Archive for the ‘Density’ Category

Color Measurement the Right Way

Quality printing depends on precise color measurement, which makes it all the more relevant to ask why different measuring devices often produce different results. What should you rely on in this case?

Modern color measuring devices are generally based on spectrophotometers, even if they only show densities. This is because of the higher measuring accuracy of spectrophotometry, together with a greater range of available measurement values. The measuring conditions set on the devices therefore not only need to be selected correctly but must also be identical for all devices. The correct setting often depends on the country. Regional associations such as the bvdm in Germany and CGATS in the United States formerly laid down these conditions. Today they are to be found in the relevant ISO standards. Settings can be made for the following values:

Illuminant: This defines the color temperature of the lighting source. For printing, the standard is currently D50, which corresponds to 5,000 Kelvin.

Observer angle: The standard observer angle in printing is currently defined as 2°. This corresponds to the printer’s observation angle in the matching stage.

Density filter: This determines the spectral range that is to be used to calculate the density values for CMYK. Standards “Status E” (= DIN 16536) and “Status I” (= DIN 16536 NB; narrowband) are usual in Europe. “Status T” is used for measuring in the United States.

Polarization filter: Polarization filters eliminate the gloss of wet ink. The wet values therefore correspond almost entirely to the dry density and tonal values.

White reference: The “absolute white” setting is preferred for density measurement in North America. In all other countries, the white reference is “relative.” Paper white is therefore always taken as the zero point here. To match a spectrophotometer to an old densitometer, it is necessary to know the densitometer’s settings precisely and apply exactly the same parameters to the spectrophotometer. Despite identical settings, minor deviations may occur even within a group of spectrophotometers. These are generally due to the quality and design of the sensor and its calibration. Theoretically, every spectrophotometer should be calibrated to absolute white and black. However, in practice neither one exists, which means it is best to use reference values from an independent institution such as the German Federal Institute for Materials Research (BAM) in Berlin. Manufacturers can have a device calibrated here and use this “master device” to calibrate all other devices. The better the measuring device, the narrower the tolerances that the manufacturer defines for the ΔE and density values. And the smaller the tolerances, the greater the measuring accuracy.

To ensure the measuring accuracy remains constant for as long as possible, users are well advised to have devices serviced and calibrated regularly. Heidelberg is the only press manufacturer to offer a software option – the Prinect Net Profiler – that enables printers to personally calibrate almost all new-generation Prinect color measuring equipment, even including colorimetric calibration. This ensures devices are always close to the factory settings and therefore deliver highly reliable results.

It is also advisable to designate a selected spectrophotometer as the “master” in the print shop itself. This ensures maximum measuring accuracy and, ultimately, print quality across several work stations.

Typical distribution of measuring device deviations – the blue dot in the center is the ideal value for the reference device. The grey circle shows the permitted tolerance. The red dots represent the deviation for different measuring devices.


ISO 12647-2 Presswork Procedure

Quite often we get the question of how to achieve ISO-12647-2 standards in press (not for certification purpose ofcourse).  So decided to write down the steps need to be followed.

1. We have to make a test form with linear plates (test form high-res file is with Mr.Saravanan of Heidelberg). A linear plate means, input and output value has to be same. If we give a value of 50%, the plate should have 50% only (+ or – 1% tolerance)

2. Print this linear plate in the press with the pre-requisites below with varied densities across the sheet

3. After the print is allowed to dry 3 hours, measure the sheet and find the optimum density for the press using Delta E and Contrast method.

4. Then print another test chart with the calculated optimal density (linear plate) and calculate the dot gain deviation.

5. The dot gain deviation has to be calculated and compensated in the RIP as per ISO 12647-2 standards

6. The same test chart to be printed with revised dot gain curve

7. The iteration should continue until the best results are achieved as per ISO 12647-2 standards

8. The Pre-press need to be set as per the “ISOcoated V2.icc” and proof need to be FOGRA 39 standard in V3 media wedge.

But to do the above exercise, we need to have the below

• Should have a densitometer and also a plate (Calibrated one. Prefered instruments are Ihara R730, Techkon Spectrodens for press and Ihara Accudot or Techkon spectroplate for plate dot measurement)

• you need to print minimum of 3000 sheets of your full paper size of 115/135 gsm art glossy paper with Fresh CMYK ink in the inking unit. When the target is the ISO 12647-2 standard, the used ink series should be ISO conform. Values given below for reference. We can check Ink manufacturer for the confirmation.

