Calculation of area coverage and consumption quantities in print
As we explained in our first tutorial, you can create high-quality separations of all included colour channels from a cleanly prepared print PDF using a fairly simple workflow.
If you don't know this tutorial yet, you can find it here.
In this second tutorial we would like to show you another important benefit of these separations. You can also use these separations to determine the area coverage per channel almost exactly, which is an enormously important parameter, especially in offer calculation, process planning and ultimately for purchasing.
We know from experience that many designers, media producers and printers often despair of this task. At the very least, the relevant online forums are full of enquiries on this topic and solutions are generally not provided or it is assumed that there are no tools on the market for this task and that the expected material consumption can only be seen in production.
This is nonsense, of course, and that is why we would like to address this topic today and demonstrate a super-simple workflow for determining the area coverage of each individual ink and coating in a production run, as well as calculating the expected consumption in production based on the job-specific production data.
Of course, for this tutorial we will use exactly the same print job as in the first tutorial. In order to make it clear, we will take only one printing form from this job as an example. Since we would like to show later that it is even possible to calculate the amount of pigment required for pigmented coatings, we will use this pigment coating form as an example for this tutorial. At the end, we will calculate the consumption for all materials, but only in a shortened form.
As you remember from our first tutorial, the print job shown was a secondary food packaging produced in offset printing and printed with four printing inks (Magenta, Yellow, Pantone Black 7 C and Pantone 376 C) from Epple and three coatings from WEILBURGER Graphics (a SENOSOFT® WB MATT COATING FP NDC 350210, a SENOLITH® UV GLOSS LACQUER INLINE FP NDC 360424, a SENOLITH® WB GLOSS PRIMER FP NDC 350072 as a carrier coating for the effect pigment Pyrisma® T 30-24 from Merck) and two hot transfer embossings from Kurz.
As announced, we will concentrate for the time being on the pigment coating form, which we still know from our first tutorial:
(Sorry, all desktop screenshots are in German)
Since we have already integrated the coating bars into the form during the pre-press stage, this high-quality separation created beforehand means that we already have a clear image of the coating plate produced and thus of the final coating application.
Here again is the pure separation of this form:
We now open this separation, which is currently still available as a vector-based PDF, in Photoshop (yes, that's right, we misuse Photoshop in our solution for determining the area coverage).
We make sure to open only this one page of the 17-page PDF - in our example this is page 11 - set the Photoshop options in the open dialogue to end format bleed, the colour space to greyscale and the resolution to 300 dpi.
As a result, we now get a greyscale image of the separation with transparencies. Here, all areas that did not contain any information when the PostScript file was ripped for this colour channel are now transparent.
Since we do not want this transparency for the further process, we now first reduce to background level.
As a result, we now get a black and white image of this separation.
Since this is a cleanly worked out lacquer form, this file naturally does not contain any halftones/greyscales, as these would cause considerable problems in lacquer plate production. We recognise this line art when we zoom into the file.
Now let's move on to Dort's hack ;)
In our workflow we use the interpolation qualities of Photoshop to determine the area coverage very precisely.
To do this, we first open the Image Size menu:
Now we deactivate the option "Keep aspect ratio" ...
... and select 1 pixel each for width and height.
This means: We interpolate the complete separation to a single pixel. We make sure that the option "recalculate" is activated and set to "automatic" (except for the option "pixel repetition", any other option would also be allowed for this workflow) and start the interpolation process by clicking on "OK".
After doing so, it looks at first as if the image has completely disappeared. But of course, it has not. It just consists of a single pixel and is therefore very, very small. In order to see and examine this pixel, we zoom in to the highest zoom level (here simply Command 0) and there is our pixel.
Next, we make sure that the info window is open, select the pipette and set its recording area to 1 pixel.
Then, by placing the pipette over the pixel, we measure out the grey value of our just interpolated pixel.
In the info window we can read this grey value. In our example it is a grey value of 12 %.
And here it comes: These 12 % are already our surface coverage. This means that on the total sheet of 1,000 x 700 mm we have a surface coverage for our pigment coating of 12 % - including coating bars and plate labelling.
You don't believe us?
Well, just try it out for yourself. Create a few test files, format 1,000 x 700 mm. Test half coloured with black and half coloured with white and then run through our process with these files and you will get a grey value of 50 %. Only a quarter black, rest white? Grey value 25 %. Believe us, this hack works highly accurately and you will always get an exact result for the area coverage of your colour separation, as long as you stick to our workflow. And of course this also works with halftones, i.e. greyscales. Only the individual dot gain of the selected printing process and print workflow would have to be multiplied later for a quantity calculation.
But what does this value do for us?
So now we know the area coverage of our pigment coating.
This means that 12 % of the surface of our 1,000 x 700 mm sheet is coated with our pigment varnish, the rest of the sheet (i.e. 88 %) remains uncoated.
Fine. What else?
