Sunday, April 25, 2010

Printer in Kentucky is closest to Quality

It's true, Printer in Kentucky is closest to Quality.

The community of Printer Kentucky.

The community of Quality Kentucky.

According to Google Maps, Printer and Quality are only 5 hours and 19 minutes apart.
Compare that to the distance from Printer in Kentucky to the lack of substance in Quality California:
Quality California.

Quality in California is a whopping 37 hours away from Printer.

Now some people argue that Luck is involved with Quality:
Luck Wisconsin.

Well according to Google maps, Luck and Quality are 14 hours and 30 minutes apart:
That's quite a separation so it's doubtful that Luck is involved with Quality. But there's even a greater separation between Luck and Printer - a 16 to 17 hour separation in fact. So Luck and Printer probably don't go together at all.
I know that this relationship between Printer, Quality, and Luck may be strange. However, the facts can be verified by anyone by going to http://maps.google.com/ or http://www.bing.com:80/maps/

Wednesday, April 21, 2010

Tolerancing color in presswork - CIE L*a*b* and DeltaE

This method attempts to bring an objective, system independent, instrument-based method to color tolerancing. Because this method uses instruments to define colors, the range of tolerance and deviation from the target it is considered to be objective and unambiguous. It is much more sophisticated than the more subjective methods so far described in my other posts. As a result, a bit of background knowledge about color science is needed in order to understand how this system works and to understand its value and potential pitfalls.

A scientific approach to describing color
From a color science point of view, any color can be described by three basic attributes:

1) Lightness. This is the attribute of a color by virtue of which it is discernible as bright, dark, or somewhere between those extremes.
2) Chroma.This is the attribute of a color by virtue of which it is discernible as purity or intensity of color relative to a neutral color like grey. Also referred to as "saturation."
3) Hue. This is the attribute of a color by virtue of which it is discernible as red, green, etc., and which is dependent on its dominant wavelength, and independent of intensity or lightness.
So, from a scientific point of view, describing a color requires three values/numbers. One for Hue, one for Lightness, and one for Chroma.

Describing a specific color this way can be visualized as finding the location of a specific room in a building.One goes up a central elevator representing the range from neutral dark to light. Then one gets out of the elevator at a specific floor/specific lightness level and travels outward from neutral grey to an increasing amount of chroma/saturation as they move toward the outside edge of the building. Once they reach the desired amount of chroma/saturation one moves to the left or right to find the specific room/hue. So, directions to the specific room/color can be expressed as a recipe: Up X levels (lightness/floor level), Move X Distance (Chroma/Down hallway), Move X degrees (Hue/Along perimeter) = Room/Color.

This three coordinate method of describing a color can be visualized in cut-away form as in this graphic:In reality this 3D color space map is more complicated (you can see a movie of a real 3D color space HERE). However it should be good enough to explain this complex subject.

This three coordinate system (LCh) can then be used to map the location of a specific color.
Unfortunately, LCh has not been widely adopted to describe a color's location within a color space. Instead, the less intuitive L*a*b* notation is most commonly used. L*a*b*, more properly written CIE L*a*b* uses the same 3D model but identifies the color according to it's "L" lightness, "a*" axis value (+a* = more red, -a* = more green compared to neutral grey) and "b*" axis value (+b* = more yellow. -b* = more blue compared to neutral grey).

Defining a color location using CIE L*a*b* coordinates
Using the three coordinate CIE L*a*b* system allows us to numerically identify any color within a color space. In this example, I'll use a print color space and identify the desired color within that color space:
Tolerancing a color using CIE L*a*b*
Color tolerancing using CIE L*a*b* involves comparing the measurements, taken with a spectrophotometer, of a color sample (the output) to the data of a known color (the specification or input value). Then the "closeness" of the sample to the specification is determined. If the sample's measured data is not close enough to the requested color values, it is deemed to be unacceptable and adjustments to the process may be required.

The amount of "closeness" between two colors can be caluculated using a variety of methods. These methods calculate the distance between the two sets of measurement coordinates (e.g. CIE L*a*b* values) within the three dimensional color space. The size of the distance is defined by the size of the tolerance and is expressed as a "DeltaE" value (Delta Error).

To calculate the "closeness" of the specified color and the sampled color, the specified color is pinpointed by its position in CIEL*a*b* color space. Then a theoretical "tolerance sphere" is plotted around the color.The sphere, with the specified color at its center, represents the acceptable amount of difference between the specified color and other measured samples (the color output). The actual size of the tolerance sphere is determined by the customer's specification's for acceptable color difference. The tolerance value is expressed in delta (∆) units such as ∆E usually written as DeltaE (delta error). Measured data that falls within the tolerance sphere represents acceptable color.Measured data that falls outside the tolerance sphere represents unacceptable color.