• The printing press has to be in a well maintained condition

• Blankets need to be in a clean and proper condition

• New blankets should be washed with water and cleaning solvent

• Verify the blanket tension with a torque key (for tension values check the machine manual)

• The Packing has to be done as per the standards

• The Pressure between blanket/plate have to be in a range of “kiss print”

• The Pressure between blanket/substrate have to be in a range of “kiss print”

• The Ink deck have to be washed clean

• All rollers have to be well adjusted

• Ink- /dampener rolls have to be well adjusted especially to the plate

• The ink distributor roller have to be checked

• Verify the machine manual for adjusting the rollers according to the machine manufacturer

• The pH-value of the fountain solution should be at a level between 4.7 – 5.3

• The percentage of alcohol in the dampening solution should be at a level between 5 – 10%

If you have any doubts are clarifications, please feel free to come back to us


Pre-flighting is a term used in the printing industry to describe the process of confirming that the digital files required for the printing process are all present, valid, correctly formatted, and of the desired type. The term originates from the pre-flight checklists used by pilots. The term was first used in a presentation at the Color Connections conference in 1990 by consultant Chuck Weger.

Source: everydaycolormanagement.jap

VIGC study on spectrophotometers reveals: instrument accuracy can be a nightmare

Quality assessment in the graphic arts industry depends mostly on the use of spectrophotometers. Printers use them to check their production processes, customers use them to evaluate the print job for acceptance. Quality demands are getting more strict every year, the spectrophotometer decides whether a job is accepted, or not. But when VIGC, the Flemish Innovation Center for Graphic Communications, did a study on the accuracy of those devices, they found deviations up to a delta E of nearly 4… Which means trouble in the printing industry.

“Color quality is the biggest challenge in the printing industry.”, says Eddy Hagen, managing director and trend watcher of VIGC. “Graphic arts companies will try everything to get the colors as desired by the customer. Those customers will use it as the most important criterion to accept, or reject, a print job. Which makes the devices to measure that color quality quite essential. So you would expect that the quality of those devices is top class. But it isn’t.”

After having experienced some issues with different devices, VIGC started their first tests to compare multiple devices in the summer of 2007. “We saw some deviations between the different spectrophotometers that we use ourselves.”, explains Fons Put, senior consultant with VIGC. “So we set up a procedure to check and compare different devices. As the reference we used the GretagMacBeth NetProfiler test chart. This is a test chart which comes with a certificate stating the L*a*b*-values of the different patches, measured with three spectrophotometers under ideal conditions (updatet 14/09/2008). The certificate is valid for 12 months only, so it needs to be renewed every year. And then we measured the 13 patches on the test chart with different spectrophotometers. For two patches we also measured the repeatability of the devices, meaning 10 measurements in a row.”

Deviations up to delta E 3,77

Over the past year, VIGC has tested over 20 different devices, most of them are used by printing companies that VIGC is working with. This is in contrast with similar, smaller studies that have been done in the past. Other studies used devices that they got directly from the vendors. VIGC tested devices that are out in the field, that are used on a daily basis by companies in the industry. This gives them a very interesting overview of the capabilities of spectrophotometers in daily life. And those capabilities are not what people think… When a customer demands a maximum delta E of 2, which is often the case for quality print jobs in Belgium, he wants a device that measures the color as accurate as possible. However, the VIGC study revealed deviations up to delta E = 3,77 for specific colors. On average the deviation per instrument of all 13 patches is 1,56.

Different types, different brands

In the study VIGC encountered multiple devices of the same type or the same brand. Is there a relation between the type, the brand and the accuracy? “That’s an interesting question.”, says Put. “There was one general rule: the newer types of devices perform better. With devices that were a few years old, sometimes we got good results with the first one and bad results with the second one. Our own main spectrophotometer, which is calibrated regularly on that NetProfiler chart, was the best of them all. Another device, the same brand, the same type, more or less the same age, performed really bad.” When the measurements of all 13 patches were averaged per device VIGC found deviations from the exact value ranging between delta E 0,45 for the best device and 2,74 for the worst one. Which means that several devices showed – on average – higher deviations than the margins that customers expect from their printers for high quality print jobs. The highest deviation for individual patches was a delta E of 3,77. “Also interesting – or disturbing if you like – was that one brand had quite strong deviations in the red and orange. We found this on multiple devices of that specific brand.”

Even within a certain type of device, VIGC found very big differences. This graph shows the deviations from the absolute value for 7 devices of the same brand, the same type.

What causes the deviations?

With the older devices one major reason can be maintenance… “We know that some devices performed bad because the optics or the calibration tile were dirty.”, explains Put. Spectrophotometers need regular calibration and also periodic cleaning. Another reason can be the light source used. Put continues: “No light source has a perfect ‘spectral power distribution’. And if you don’t have much power in certain wavelengths, not that much color can be reflected in that region, which limits the accuracy of detecting small variations in that color region. An LED light source has a completely different spectral power distribution from a gas filled tungsten bulb. And both are used in spectrophotometers.”

This graph shows the difference in composition of the light source used in two different spectrophotometers.

Why not delta E 2000?

The big differences that were found can cause trouble: customers demand a delta E of 2, but their measurement device might be of a delta E of 3… A simple – and valid – solution for the industry would be to accept delta E 2000 as the formula to calculate color differences. “When people talk about delta E, they usually refer to delta E*ab, also known as delta E 1976. This is also the formula that is mentioned in the relevant ISO standards. But this formula is very inaccurate when it comes to small color differences.”, says Hagen. “I can show you a pair of colors with color difference of delta E 5 which is barely noticeable… Take a 100% and a 95% process yellow from ISOcoated. The deviation is just noticeable, but if you calculate it with delta E*ab, you get a figure of 5. Delta E* ab doesn’t really conform to the human perception of color differences. The newer delta E 2000 does. Take the same yellow color pair and you will get a delta E of approximately 1. Which conforms to the initial idea of delta E: a delta E of 1 is the smallest noticeable color difference.”

Download this testfile: how big is the color difference between the left and right? When measured this will give a very high delta E*ab, although the difference is barely visible.

When the test results of VIGC are recalculated with the newer delta E 2000, the figures become much more realistic. The overall average of all devices on the 13 patches is a rather bad 1,56 when delta E*ab is used, but a very good 0,39 when calculated with the more recent delta E 2000.

Hagen continues: “The bizarre thing however is that some experts don’t want to use delta E 2000 because it is not that good when it comes to rather large color deviations. In those cases the old delta E*ab performs better. But who is interested in the accuracy of large color deviations? I want accuracy in small color deviations. That is where the battlefield is, where print jobs get rejected. Not because the colors look very different, but because the delta E formula states that they are different… The printing industry would benefit a lot if the delta E 2000 formula would be the official formula for calculating color differences. But all relevant ISO standards only seem to know delta E*ab… Even the draft for the upcoming update (updatet 14/09/2008) of ISO 13655 on color measurement only talks about delta E*ab. Which is not in favor of the printing industry, nor their customers.”

Conclusions and recommendations

What should we learn from this study? First of all that the measurements from a spectrophotometer – at least the ones used in the graphic arts industry – is not absolute. There can be variations between different devices. Also the devices need to be calibrated on a regular basis and need to be maintained in a proper state. Periodical cleaning by the vendor may seem expensive, but what is the cost of a – perfect – print job that gets rejected due to the fact that the spectrophotometer was lacking maintenance and therefore showing a wrong figure?

Also the industry and the standard organizations need to consider using delta E 2000 as the standard to calculate color differences when judging print quality. For small color differences delta E 2000 conforms much better to human vision than delta E*ab. Rejecting jobs because of color differences should be about seeing differences, not just about measuring a certain number.

VIGC’s response to some comments
Our article caused some stir in the industry. And that was our intention: we wanted to create awareness on the issues, we didn’t want to ‘condemn’ the vendors of spectrophotometers (otherwise we would have mentioned names…). Spectrophotometers are specialised tools, they need to be handled with care and with the appropriate knowledge. With care, that means: maintain them well! E.g. regular maintenance by the vendor is a cost, but it really is necessary. With the appropriate knowledge, that means: know how to use them in the right way, know how to interpret measurements and set goals that can be measured undisputedly.

