Saturday, February 20, 2010

Presenting...

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 some of the conversations I had during those years. (Season 2 can be found HERE.)

Chef Gordo to prepress: Do you use any kind of plate curves?
Prepress: Absolutely. We run all our plates dead linear. 50% in the file is exactly 50% on the plate.
Chef Gordo to prepress: But you run different screen frequencies and sometimes FM screens don't you?
Prepress: Yes. But we're quite proud that no matter what screening we use, our plates are dead accurate linear.
Chef Gordo: Bloody hell!

Chef Gordo to prepress: What are those proofing booth lights?
Prepress: Ah, well, management orders those.
Chef Gordo: OK, so what are they?
Prepress: I think they're cool white fluorescents. They might be warm though.
Chef Gordo: Not D 5000s then?
Prepress: No, I think management figured these were just as good - but much cheaper.
Chef Gordo: Bloody hell!

Chef Gordo to press room: That's a German press with closed loop color control, yes?
Press operator: Yeah.
Chef Gordo to prepress: Your Spectro's are from where?
Prepress: The U.S. of course.
Chef Gordo to press operator and prepress: Do you realize that your instruments are set to completely different standards? It's like one department is speaking Euro and the other U.S.
Prepress to Pressroom: Sh*t! So when we ask for certain densities your instruments report different numbers?
Chef Gordo: Bloody hell!

Chef Gordo: "Oh my Gawd!"

Chef Gordo to prepress: What are the target densities that the pressroom runs to?
Prepress: Uh, well, K: 1.70, C: 1.40, M: 1.40, Y: 1.05 - I think.
Chef Gordo to press room: What are the target densities that you run to?
Press room: Let's see, you mean typical? I think they're about K: 1.60, C: 1.30, M: 1.20, Y: 0.90
Chef Gordo: Bloody hell!

Chef Gordo to press room: When was the last time you calibrated your instruments?
Press room: Well, I'm not sure.
Chef Gordo: Not sure? Where's your calibration target? Your records?
Press room: Well, I'm sure they're around here somewhere. Frank! Have you seen those funny looking color patches around somewhere?
Frank: Color patches? Gee, I don't remember. Color patches, eh? Hmmm.
Chef Gordo: Bloody hell!

Chef Gordo - Bloody hell! See you next time!

Thursday, February 18, 2010

Fashion in the pressroom

In well run printshops the owners will usually provide prepress and pressroom workers with clothing, in part to present a clean unified look to visitors and customers. However, there are some outfits that should never be seen near the press.

Here are two prime examples of pressroom-fashion faux pas:

From North America:
From Japan:
Apart from their difference in weight, what is their sartorial sin? In a word, color. The color of what is worn gets reflected into the press sheet color. It can be a difficult problem to be aware of since our eye/brains instantly auto-white balance - so white paper will still look white. Unfortunately, the red or blue outfits in the above examples will distort the hues of the color in the presswork and may lead to incorrect color adjustments.

However, the below fashionistas are more in keeping with the discipline of the press room:Grey shirts, grey pants, and optionally, grey hair. Grey balance on press and grey balance in the closet.

This rule also applies to print buyers/specifiers when conducting a press check. To evaluate color effectively wear the neutrals, black, white, grey.

Sunday, February 14, 2010

The principle of dot gain compensation plate curves

In a film workflow the industry standard was to create film output that was linear. This meant that a 25% tone request in the original Postscript file would create a 25% dot on the film, a 50% request would create a 50% dot, and so one for all requested tone values. However, in a CtP workflow controlling tonality in the print reproduction process, allows you achieve the presswork quality you want without adjusting the press. It also provides the flexibility to tailor the print characteristic to meet different customer expectations.

Dot gain, or tone value increase (TVI), is a normal part of the print reproduction process. Controlling tones using calibration means that you can manipulate the exact size of the dots on the printing plates so that tone saturation and gray balance are controlled on the press sheet.

Tonal calibration can account for:
• type of plate or film used
• type of paper stock used for printing
• type of dot shape used
• type of screening used—for example, FM/Stochastic or AM/XM conventional, and frequency (lines per inch (lpi))

(Note: Adjusting CtP laser exposure is not tonal calibration and will affect the run length and performance of the plate.)