Typical customer tolerances in the graphic arts industry usually range between 2 and 6 ∆E. This means, for example, that samples outside the tolerance sphere lie more than 6 ∆ units away from the specified color. Tolerances less than 2 ∆ units are typically unachievable given normal process variation. Differences between two colors that are up to 4 ∆ units away from each other are usually not visible to most viewers.

Issues, concerns, and caveats when using CIE L*a*b* DeltaE tolerancing
While this method can bring an objective and potentially unambiguous method to color tolerancing there are several issues to be aware of that can cause misunderstanding and error.

1) CIE L*a*b* DeltaE tolerancing is instrument dependent, however, different instruments can deliver different values from the same color sample.
Some of the reasons include: poor maintenance of instrumentation, infrequent recertification by the factory, lack of periodic verification, spectral bandwith differences, lack of geometric tolerances, variations in fluorescence in the substrate and instrument illuminant, instrument and environment induced noise, dark current drift, variations in ambient conditions, thermochromism (ink changes color due to a change in temperature), hygrochromism (humidity changes the way ink interacts with paper and hence its color).

2) CIE L*a*b* DeltaE values are dependent on the formula used - and there is no universally agreed standard for the formula that should be used.
Some formulas are: DeltaE 76 (sometimes referred simply as DeltaE), DeltaE 94, DeltaE 2000, and DeltaE CMC. In general, DeltaE 76 values are highest, DeltaE CMC values the lowest especially for saturated colors, DeltaE 94 and 2000 are lower than DeltaE 76 but higher than DeltaE CMC.

For example, these two color patches are made up with the indicated CIE L*a*b* values:The DeltaE difference between these two colors as reported by the different color difference formulas:
CIE 76: 7.10 (a large difference - unacceptable)
CIE 94: 1.51 (well within typically acceptable variation)
CIE 2000: 1.57 (well within typically acceptable variation)
CMC: 2.26 (within typically acceptable variation)

So, depending on the formula used to calculate the difference in color a measured sample may, or may not, be within acceptable tolerance.

3) It is harder to see the differences when colors are very saturated. It is easy to see a difference when colors are near neutral.
Formulas like CIE 94 attempt to compensate for this difference in visual color acuity, however, it is not the predominantly used formula. That honor goes to CIE 76. It's therefore important when discussing color variation to specify which formula is being used to calculate DeltaE values so that the numbers can be better interpreted.

4) The color performance of a system or press sheet is sometimes reduced to a single DeltaE value as a statement of being within tolerance. This can be very misleading since the single DeltaE value is an average of all sampled colors and will likely not reflect the performance of specific critical colors.
Statements such as "This press sheet is within 2 DeltaE of the proof" are virtually meaningless.

5) There are no CIE L*a*b* controls on a press.
If a color on a press sheet is out of DeltaE tolerance - the press operator effectively has to guess at what should be done to correct the problem using tools not designed for this function like solid ink density, water, impression pressure, etc. to effect a change in color.

Sunday, April 18, 2010

Presenting Season Two....

Each week, famed chef and Michelin Star winner Chef Gordon Ramsay steps out of his own five-star establishments and into some of the country's most interesting restaurants to help them turn their businesses around, or close their doors forever, in the hit TV show Ramsay's Kitchen Nightmares.

Whoa, that's one of the things that I did during my tenure at Creo/Kodak. Not with restaurants though, but with printshops. So step aside Chef Gordon Ramsay - this is where the blanket really hits the plate as revealed in a few more of the conversations I had with printers during those years. (Season One is HERE)

Chef Gordo: "I can't believe it! The file was RAW!"

Chef Gordo to printshop owner: So how do you manage your quality? Who sets the standard?
Printshop owner: That's easy, Frank - the lead press operator on the CD 102.
Chef Gordo: One of your press operators is responsible for your whole shop's quality standard?
Printshop owner: Yeah, sure, Frank's got "the eye" for quality.
Chef Gordo: Bloody hell!

Chef Gordo to printshop owner: So why would a print buyer favor your print shop rather than the one down the street?
Printshop owner: Because we're a quality printer.
Chef Gordo: But that's what your competition says about their shop.
Printshop owner: Well, yes maybe, but we're the quality printer.
Chef Gordo: Bloody hell!

Chef Gordo: "You must be joking!"