In the article, a few points have been updated, based on the input we got (btw: thanks to all who delivered input!). Below is some more information on other comments.

VIGC only did one measurement, they should have taken three measurements and averaged the results
Yes, we only did one measurement and we should have done three, to have a real scientific approach. But, how many printers or print buyers do it that way? We have chosen to test spectrophotometers in the same conditions as they are used in the industry. And most printers and print buyers just take one measurement… Which can be very dangerous! Several years ago, we did a test with a ‘cold’ spectrophotometer (first use on Monday morning in winter time): it took over 10 measurements before the results were more or less consistent!

The measured devices were within ISO-specifications for spectrophotometers.
Yes, indeed. And this brings us to the goal of our article: create awareness. Many customers are demanding tolerances that are tighter than the ISO-specifications for printing (ISO 12647). With a tolerance that is often lower than the inter instrument deviation that is allowed according to ISO specifications for spectrophotometers, you will get trouble. What if the print buyer specifies a target color in CIELAB and the measured color is outside the – small – tolerance, only due to the deviation of the device used? That would mean that a job that got rejected – with either a reprint or a price reduction – for the wrong reasons! That’s why we wanted to create awareness.

A company always uses the same device, so inter instrument deviations are not that important.
Not always the case! We can’t put a percentage on it, but certainly in the case where the print buyer also has a quality department, they will check – and approve or reject – the print job with another device, maybe even with another brand of spectrophotometer. So in that scenario, where both printer and print buyer check the colors of a job, according to a specified color (e.g. a brand color), inter instrument deviations can play a significant role. And we’ve seen this in real life: printer measures the job within specs, print buyer measures it and it is outside the specs… Job got rejected.

To conclude an anecdote to illustrate why we wanted to create awareness…
A few years ago we got contacted by a printer of corrugated boxes. He was in the running for a really large order, but the customer had set quality targets and he didn’t know what to do with them… The maximum delta E that the customer had specified, was – if my memory serves me well – a delta E of 3 (since they didn’t specify which delta E, we assumed it was delta E*ab). Now consider that this was on brown corrugated boxes… The substrate itself has color differences that exceed delta E of 10! It is covered with dark spots… The customer delivered a printed ink sample. However, this was printed with a hand roller, on a nice glossy extremely white paper… and that was the color reference for printing on brown corrugated. The ink sample itself was full of lighter and darker areas, so which color was the reference??? But in the end, a certain amount of boxes should be sent to the quality department of the print buyer. And they would measure it, with their device – which was a completely different type of spectrophotometer than we are using in the printing industry – and approve or reject the print job… This is just a way to be sure to find a reason to reject jobs and demand a discount… This is not about getting the colors right anymore.

Color is something really complex and you need the right skills, the right equipment to get the colors right, to measure them in the right way.


Brilliant colors true to the original on a premium surface – that ̓s what distinguishes a high-quality print product. Many elements in prepress and printing impact on a product ̓s color fidelity. The various input and output units in a print shop ̓s production process, consumables and other factors can cause deviations in color. A consistently employed color management system eliminates this problem.

In this series of blog tips we ̓ll show you the most common sources of error and give you tips on color management. We ̓re pleased to have caught your interest.

screen rulings

Different screen rulings produce different levels of dot gain during printing and thus different representations of an image.

Different screen rulings have to be calibrated differently in order to make the images match. CtP technology allows you to easily adjust the plate characteristics so that the same tonal values can be reproduced in printing, independent of the

screen rulings. This makes it possible to achieve a unified print image.

To be continued…

With reference Heidelberg Profitip series…

Brilliant colors true to the original on a premium surface – that ̓s what distinguishes a high-quality print product. Many elements in prepress and printing impact on a product ̓s color fidelity. The various input and output units in a print shop ̓s production process, consumables and other factors can cause deviations in color. A consistently employed color management system eliminates this problem.

In this series of blog tips we ̓ll show you the most common sources of error and give you tips on color management. We ̓re pleased to have caught your interest.