You cannot use tonal calibration as a substitute for stable operating conditions. Operating conditions must be controlled as a separate process. In fact, without a stable operating environment, you cannot achieve accurate tonal calibration let alone reliable press output.

What Is Tonality?

Printers are used to being concerned with dot gain/TVI. Indeed dot gain values are often included in printing specifications. However, for the purposes of calibration - tonality or dot area, rather than dot gain, is the key metric. It does not matter what dot gain you have. What matters is whether you achieve the required final tone values or dot areas at each originally requested tone.
On the left is the desired "correct" tone reproduction and on the right is incorrect tone reproduction.

Tonality in printing is the progression of tints from blank paper to solid ink for each requested tone value in a printing job. It is measured with a densitometer, and reported as either dot gain/TVI or dot area:
Dot area and dot gain - two ways of charting the same data.

The target print characteristic tone curve

Building dot gain compensation plate curves always begins with a target print characteristic, i.e. what you want to achieve on press. This is called the target curve - the current tone reproduction that you wish to achieve. It could be your current press work, a proof, or it could be an industry supplied set of tone values. You measure the target sample and enter the dot area (tonal value) for the tints achieved on the target curve graph. If the target is a press sheet, for example, your current 150 lpi AM/XM presswork, the graph will represent your current tone print characteristic:
Target print characteristic tone curve - what we want our presswork to look like.

If you change your screening, for example going to FM screening, higher solid ink densities, or higher lpi AM/XM screening, etc. then, if nothing else changes, the tonal response on press will change due to the difference in dot gain:
New print characteristic tone curve caused by a change in screening method being used - what the presswork now looks like after changing the halftone screening.

The goal of implementing dot gain compensation plate curves is to make the new press work mimic the original target press tone response. In the above example, the boy's face should appear the same as the original image despite the dot gain caused by changing the halftone screening.

Creating the dot gain compensation plate curve

Building a dot gain compensation plate curve starts with comparing the current target tone response with the tone response of the new presswork. In this case run to the same solid ink densities, on the same paper and press - only the screening has been changed:
On the left is the current target tone curve and on the right is the new tone response resulting from the change in screening.

The graphs are then examined by looking at the original requested Postscript tone and the target response (left chart) and comparing it with the new tone response (right chart):
In the current target tone curve a 50% tone request resulted in a 68% tone in the presswork. That same target 68% was delivered in the new presswork from a requested tone value of 30%.

Put another way, we are looking for what requested tone value in our new presswork delivered the same final tone value in the target presswork. In this example a 30% tone request in the new presswork delivered the same tone value as a 50% request in the old while a 50% request in the new gave the same tone as a 70% request in the old.

Here's another way to visualize it:
Target 150 lpi compared with FM tone response.

Remapping the tones is simply doing this:
Find the tone in the new presswork that delivers the required tone response in the old target presswork.


The comparison between target curve and new current curve is made for each 10% change in tone.

The idea is then to map these values so that a tone request in the original file gets changed to a new value that produces the same final tone as the same tone request did in the old target presswork. The result is a lookup table for tone swapping.

In this example:

The requested 10% tone is remapped to request for a 4% tone
The requested 20% tone is remapped to request for a 10% tone
The requested 30% tone is remapped to request for a 18% tone
The requested 40% tone is remapped to request for a 24% tone
The requested 50% tone is remapped to request for a 30% tone
The requested 60% tone is remapped to request for a 40% tone
The requested 70% tone is remapped to request for a 50% tone
The requested 80% tone is remapped to request for a 65% tone
The requested 90% tone is remapped to request for a 80% tone

The lookup table creates the dot gain compensation plate curve.
The lookup table is applied in the workflow to remap the requested tones to the actual tones on plate that will deliver the desired final tones in the presswork. The result is tonal alignment of the presswork despite differences in dot gain.
On the left is the original target 150 lpi tone response. On the right is the "normalized" tone response of the FM screen.