Chef Gordo to prepress and pressroom: Your presswork and proofing don't seem to be in alignment. Who set you up?
Prepress and pressroom: I think our vendor did when we first got their equipment.
Chef Gordo to prepress and pressroom: So how was it set up? Who's in charge of maintaining it?
Prepress and pressroom: Let's see. We're not sure. It was working before. But we've changed inks, blankets, and fount solution since then. Is that important?
Chef Gordo: Bloody hell!

Chef Gordo: What's that smell?
Printshop owner: Oh, ah, that might be Mongo.
Chef Gordo: Mongo?
Printshop owner: Yeah, he does all our deliveries.
Chef Gordo: I see, so Mongo delivers your presswork to your customers smelling like an abattoir?
Printshop owner: Well, he's cheap. I mean he's cost effective.
Chef Gordo: Bloody hell!

Chef Gordo - Bloody hell! See you next time!

Friday, April 16, 2010

How to print from Apple's iPad

"Nature finds a way."Print prevails with this innovative technical breakthrough achieved by the folks HERE.

Sunday, April 11, 2010

A different side of Steve Jobs

Steve Jobs is much in the news these days with the iPad and iAd. His "reality distortion field" when introducing new products is the envy of many marketeers. This though is a different side of the man. From www.ted.com, Steve Jobs, CEO and co-founder of Apple and Pixar, urges us in this 14 minute inspirational talk at his Stanford University commencement speech in 2005, to pursue our dreams and see the opportunities in life's setbacks - including death itself.
video
Click play arrow (and maybe wiggle the play head), to view the video.

Friday, April 9, 2010

Finding a "Quality" printshop

Most printers would consider themselves to be "quality" printers. A very few actually put it in their business name. A quick search on Google and a bit of help from street view quickly revealed these boldly self described quality printing establishments. Is there a quality printer in your location?

Wednesday, April 7, 2010

How to calculate halftone dot sizes in microns

When working with screen rulings, particularly those above 200 LPI or FM screening, you may need to know the size of dots in microns. This is to make sure that the plates, plate imaging system, press, and ink pigments are all capable of delivering the minimum printing dots through the process. For example, if the dot size is 10 microns but the ink pigment size is 25 microns there may not be enough dot surface area for the pigment to stick to and hence that tone will be dropped out on press. Or, if the screen calls for a 10 micron dot but the plate can only hold a 20 micron dot then, again, that tone will be lost or have to be compensated for by employing hybrid screening techniques.

Dot diameter in microns can be calculated using the following formula.
Where:
D = Dot area in percent (e.g. 1% dot equals .01)
F = Screen frequency in lines per millimeter (LPM)

To convert the screen frequency from lines per inch use the following formula (2,540 dpi device on left and 2,400 dpi device on right):
While this formula is not absolutely exact, it gives a close enough approximation for most practical purposes.

A few things to keep in mind about halftone dot size. The formula applies to the size of dot that is generated by the halftone screening algorithms in the RIP that will be sent to the imaging device. It does not calculate the size of the dot that appears in the final presswork which may have been affected by dot gain or loss. Also, a RIP will only image full individual pixels to form a halftone dot. So, in the case of a 2,540 dpi device, each pixel is 10 microns in size (10.6 microns for a 2,400 dpi device). Therefore, if, for example, the formula says that the final diameter of the dot is 15 microns what will happen is that the RIP will alternate between 1 pixel dots (10 micron) and 2 pixel dots (20 micron) which results in an effective 15 micron dot average for that tone value. You can see that happening by watching the dot formation in the lighter tones at the start of the video located HERE.

Below is a quick reference comparison chart showing the dot diameters for tone values of 1% and 2% for various screen rulings from 10 LPI to 400 LPI on a 2,540 dpi platesetter.Highlighted areas are where the required dot is smaller than a single pixel at the device's resolution and therefore will not be imaged.

Sunday, April 4, 2010

Write it down. Document it. Now.

Production mistakes happen. It's part of the business. Hopefully they get corrected and the print shop moves on. What's frustrating is when the same mistake happens again. One good way to avoid making the same mistake twice is to document it in a journal.
Two of my old "print experience journals" filled with technical production notes, test results, samples, and odds and sods of print-related information.

A "print experience" journal can be used to document mistakes and how they were corrected, prepress/press tests and results, samples of interesting print effects, and technical bits and pieces of information. Some print shops create a database, hosted on a server, of this type of information that CSRs, sales people, estimators, and production people can both access and add to.

Documenting production experience in an accessible form, like a journal or database, helps the shop learn from its past and reduce the chance of making the same mistake twice. They can preserve the knowledge inside the company even when key employees leave the business.