However, if the press misbehaves only in areas outside two commonly monitored TVI areas, printed work can still suffer and the printer’s job in matching proofs and maintaining grey neutrality can be much more difficult, so that Make-Ready time is increased.
This means that monitoring carried out using a simple densitometer, which cannot practically give a picture of TVI nor any indication as to achieved colour is only part of the process control job.
*the term TVI, for Tonal Value Increase is now the accepted term for what was known as Dot–Gain.

MetaPrintCheck:

MPC, an application for intuitive and comprehensive analysis of press and proof data.
We use, supply and recommend MetaPrintCheck (MPC), a diagnostic application which allows monitoring of solid printed colour and TVI throughout the tonal range as well as greybalance. (TVI tolerances for just 2 points: 40 & 80 percent are specified in the ISO 12647-2: 2004 standard). MPC can be used to assess printed output to allow printer / press minder and pre press operator to not only keep tabs on day to day performance but also to adapt plate curves and running weights for new paper stocks.
In summary, the MetaPrintCheck report allows the operators to assess colour and tone in an intuitive way and also provides the detailed data needed for CtP adaptation (adaptation of plate curves in order to bring press output to ISO standard, or to keep it on standard). In addition, MPC provides for assessment of incoming or house proofs including the option for comparison of measurements from proofs and from printed jobs.

Maintaining a press condition day to day to within the tolerances of an internationally applicable standard (e.g. the ISO 12647-2: 2004 standard) is much simplified when running process control via MetaPrintCheck, since the report includes information to make assessment of needed changes far simpler than looking at ΔE and L*a*b* data directly on a spectrophotometer.

The use of colourmanagement and the application of practical working standards ensure predictable, reproducible colour results and thus permit the seamless harmonisation of pre-press and printing operations. In addition, increasing numbers of customers are coming to appreciate the value of having colorimetric evidence that colour proofs and production runs correspond to internationally applicable standards. MetaPrintCheck provides you with an easy-to-use software product based on Microsoft Excel® with which you can perform the quality assurance of print runs and proofs.
In just three steps – print, measure, assess – you obtain a detailed numeric and graphical evaluation that not only serves for quality control purposes but also significantly simplifies process control operations at the printing machine and during the production of printing formes thanks to the graphical presentation of important parameters.

More detail on MetaPrintCheck.
the 4 report pages:

MetaPrintCheck’s 1: print analysis and 2: CtP adaptation report. (more detail below)

MetaPrintCheck evaluations not only allow you to check that all standards and tolerances are adhered to, but also provide you with additional information to help you optimise your proof and printing results. The first page is for colour, greybalance and overall TVI analysis, the second looks at TVI in a more detailed way. Generally, on a day to day basis, if page 1 looks good, no other page need be inspected.

With the addition to a job of a practical and freely available target like the ECI greyCon strip shown here, MPC analyses printed colour (and compares this against a solid colour (L*a*b*) reference, either from the ISO Standard or from other published industry accepted reference sources) for a particular printing condition of paper type and printing method. Also analysed from this same strip are TVI and Density and greybalance.

MetaPrintCheck’s 3: Proof Analysis and 4: greybalance (in detail) report sheets.

MPC: Production Printing, Process Control:

During the process control of a production print run, the printer can only significantly influence the colour result by modifying the quantities of the individual inks.
However, changing the ink quantity not only affects the colour in question, but also modifies TVI. When deciding whether the ink quantity corresponding to a printing colour needs to be increased or decreased, the printer must, therefore, always take both these parameters into consideration.

MetaPrintCheck presents the deviation of the colour co-ordinates and tone value increase in such a way that the printer can quickly recognise whether it is necessary to increase or decrease the ink quantity for the corresponding colour.

MPC: colour difference in ΔE, L*a*b*, interpretation:

In itself, the much quoted colour difference “Delta E” does not provide much information. For this reason, the comparison of the aim and achieved values provides you with other, highly informative parameters allowing you to evaluate your printed products and proofs:

Whether greener or redder, yellower or bluer – the figures displayed against coloured backgrounds indicate the colour deviations referred to by the values Δa* and Δb*.

For the purposes of checking production runs, the international standard ISO 12647-2:2004 specifies an upper limit for the hue difference ΔH* between any sheet in the production run and the OK print. MetaPrintCheck permits this check of the hue difference ΔH* – simply load the measurement values of the OK print as the reference – MetaPrintCheck will provide you with an idea of the direction in which the measured colours deviate from the standard values, lighter or darker (ΔL*), duller or brighter (ΔC*). The hue angle (Δh*) is a good tool for assessing colour casts in grey colours.

MPC: Inking indicators:

ΔL*, ΔC*, ΔH*
The bars labeled with “ΔL*” for Lightness, “ΔC*” for Chroma (saturation) and “ΔH*” for Hue indicate the corresponding deviations (Δ, pronounced “Delta”) of the actual values from the aim values. These bar charts are based on the depiction of solid colour densities (colouring) familiar from printing machine control mechanisms in order to simplify the unfamiliar use of L*a*b* colour values for printers.

colour control and ∆L* and ∆C*
Bars descending from the ‘0’ line indicate under–inking of the colour in question. If both bars ascend then the colour is slightly over–inked. If a colour is already slightly darker but is still insufficiently saturated (or vice versa) then further optimisation of the inking for the colour is not possible.

colour control and ΔH*
Unlike in the case of lightness and saturation, the printer can barely influence the hue difference ∆H* by changing the inking. As a result, a high deviation in the ∆H* graph means that the nominal colour co–ordinates cannot be achieved using the ink in question (here cyan).

MPC: Tone value increase curves:

On page 1 of the report, two graphs contain the tone value increase curves which indicate not only the measured tone value increase values but also the nominal (aim) curve (dashed/dotted line) and the upper and lower limits for the permitted tolerance (dotted lines).

The nominal (aim) curves for black or for cyan, magenta and yellow correspond to the defaults for any selected reference and are dependent on the printing process, the paper type, the plate type (positive or negative-acting) and possibly also the screen ruling. When evaluating spot colours, MetaPrintCheck uses the nominal (aim) values for black.

MPC: Spread:

To prevent a colour cast, the tone value increase curves for cyan, magenta and yellow must not deviate too much from one another. Spread refers to the tone value difference between the inks with the greatest and least tone value increase. Usually, it is assumed that the curves are regular and, for the sake of simplicity, the spread is measured at 40%. However, this tolerance can also be individually modified.

MPC: Solid density:

Once assessed for a particular ink/paper combination, density values remain a valuable dimension for process control during production runs. Consequently, MetaPrintCheck outputs the solid density of the process and spot colours if the measurement data contains spectral values or density values

MPC: Ink trapping:

Ink trapping and reduction greatly influence the colour result. Thus the impression made by a blue tone depends not least on how well magenta is trapped by the previously printed colour cyan. colour trapping also has a great impact on the greybalance of darker grey tones since the printing inks are then increasingly overprinted and rarely printed adjacently as in the case of lighter grey tones.
MetaPrintCheck specifies ink trapping in accordance with Preucil in order to permit an objective comparison with other printing results and provide manufacturers of printing inks with a basis for possible changes to the compositions of their inks. If the printed result was not created using the standard ink sequence “KCMY” then you can set the modified colour sequence in a pop-up window to ensure the correct calculation of ink trapping.

MPC: Chromatic grey and greybalance:

The combination printing of cyan, magenta and yellow has a great effect on the colour result–in particular the reproduction of grey tones. The evaluation of chromatic grey (CMY-grey) patches is therefore becoming increasingly important for process control during printing.
Before special greybalance control wedges can be evaluated, the CMY–grey and K only grey patches must be identified in the measurement data. Corresponding control files for measuring with the GretagMacbeth MeasureTool are supplied with the product. The CMY–grey patches of the “Ugra/FOGRA Media Wedge CMYK” are automatically recognised on the basis of the CMYK colour values. Instructions are provided for use with the graphs above, which are intended to help printers correct any colour cast that may be present by modifying the inking while also taking account of the overall coverage.

MPC: CtP, calculating compensation curves:

The printing inks are displayed separately, as well as in combination, in order to simplify the adaptation of the TVI curves during plate production. The deviation graphs (above right) simplify identification of the required corrections of each tone value curve.

MPC: Assessing Proof Quality:

It has been said that “There is no proof without an Ugra/FOGRA MediaWedge”. That is a pretty strong statement, but if a proof purports to represent press potential (and we believe that it must), then that must be able to be proven. The addition of an internationally standardised control wedge, e.g. an Ugra/FOGRA MediaWedge, to any proof allows a user to read the strip into diagnostic software and assess proof accuracy.

Talk to us about software for proof evaluation, we use color-solutions’ basICColour Control or MetaPrintCheck depending upon application.