Some points to keep in mind

1 - It does not matter if the plates are initially run "uncalibrated" or linear for the target presswork.
2 - A dot gain compensation plate curve is not usually applied to the tone range from 0%-5% and 95% to 100%.
3 - One dot gain compensation plate curve is usually applied to all process colors.
4 - There may be a need to apply a specific dot gain compensation plate curve to one of the process colors to maintain gray balance.
5 - Dot gain compensation plate curves cannot compensate for differences in gamut between FM/Stochastic screens and conventional AM/XM screens.

Friday, February 12, 2010

The lumbering print industry

During my tenure at Creo Inc. I was sometimes called upon to speak to newly hired engineers about print manufacturing to help them better understand the culture and conditions of the print industry. Now, engineers tend to be a very logical, pragmatic crowd. They are involved in the design and manufacture of almost everything, from cars to computers, from web pages to wings, from microchips to mobile phones so they do know quite a bit about manufacturing processes. But this is the print industry after all. So, to help them grasp some key concepts, I would often use an analogy. Analogies also fit comfortably within the time allotment of the three story elevator speech that is often used as the benchmark of a well articulated story. Keep it high-level, succinct, and to the point otherwise the engineer's eyes may glaze over and their minds wander on to other topics.

My talk would often go something like this:

Entering the elevator – So, what is print manufacturing all about? Well, imagine the printer as a lumber mill – a very special lumber mill. This is a lumber mill that doesn't govern what logs are acceptable for processing. Imagine that the logs were sometimes solicited by sales people and at other times by artists and other creative types. You'd receive anything vaguely shaped like a tree - dead wood, rotten wood, green twisted wood, phone poles, and non-wood poles painted to look like trees. Before you were allowed to process the "logs" you would have to win a competitive bid based on your ability to deliver the finished wood products - without actually knowing what your customer understands by the term "finished wood products" nor which of the possible variations on a log you will be receiving. To help communicate with your customer, you would use a "proof" – a simulation of the finished wood product that you will deliver. Of course, the proof simulation of your products actually uses another lumber mill's equipment but at least it consumes a copy of the "log" your customer has supplied to you. Unless, that is, the customer-supplied log breaks the equipment and doesn't actually get processed. In which case you either return the log to the customer to be rendered more log-like or you take on the task yourself without actually being able to charge for the log refining service.

What we do is supply those special lumber mills (read: printers) the tools to make the incoming "logs" (read: files) more log-like as well as the equipment to process the logs into acceptable finished goods which the lumber mill will be able to deliver at a profit margin sufficient for us to extract a small but valued portion.

Ah! This is our floor. Be seeing you. :-)

Another batch of files being delivered to the printer.

Wednesday, February 10, 2010

Why use halftone screen angles?

Go back in the history of halftoning and you'll discover that for multi-color presswork the halftone screens were always angled relative to one another. Why not just have all the screens at the same angle and be done with it? Well, when halftone dots are at the same frequency and angle then they will either print on top of each other (dot on dot)or they will print partially overlappingor they will print beside each other (dot off dot).
When dots print on top of dots you have wet ink sticking to wet ink (wet trapping) and white spaces between the dots. When dots print beside dots you have wet ink sticking to dry paper (dry trapping) with less white spaces between the dots. What does that mean? If you look at the images above you'll see that the dot on dot color looks darker and less vibrant than the dot off dot. The result is that the final blue hue, in this example, of dot on dot will also be different than the dot off dot blue because wet trapping inks reduces the ink's efficiency at filtering light. The white paper surrounding the dots also contaminates the perceived color by adding a graying effect and therefore the dot on dot printing will have less chroma (vibrancy) than the dot off dot.

The biggest issue though is that when there is slight misregistration on press the screen will shift from dot on dot to dot off dot causing the presswork to shift color and tone dramatically. However, by rotating the screens relative to one another, this wet trap/dry trap effect is randomized and therefore the color becomes more consistent when slight misregistration occurs.

The second major issue that occurs if all the screens in an AM/XM halftone have the same angle is that of moiré. Here, one of the colors has been slightly rotated - perhaps because of a small imaging problem, or because of a small press problem.
When this happens a very strong moiré appears when all colors have the same angle. However, by rotating the screens so that they are 30 degrees apart, there is some tolerance for small angle errors and moiré will not appear.