The WEILBURGER Graphics coating quantity calculator
Well, we already programmed a coating quantity calculator for our customer WEILBURGER Graphics a few years ago, which is available both as a desktop version and as a web app as well as native apps for iOS and Android smartphones and tablets, is free of charge and with the help of which you can precisely determine the required amount of coating per job according to the selected printing parameters, anilox roller and print run.
You can find this coating quantity calculator here:
Native app for iOS
You can find the coating quantity calculator as a native and multilingual app (German, English, Spanish, Polish, Russian) for iPhones and iPads via this link:
Native App for Android
You can find the coating quantity calculator as a native and multilingual app (German, English, Spanish, Polish, Russian) for Android phones and tablets via this link:
Let's now play through the application with the iOS app using the pigment coating form:
First, we enter the sheet format and the planned print run incl. makeready sheets.
Then we select the correct anilox roller - in this project, a 16 cm3/m3 ART roller was used for the application of the pigment coating - and in the next field we also enter the area coverage of 12 % previously determined via our hack.
And our coating quantity calculator spits out both the wet application quantity (6 g/m2 ) and the 5.04 kg of coating required for this production.
Wait a minute...
...anyone who has ever stood at a press will surely wonder whether this is not far too little for a medium-format print job of over 10,000 sheets with a 16-unit ART anilox roller. Nothing arrives in the coating unit if you add circulation and filling. That can't be enough!
True! But this has already been considered in the coating quantity calculator and the additional quantities required for different press formats are also indicated.
This means: that in order to produce this print job reliably, we added the calculated coating quantity of 5 kg plus the suggested coating quantity for filling and circulation of 10 kg, and for safety's sake added another 5 kg for any additional makeready sheets that might be needed, unexpected press stops, etc. In the end, we managed well with the 20 kg of carrier coating.
And how much pigment is needed now?
Well, that's easy too, once you know the amount of coating you need and order the carrier coating and pigment separately. To achieve the strongest possible Iriodine effect, we planned to work with the maximum pigment concentration of 15 - 20 % that can still be processed in offset via the coating unit. So with 20 kg of carrier coating, we needed 4 kg of effect pigment (20 % of 20 kg).
As announced, here are the calculations for the other two lacquers:
SENOSOFT® WB MATT COATING FP NDC 350210
Area coverage: 42 %
Anilox roller: 13 cm3/m3 Hashur
Required lacquer quantity overlay o. circulation: 12.64 kg
SENOLITH® UV GLOSS LACQUER INLINE FP NDC 360424
Area coverage: 10 %
Anilox roller: 18 cm3/m3 ART
Required lacquer quantity overlay o. circulation: 4.73 kg
And the printing inks?
For printing inks - without going into too much detail - a rule of thumb has proven to be useful: Assuming a wet ink application of approx. 1.5 g/m2 , approx. 1 kg of ink is needed for 1,000 sheets in the 1,000 x 700 mm format.
Here too, depending on the job, between 150 and 500 g are added for filling, washing, make ready, etc.
This means that at 100% area coverage for this 3B job we would need for 10,000 sheets round about 10kg per colour.
If we now apply this to the area coverages of the four separations determined via our hack, the following values result:
Area coverage: 2 %
Required quantity of ink support incl. safety: 0.7 kg
Area coverage: 2 %
Required quantity of ink support incl. safety: 0.7 kg
Pantone Black 7 C
Area coverage: 30 %
Required quantity of ink support incl. safety: 3.5 kg
Pantone 376 C
Area coverage: 7 %
Required quantity of ink support incl. safety: 1.2 kg
Tip: In the WEILBURGER Graphics coating calculator you will find the SENOLITH®-TWIN-HYBRID-FINISHING tab further down. This area is normally intended for determining the quantity of printing varnishes and thus calculates with an average wet application quantity of 1.5 g/m2. Since you have already entered the job parameters print format and print run in the computer, you only need to open this tab and enter the already determined area coverage of the respective ink here and you will then immediately receive the quantity required for the print job for this ink (without the safety quantity).
Conclusion: The workflow presented in our first tutorial to create high-quality colour separations of all colour channels from print PDF files with Adobe on-board tools can also be used via this hack to determine the job-specific area coverage per colour channel.
If you additionally use calculation tools such as the WEILBURGER Graphics coating quantity calculator, this can even be used to determine the needed quantities of inks, coatings and - e.g. for cold transfer finishing - adhesive printing inks required for a specific job to calculate quotations, plan production or optimise costs.
If you liked this tutorial, please give us a Like or leave a comment. As mentioned at the beginning, we are planning to publish tutorials on all topics of our daily work in the printing, packaging and media industry - but also on software, app and web development - on a regular basis via this new newsletter and are of course looking forward to every feedback, recommendation, share and constructive criticism.
Social networks thrive on dialogue and exchange, and we look forward to an exchange with you!
PS: The packaging project reviewed here, together with the associated tutorials and further information, can be found on the PrintCity website.
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