Step 1: Choose Consumables

Consumables have a very large influence on the print result. Deciding on set materials creates a basis and defines the boundaries. Changing consumables produces new results, which may necessitate recalibration. Thorough planning is, therefore, required. Examples of consumables include:

 Printing stocks

 Inks

 Blankets and underlays

 Dampening solution (additional amount + IPA)

 Printing plates and development chemicals

 Proofing paper and ink

1. printing plates

Different levels of dot gain can be generated depending on the water flow and ink absorption. This can cause the color dimensions to lie within or outside the range of tolerance depending on the type of printing plate, even when the same ink is used.

a. Printing plate type A: Color dimensions within the range of tolerance

b. Printing plate type B: Color dimensions outside the range of tolerance

2. Inks

Different inks can generate different levels of dot gain. This can cause color dimensions to lie within or outside the range of tolerance depending on the ink that is used.

c. Ink type A: Color dimensions within the range of tolerance

d. Ink type B: Color dimensions outside the range of tolerance

To be continued…

With reference Heidelberg Profitip series…

Speaking Color

You’re late for a meeting with the designer who is redoing your offices. On the way into the conference room, you pass a colleague who says the new colors are “gross.” You enter the room and get a full presentation on a grey and mauve color scheme that looks really nice to you. Later, you ask your colleague about her comment and discover that “gross” actually meant “out of fashion.”

If we could get inside each other’s heads, communication about color would be more accurate. Since we can’t, we must fall back on language to describe what we perceive. There are some, like Mary Buckley, an artist and educator, who believe this is a good thing. She says that “detecting and naming attributes is basic to developing an understanding of light and color.”

Indeterminate, or nonmeasurable, attributes, such as shocking pink and clear-sky blue, are more than just adjectives. They are terms we use to explain the effect a color has on us. They are the words we use to describe our state of mind as we experience colors. Buckley is among a growing number of colorists and designers who believe that naming the intent of a space through the use of indeterminate attributes must occur before any discussion of specific colors. Users should first respond to the question “What should the space feel like?”

The subjective responses to this question will direct designers in their color choices. Sometimes these indeterminate attributes verge on a synesthetic response: They use the language of one sense to describe the perception of another, as in loud pink and tart green. But perhaps the most interesting attributes we commonly use are warm (reds, oranges, and yellows) and cool (greens, blues, and purples). These divisions are deeply embedded in our thinking, as evidenced by the red faucet for hot water and the blue for cold found in most washrooms, even though the actual temperature of red light is cooler than that of blue light.

With the advent of the Industrial Revolution, however, the focus shifted away from a reliance on language to communicate color. In order for manufacturers with plants scattered around the country to maintain color consistency in their products, they began searching for a new technology that would provide accurate color definition. During the last half of the nineteenth century, several people developed more precise ways to describe specific colors. They based their work on three basic, universal, measurable characteristics of color: 1) which spectral category it belongs to; 2) how light or dark a color is; and 3) how brilliant or dull it is.

Color terms for these characteristics vary. Some use the distinctions warm/cool, light/dark, and brilliant/dull. Others speak of hue, value, and chroma. Hue is the basic name of a color, such as red, yellow, green, or blue. Value indicates how light or dark a color is. Chroma is the amount of hue in a color. For example, vermilion has a great deal of red but pink has very little. Munsell’s System describes color in three dimensions. The American art educator Albert Munsell (1858-1918) developed the widely used

Munsell Color System, which arranges all colors on the basis of their appearance.

He was the first to call the three main characteristics of color “hue,” “value,” and “chroma,” likening them to a musical note’s pitch, tone, and intensity. Others, such as the German chemist Wilhelm Ostwald (1853-1932), developed color systems based on different scientific principles. But all color systems share one common feature—they all map the three characteristics of color in three dimensions on XYZ axes. According to Sloane, “Dimensions beyond these three exist, although we do not know how to incorporate a fourth or further spatial dimension into the model graphically. Colors, for example, can vary in shininess of surface. The Munsell System acknowledges this parameter but suggests no way to incorporate it into the three-dimensional color solid.”

(More to continue.. Enjoy reading of