Using rotated screen angles for AM/XM halftones overcomes the dot on dot/dot off dot issues.
With FM/Stochastic screening, the same problems are overcome by using a different screen pattern for each of the process colors.

Sunday, February 7, 2010

The Wayback View – Rust in Peace

Just 7km/4.5 miles south of the city of Duncan and 53km/33 miles north of Victoria on Vancouver Island is Whippletree Junction - a grouping of specialty shops and restaurants set within 14 restored buildings from the early 1900s.Behind one of those buildings are the rusting remains of a typographic classic. It's an Intertype hot metal typesetting machine, most likely the very popular model C.
In 1911, New York newspaperman Hermann Ridder collected $4,000,000 in capital and organized the International Typesetting Machine Company. Several Linotype engineers joined the effort since it is believed that some Linotype people were disgruntled and felt they could produce a better machine. Since the early years, Intertype boasted a simpler design with fewer, but more standardized, parts than the Linotype. In fact, it was advertised that any standard Intertype part would fit any standard Intertype machine regardless of its age.

By late 1912, the company expanded their operating space to 80,000 square feet and employed in the neighborhood of 750 persons. The first machine was installed for a price of $2150 at the New York Journal of Commerce.
An Intertype ad from 1913

Intertype machines were so well engineered that they are still in productive use today as this one in Holland demonstrates.
video
Click play arrow (and maybe wiggle the play head), to view the video.

They are mainly used to produce people's names on slugs which are then used to personalise pencils, pencil cases, bookmarks, etc. with gold blocking.

In the UK, Express Gifts, part of Findel PLC, also uses Intertype C4s to produce slugs of people's names to manufacture personalised gift items. However these are computer driven by Decitek Floppy Disk Drives operating a Fairchild Teletypesetting unit.
video
Click play arrow (and maybe wiggle the play head), to view the video.

For more information regarding the early days of typesetting please visit "Metal Type" by clicking HERE

Special thanks go out to Trevor Bruckshaw for his help with research for this post.

Thursday, February 4, 2010

Avatar, iPad, and the future of the book

Amazing, but, in the future world of Avatar circa 2154 way out 4.4 light years from Earth, according to James Cameron, with all the high technology - when it comes to the important things and to knowledge transfer - it's not an iPad, it's still the printed (very thick) book - ink on paper - that is used as the key reference source as is shown in this very short scene from the movie:
video
Click play arrow (and maybe wiggle the play head), to view the short video clip from the movie.

Wednesday, February 3, 2010

Putting a glow in your presswork - OBAs and black light posters

Most printers who are faced with a printing job that's intended to glow under black light tend to think only about the issues of printing with fluorescent inks (see the post HERE). However, there is another important item that needs to be considered and that is the effect that the amount of, or lack, of OBAs (Optical Brightening Agents) in the paper will have on the final result.

For example, viewed under a black light this poster "glows" in an expected way:And it will look similar, except for the glow effect, under normal room and black light conditions.

However this poster which has large areas of white, i.e. unprinted paper, looks very different under normal house light:compared with being viewed under black light:
The difference in appearance is caused by the amount of OBAs in the paper. In this example, the paper contains low/no OBAs. Under normal home lighting the paper looks white and the fluorescent inks fairly bright. However, under black light the inks glow brightly but the paper which contains low/no levels of fluorescing agents goes dark - there is effectively no light for the paper to reflect.

This difference in color response can be used creatively or it could destroy the intended look of the poster as envisioned by the artist.
If a paper with high levels of OBAs is used instead, then the appearance of the image would be preserved under black light:
So, when quoting a "black light" job consider the amount of OBAs that the paper contains because it can have a profound effect on the final result. If the paper will have 100% ink coverage then choose a paper with high OBA content to assist in the final glow effect. If the design includes areas of white, then discuss the issue with the original designer and choose a paper that has high, or no OBA, content according to the final result the designer is trying to achieve.

To determine the relative amount of OBAs in the paper, view a sample using an inexpensive fluorescent type black light: