Tuesday, July 20, 2010
Wednesday, July 7, 2010
The Color Bar
Color bars (a.k.a. color control bars, color control strips, or proofing bars) are essentially test targets that are used to measure print and/or proof attributes. Normally, but not always, it is printed in the trim area of the press sheet.
Typical placement of a color bar on an offset press sheet - at the trailing edge (back end of the sheet).
However, it can take many different forms - sometimes hard to recognize - but always serving the same purpose.
Sometimes the "color bar" is incorporated within the graphic design of the publication. In this case the color makeup of the title (Cyan) and section headers (Blue, in this example, - Magenta overprinting Cyan).
Sometimes it is hidden in the spine (in this case the grey line running from top to bottom on the front edge of the photo).
While it is certainly possible to measure the color of the actual live image area, the technology is expensive and, as result, few printers are fortunate enough to have it at their disposal. Also, measuring the live image area doesn't provide as much useful information as a color bar can. Color bars therefore act as proxies, or substitutes, for the live image area as well as provide additional data.
The logic behind color bars
1) Unlike the live image area of the press sheet, color bars are consistent job to job. Therefore they are more efficient at providing a benchmark and can be used to track trends in variation over time.
2) Color bars can be tailored to meet the needs and measurement capabilities of individual print shops.
3) Color bars may be used to measure all aspects of the "print characteristic" - solid ink density, overprinting (ink trapping), dot gain, grey balance, as well as issues such as slur and dot doubling.
4) Color bars can reveal issues with ink hue, blanket condition, impression cylinder pressure, etc.
5) They can be used forensically to help understand why a specific job did not meet expectations.
6) They are efficient since, unlike the live image area, they are a constant made up of well defined elements that continue from proof to press sheet.
Solid ink density
A printing press is essentially a complex machine for laying down a specific film thickness of a specific color of ink onto a substrate. The ink is metered out in zones across the width of the press sheet according to how much ink coverage is required for each color in each zone.
Therefore, for most press operators, the minimum requirement for a color bar is that it contains solid patches of the inks that will be printing since solid ink density is the only thing on press that an operator can adjust while the press is running.
Those solid patches are then repeated over the width of the press sheet so that each ink zone is represented by at least one complete set of patches - containing one patch for each color being printed.
Information provided by only using solid ink density targets in the color bar
In this example, cyan is misregistered while the black printer is over emulsified (fountain solution breaking down the ink).
1) Provides a solid ink density value, measured using a densitometer, to determine if the press sheet is conforming to published industry, or shop specific targets.
2) Is an indirect, but practical, method of determining optimum ink film thickness and hence the balance of maximum color gamut without introducing image degrading inking issues such as slinging/misting.
3) The balance of the primary solid densities determines the hue of the overprints - i.e. the SID of magenta and SID of yellow determine the hue of the resulting red.
4) Indicate misregistration which can then be examined in the live image area.
5) Reveal defects such as slinging/misting/tailing, over emulsification, slur, doubling.
6) If records are kept, the hue of the ink currently on press compared with the hue of ink used in the past to determine if there is any contamination, change in color due to ink batch differences, etc.
Forensic targets on color bars are image elements that are typically not measured by the press operator unless there is a problem in aligning presswork to the proof. If that happens then these targets may provide useful information as to the cause of the problem.
Two-color overprint ink trapping targets
Ink "trap" is an objective indication of the ability, or inability, of a printed ink to accept the next ink printed compared with how well the substrate accepted that ink. Poor ink trapping results in presswork color shifts in reds (magenta plus yellow), greens (cyan plus yellow), and blues (cyan plus magenta) as well as a loss in total color gamut.
The two-color overprint solids allows for the objective measurement and evaluation of ink trap efficiency as well as the overprint hue error and greyness.
Typical trap values for three print conditions running a CMY ink sequence with Black first or last down:
Offset sheetfed: R=70, G=80, B=75
Heatset web offset (publications): R=70, G=87, B=72
Coldset web offset (newspaper): R=50, G=89, B=50
Slur and doubling targets
Slurring and doubling are print defects that occur when halftone dots and type blur as a result of a slight second contact or movement between press cylinders or the paper and blanket. (More about slur HERE and doubling HERE)
There are many different styles of slur and doubling detection targets. Here are two of the most popular:
Of course, every halftone dot or letter character on the printed sheet will reveal slur and doubling, however the targets in the color bar signal the defect easier and quicker.
Grey balance targets
Grey balance targets are made up of a patch of three screened process colors that are balanced so as to appear as neutral grey under standard printing conditions. They are typically printed adjacent to a black screen tint of a similar value to allow for a quick visual, or measured, evaluation of how grey balance has shifted.
Grey balance targets can be useful since variation in any of the three process colors because of dot gain, slur, doubling, density, trapping, and registration will be reflected by a shift in hue away from neutrality. The 3/C patch will take on a bluish, reddish, or greenish color cast.
The idea behind this target is that any grey balance color shift away from neutrality suggests a possible color shift in the live image area. However, in production printing the grey balance target may not be a reliable indicator of presswork issues.
Other targets
Other targets that may be included in the color bar are:
Dot gain
These targets are intended to capture dot gain variation information. The dot gain targets may consist of just two patches for each process color to measure the dot gain a one location on the tone scale, or, with the addition of more patches, to measure the dot gain at the quarter, mid, and three-quarter tone values. Dot gain can be useful because issues like slur, doubling, or incorrect solid ink density, will be reflected by a variation in the measured dot gain.
Brown balance targets
Brown balance patches are similar to grey balance patches in function except that they are made up equal percentages of cyan, magenta, and yellow. Unlike grey balance patches which allow the press operator to make a subjective visual assessment of hue shift, brown balance patches can only be evaluated objectively with instruments.
Proprietary
Proprietary targets such as that used by System Brunner are typically used to drive on-press closed loop color control systems.
Spot color
If a spot or brand color is being used then it will warrant at least a solid patch in the color bar so that its solid ink density can be measured. Space permitting, the solid patch will be adjacent to a screened back patch so that dot gain information can be measured.
For process control, color bars should be included on every proof and press form of every job. If that is not possible because there is no room on the sheet (as often happens in newspaper work) then there are several options;
1) Run color bars on occasion by including it in the live image area.
With the publisher's permission if required.
2) With the print buyer's permission, incorporate color bars test elements into the graphic/editorial design of the printed piece (see the USA Today example in Part 1).
Color bars are not a requirement for quality printing, however, they are key to making proofing and printing more efficient and effective while reducing overall production costs.
Presswork should be run "to the numbers" i.e. the solid ink density aim points, at which time the presswork should align to the signed-off proof. At that point the press operator should be free to make any needed ink key adjustments to refine the match. The color bar then becomes a record of initial match and needed adjustments. That information can be used in statistical process control to spot any trends, or issues, revealed by the kind of ink key moves that are made over time.
Color bars can be placed anywhere that they fit on the press form, including the lead and trailing edge as well as across the center of the form. In fact, placing it in the center of the form parallel to the inking rollers is ideal, since there is less likelihood of seeing the variation that occurs at the lead and trailing edges. Color bars can even be placed in the gutter inline with the direction of the sheet through the press, although doing so is not optimal since it provides information from only one ink key zone.
Ideally the color bar should use the same halftone screening as the live image area and have had the same press curve applied.
However, it can take many different forms - sometimes hard to recognize - but always serving the same purpose.
While it is certainly possible to measure the color of the actual live image area, the technology is expensive and, as result, few printers are fortunate enough to have it at their disposal. Also, measuring the live image area doesn't provide as much useful information as a color bar can. Color bars therefore act as proxies, or substitutes, for the live image area as well as provide additional data.
The logic behind color bars
1) Unlike the live image area of the press sheet, color bars are consistent job to job. Therefore they are more efficient at providing a benchmark and can be used to track trends in variation over time.
2) Color bars can be tailored to meet the needs and measurement capabilities of individual print shops.
3) Color bars may be used to measure all aspects of the "print characteristic" - solid ink density, overprinting (ink trapping), dot gain, grey balance, as well as issues such as slur and dot doubling.
4) Color bars can reveal issues with ink hue, blanket condition, impression cylinder pressure, etc.
5) They can be used forensically to help understand why a specific job did not meet expectations.
6) They are efficient since, unlike the live image area, they are a constant made up of well defined elements that continue from proof to press sheet.
Solid ink density
A printing press is essentially a complex machine for laying down a specific film thickness of a specific color of ink onto a substrate. The ink is metered out in zones across the width of the press sheet according to how much ink coverage is required for each color in each zone.
Therefore, for most press operators, the minimum requirement for a color bar is that it contains solid patches of the inks that will be printing since solid ink density is the only thing on press that an operator can adjust while the press is running.
Those solid patches are then repeated over the width of the press sheet so that each ink zone is represented by at least one complete set of patches - containing one patch for each color being printed.
Information provided by only using solid ink density targets in the color bar
1) Provides a solid ink density value, measured using a densitometer, to determine if the press sheet is conforming to published industry, or shop specific targets.
2) Is an indirect, but practical, method of determining optimum ink film thickness and hence the balance of maximum color gamut without introducing image degrading inking issues such as slinging/misting.
3) The balance of the primary solid densities determines the hue of the overprints - i.e. the SID of magenta and SID of yellow determine the hue of the resulting red.
4) Indicate misregistration which can then be examined in the live image area.
5) Reveal defects such as slinging/misting/tailing, over emulsification, slur, doubling.
6) If records are kept, the hue of the ink currently on press compared with the hue of ink used in the past to determine if there is any contamination, change in color due to ink batch differences, etc.
Forensic targets on color bars are image elements that are typically not measured by the press operator unless there is a problem in aligning presswork to the proof. If that happens then these targets may provide useful information as to the cause of the problem.
Two-color overprint ink trapping targets
Ink "trap" is an objective indication of the ability, or inability, of a printed ink to accept the next ink printed compared with how well the substrate accepted that ink. Poor ink trapping results in presswork color shifts in reds (magenta plus yellow), greens (cyan plus yellow), and blues (cyan plus magenta) as well as a loss in total color gamut.
The two-color overprint solids allows for the objective measurement and evaluation of ink trap efficiency as well as the overprint hue error and greyness.
Typical trap values for three print conditions running a CMY ink sequence with Black first or last down:
Offset sheetfed: R=70, G=80, B=75
Heatset web offset (publications): R=70, G=87, B=72
Coldset web offset (newspaper): R=50, G=89, B=50
Slur and doubling targets
Slurring and doubling are print defects that occur when halftone dots and type blur as a result of a slight second contact or movement between press cylinders or the paper and blanket. (More about slur HERE and doubling HERE)
There are many different styles of slur and doubling detection targets. Here are two of the most popular:
Of course, every halftone dot or letter character on the printed sheet will reveal slur and doubling, however the targets in the color bar signal the defect easier and quicker.
Grey balance targets
Grey balance targets are made up of a patch of three screened process colors that are balanced so as to appear as neutral grey under standard printing conditions. They are typically printed adjacent to a black screen tint of a similar value to allow for a quick visual, or measured, evaluation of how grey balance has shifted.
Grey balance targets can be useful since variation in any of the three process colors because of dot gain, slur, doubling, density, trapping, and registration will be reflected by a shift in hue away from neutrality. The 3/C patch will take on a bluish, reddish, or greenish color cast.
The idea behind this target is that any grey balance color shift away from neutrality suggests a possible color shift in the live image area. However, in production printing the grey balance target may not be a reliable indicator of presswork issues.Other targets
Other targets that may be included in the color bar are:
Dot gain
These targets are intended to capture dot gain variation information. The dot gain targets may consist of just two patches for each process color to measure the dot gain a one location on the tone scale, or, with the addition of more patches, to measure the dot gain at the quarter, mid, and three-quarter tone values. Dot gain can be useful because issues like slur, doubling, or incorrect solid ink density, will be reflected by a variation in the measured dot gain.Brown balance targets
Brown balance patches are similar to grey balance patches in function except that they are made up equal percentages of cyan, magenta, and yellow. Unlike grey balance patches which allow the press operator to make a subjective visual assessment of hue shift, brown balance patches can only be evaluated objectively with instruments.Proprietary
Proprietary targets such as that used by System Brunner are typically used to drive on-press closed loop color control systems.Spot color
If a spot or brand color is being used then it will warrant at least a solid patch in the color bar so that its solid ink density can be measured. Space permitting, the solid patch will be adjacent to a screened back patch so that dot gain information can be measured.For process control, color bars should be included on every proof and press form of every job. If that is not possible because there is no room on the sheet (as often happens in newspaper work) then there are several options;
1) Run color bars on occasion by including it in the live image area.
With the publisher's permission if required.2) With the print buyer's permission, incorporate color bars test elements into the graphic/editorial design of the printed piece (see the USA Today example in Part 1).
Color bars are not a requirement for quality printing, however, they are key to making proofing and printing more efficient and effective while reducing overall production costs.
Presswork should be run "to the numbers" i.e. the solid ink density aim points, at which time the presswork should align to the signed-off proof. At that point the press operator should be free to make any needed ink key adjustments to refine the match. The color bar then becomes a record of initial match and needed adjustments. That information can be used in statistical process control to spot any trends, or issues, revealed by the kind of ink key moves that are made over time.
Color bars can be placed anywhere that they fit on the press form, including the lead and trailing edge as well as across the center of the form. In fact, placing it in the center of the form parallel to the inking rollers is ideal, since there is less likelihood of seeing the variation that occurs at the lead and trailing edges. Color bars can even be placed in the gutter inline with the direction of the sheet through the press, although doing so is not optimal since it provides information from only one ink key zone.
Ideally the color bar should use the same halftone screening as the live image area and have had the same press curve applied.
Friday, July 2, 2010
The Wayback View – Making a newspaper - 1944
The making of the Star Journal and Minneapolis Tribune newspaper from original art to final presswork.
Preview images from the video
Please press the play arrow to view the video. Note that it may stop for a moment while the video buffers in the background.
Today's Star Tribune is the product of the merger in 1982 between the Minneapolis Star, an evening newspaper, and the Minneapolis Tribune, a morning newspaper published by the same company.
In March 2007 Par Ridder was named Publisher of the Star Tribune, after his predecessor, J. Keith Moyer, decided to leave the newspaper after the sale to private-equity firm Avista Capital Partners. Ridder, who resigned on December 7, 2007 is a member of the Ridder family that had owned Knight-Ridder, the publishers of several newspapers including the rival Saint Paul Pioneer Press. Ridder's arrival resulted in considerable litigation when it was discovered that he had stolen a hard drive which was Pioneer Press property. This hard drive was laden with information about employees and advertisers which the Pioneer Press characterized as "trade secrets". Ridder also took two high-ranking staff members with him to the Minneapolis paper.
On January 15, 2009, as the nation's 15th largest daily paper, the paper filed for Chapter 11 bankruptcy.
Please press the play arrow to view the video. Note that it may stop for a moment while the video buffers in the background.
Today's Star Tribune is the product of the merger in 1982 between the Minneapolis Star, an evening newspaper, and the Minneapolis Tribune, a morning newspaper published by the same company.
In March 2007 Par Ridder was named Publisher of the Star Tribune, after his predecessor, J. Keith Moyer, decided to leave the newspaper after the sale to private-equity firm Avista Capital Partners. Ridder, who resigned on December 7, 2007 is a member of the Ridder family that had owned Knight-Ridder, the publishers of several newspapers including the rival Saint Paul Pioneer Press. Ridder's arrival resulted in considerable litigation when it was discovered that he had stolen a hard drive which was Pioneer Press property. This hard drive was laden with information about employees and advertisers which the Pioneer Press characterized as "trade secrets". Ridder also took two high-ranking staff members with him to the Minneapolis paper.
On January 15, 2009, as the nation's 15th largest daily paper, the paper filed for Chapter 11 bankruptcy.
Tuesday, June 29, 2010
You can take it with you! - (How to be at the printshop - when you're not.)
Sometimes you just can't be at the printshop. Perhaps you're on holidays, relaxing at home in the evening, or maybe just goofing off on a "customer visit." Well now there's a way to not be away when you're away: just carry the sounds of the pressroom with you.
You can play them when you're pining for the shop when traveling to remind you of how good your job is:
The chugga chugga of a Heidelberg press
Or simply play them in the background when you get that unexpected phone call from the boss:
The satisfying rhythm of a productive press
You can acquire the appropriate press sounds that meet your shop's equipment from the online sound effects library HERE to use and enjoy as needed.
You can play them when you're pining for the shop when traveling to remind you of how good your job is:
The chugga chugga of a Heidelberg press
Or simply play them in the background when you get that unexpected phone call from the boss:
The satisfying rhythm of a productive press
You can acquire the appropriate press sounds that meet your shop's equipment from the online sound effects library HERE to use and enjoy as needed.
Sunday, June 6, 2010
Implementing FM Screening
The foundations of successful FM screening implementation include the following steps:1) Make sure that everyone in the shop that is involved with print sales and production understands why the company is changing the print process. All should want the change to succeed and should see a payback specific to their area. Sales will have a new story to tell about the company's ability to meet buyer expectations. Prepress and pressroom will be able to stabilize and optimize their areas. Management should see a clear differentiator, reduced manufacturing costs and more consistent product.
2) Make sure that the plates have the resolution to support FM at the chosen micron size (typically 20-25 micron for general commercial, 25-35 micron for publications and newsprint). Contact your local service or sales representative for the current list of qualified media.
3) Make sure that your CtP has the capability to do FM at the chosen micron size. Again, contact your local service or sales representative.
4) Communicate your intent to print FM with your ink vendor. Ask them about the ink series you are using and whether it is appropriate for FM. They may suggest a different series based on their experience. If they don't have experience with FM, then involve them in your initial start up and learning. If they are not interested then start looking for a different ink vendor.
5) Your shop should have an existing reliable and consistent print manufacturing process. I.e. the press is not used as a color correction device. One simple test is to have the press operator do their make ready without seeing a proof. In a well run shop, the press can be brought up to color and when then compared to the proof there will be very little difference. If the press operator is lost without the proof then that might indicate that the process is not stable and in control.
6) Build dot gain curves to be applied to plate imaging to bring tone reproduction in line with your current AM/XM printing.
7) Optionally, fine tune your proofing so that it reflects the extra gamut you'll see with FM.
8) Make FM your standard screening - not an exception for special projects. The goal should be that AM/XM screening only be used for special applications like reprints. That way the press operator gain experience and understanding of how FM reacts on press compared to what they are currently familiar with.
9) If you have more than one press/press crew - choose one to be your pioneers and champions of FM printing. They can then teach the other crews the keys to their success.
Generally, most of the problems encountered with implementing FM screening result from print shop culture - not the technology itself.
Fountain Solutions
Due to the over all small dot sizes, ink and water balance is more critical with FM screening (and very high lpi AM/XM screening) than with conventional AM/XM screens at industry standard lpis. So, before switching to FM screening, you should resolve any ink and water issues you have with your current screens.There are no set rules about fountain solutions and FM, except to use a good product that is recommended by your ink and plate manufacturer. In general, less is best. Where possible, run the minimum dosage in your fountain solutions that the manufacturer recommends.
While FM microdots are less sensitive to physical dot gain from over-inking, they are more sensitive than the larger AM/XM dots to surrounding water levels and fountain conditions. Therefore, it is important to control pH, temperature, conductivity, and contamination in the water pick-up tray and on the chrome or ceramic pick-up rollers. The temperature of the fountain can be controlled in the re-circulation system (keep in mind that temperature in the tray may be 5 to 10 degrees warmer). Fountain temperature should be controlled within 0-5 degrees of manufacturer’s specification. Temperature can be further controlled in the press, using chilled rollers. Buffered fountain solutions help to stablize pH levels; however, pH should still be measured periodically to ensure that it stays within the manufacturer’s specifications. Processed water is recommended to further stabilize conductivity and pH. Check with your supplier to find a water treatment system suited to your printing needs.
A certain level of ink contamination in the fountain is unavoidable; however, excessive contamination is an indicator of other issues. In fact, it may first be noticed in your presswork as all-color "rain," or water streaking. Look for excess ink coming back through the roller train. This is sometimes referred to as chrome roller feedback, pick-up, ink belled back or reverse emulsification. Numerous factors affect this condition, including temperature of ink and fountains, emulsification, press speed, and the condition of the water pick-up roller. Simple remedies include better maintenance of chrome roller surface (no micro-cracks), temperature control, and desensitizing the chrome roller to improve the water pickup and keep ink away.
Back trap piling in the non-image area of the plate or blanket is generally caused by excessive ink in the fountain, low conductivity, and non-image area that is not desensitized – attracting ink instead of repelling it with water. Remember that fountain solution is a mild solvent. As such, if it is over aggressive it may overpower the ink film on the microdots and cause a loss of ink density.
Alcohol and alcohol substitutes help lower surface tension and ink viscosity, which promotes better release of FM's microdots. The amount of alcohol and alcohol substitutes used will depend on environmental restrictions in each locale.
When implementing FM screening it sometimes helps to view the screening in the context of AM/XM halftoning. There are two basic ways to look at how they compare.The first is related to their resolution, or detail rendering equivalency. That is usually determined by running a line diagonally through the FM screen and then measuring the number of dots per inch along that line. The more dots per inch that the line intersects the higher the effective lpi.
The second is their lithographic equivalency. Basically how the FM screen reacts on press to ink, water, etc. That is usually determined by counting the number of transitions (dot edges) in a given screen tone area and comparing that to the number of transitions in the same tone area in an AM screen.
Here are the numbers for several popular FM dot sizes - micron size compared to lpi:
Detail rendering equivalency:
FM 20 = 500 lpi
FM 25 = 325 lpi
FM 35 = 325 lpi
FM 36 = 275 lpi
Lithographic equivalency:
FM 20 = 385 lpi
FM 25 = 240 lpi
FM 35 = 240 lpi
FM 36 = 205 lpi
The above equivalencies are for a typical second order FM screen - one that, close up, looks like this:
The vast majority of FM screens in use today are second order using similar dot patterns so the equivalencies should be close enough for practical application. These equivalents are not absolute values since they will differ somewhat according to the design of the specific screen and how the engineer calculates equivalency.
Curve Management
The dot gain characteristics of FM require the application of dot gain compensation curves to plates. For predictable tonal response on press, keep the mechanical and chemical conditions on your press well maintained, and only build tonal compensation curves when the press is in a stable condition for your current AM/XM printing.
The basics of building tonal compensation curves to align your AM and FM presswork
1. This will take two press runs - one to get data for your current screening, and the second to get the response of the FM screening. If you have confidence in your current AM/XM presswork you may choose to only do the FM screening pressrun and compare the values it delivers to the target tones of your AM/XM presswork.
2. Your press should be in a stable condition that accurately reflects your pressroom environment, including documented standard ink density (SID) for your shop.
3. Your existing AM/XM presswork should be the tonal target for your FM screened presswork.
4. Image plates for your AM screening using whatever plate curves you currently apply.
5. Image plates for your FM screening without applying any plate curves (uncalibrated plate).
6. Bring your presswork to to standard solid ink densities.
7. Pull several good sheets and measure the CMYK tone scale response of the AM/XM and FM screens. The more sheets you
measure, the more representative the average will be of your printing conditions.
8. Use the measured data to build tonal compensation curves for your FM presswork.
9. Set up your RIP and workflow to manage the application of the FM curves.
10. Create and impose a test target for you FM presswork to confirm that the workflow has image the plate with the correct dot gain compensation curve.
11. Go back on press for a verification run to confirm that the curves for the FM screening are correct. Make adjustments as required.
Color Management
You may optionally decide to profile your FM presswork in order to reflect the added FM gamut so that your proofs are a closer match to your presswork.
1. To color manage a proofing device, build profiles by characterizing your FM presswork proofs with ICC targets or equivalent.
2. Gather the characterization data from your FM verification press run and use the resulting measurements to build an ICC profile to be used in a color-managed workflow to drive your proofer.
3. This is rarely done, however, if desired, you may choose to build a separation profile to convert RGB images to CMYK in order to take advantage of FM screening's larger gamut.
Image Management
1. When printing with FM 20 or FM 10 on coated paper on sheetfed and web presses, scan at resolutions above 300 dpi to take advantage of FM's ability to render and capture very fine details and texture. There is no need to scan higher than 600 dpi.
2. When printing newsprint with FM 36 or FM 25, you do not need to scan images higher than 300 dpi. Typically, images may be scanned at resolutions as low as 150 to 200 dpi. To determine the lowest resolution at which you could scan images and print successfully, do a press test. When the resolution is too low, you may see stair casing around the edges of image objects.
3. Make sure that images are not down sampled when going from native file applications to PDF.
4. Make sure that there are no settings in the RIP that will cause images to be resampled at a lower resolution.The Pressroom
Presses
Older coldset webs may have problems with FM screens and AM/XM screens finer than 110 lpi. Dampening systems running bareback with a durometer reading harder than 34 may have difficulty running FM.
Older presses with conventional dampening systems that use covers, sleeves, socks and/or wraps anywhere in the system may find that the increased detail resolution of FM results in the fabric weave/grain of the dampener material being resolved on the press sheet.
Older webs that can run 133 lpi screens can run 35 micron FM and coarser, while older webs than can run 150 lpi screens can run 25 micron FM and coarser. Older webs without an in-feed can also run 35 micron FM. In-feeds are important for web control and can reduce plate wear, web movement, and linting.
On newspaper webs, printing on paper with a recycled content of 75% or greater may create problems because the paper carries a high amount of silica, which causes piling and plate blinding.
InkFor all press types, before using FM screens, speak with your ink supplier as they may have identified an ink series that works best with this type of screening. Remember that it is not so much whether the screening is AM/XM or FM that's important, it's the size of the dots through the tone scale that helps determine the formulation and performance of the ink.
When using 25 micron FM, you should be printing with inks that flow well with 133 line AM screens, and, for 20 micron FM you should be printing with inks that flow well with 175 line AM screens.
Ideally, FM inks should have low viscosity and high flow. Low viscosity helps ink shear and transfer to the sheet. Printers can drop viscosity by changing the pigment vehicle (oil), by increasing the water pickup, or by increasing ink temperature. High-pigment, low-gain inks are problematic with FM screening because they have a propensity to pile and print inconsistently.
Remember that each press is different. Settings and inks that work well on one press may not work well on another press.
1. Use progressive-tack as opposed to common-tack inks for FM. Generally, you do not need to change ink tack values or sequence from those used with AM/XM settings.
2. Metallic and fluorescent inks have poor transfer, even with conventional 175 lpi screens. The pigments in these inks are coarse, and little can be done to improve the vehicle. Coarser screens such as 25 or 35 micron FM are better suited to these inks. Check with your ink manufacturer to see what other options are available.
3. Some PMS colors (spot or special color) lead to inconsistent coverage on sheetfed presses. For example, solid tints can appear mottled or look like the texture of an orange peel, and this can impact FM screen tint builds. The pigment in each PMS color can vary considerably therefore you should work your ink manufacturer to optimize performance for the dot size you are printing with. If mottle occurs, it may be necessary to mill/refine/grind the ink a second time to reduce the size of the pigment particles.
4. FM performs best on press when using lower levels of water and just enough ink to achieve desired densities. Use water levels rather than ink density to control FM microdots. Adjusting density to control midtones should be the exception and not common practice with FM.
5. Generally speaking, 175 lpi sheetfed printers are typically well suited to run 20 micron FM with the inks they use for their AM/XM printing; however, these printers may still need to adjust ink flow and viscosity to optimize the ink for FM’s microdots.
6. Use low-viscosity, high-flow inks for heat-set webs. Chilled or water-cooled oscillators keep roller temperatures constant and maintain ink viscosity and performance at ideal levels. If your press doesn’t have this capability, ask your ink manufacturer to help change viscosity by altering water pickup or oil.
7. On web presses, use process black ink instead of book black inks where possible. Process black ink
offers the best results with FM as it behaves like cyan, magenta, and yellow inks.
8. On heat- and cold-set webs, book black and recycled black inks have poor transfer rates, and they behave more like fluorescent and metallic ink. Book black ink is typically used for high-density requirements while recycled, black ink is used in high-volume applications such as publications, newspaper, flexography, and packaging to meet cost and environmental requirements.
9. Heat-set and cold-set web inks are generally suitable for 25 and 36 micron FM and typically do not require changes to formulation or vehicle.
10. For 20 micron FM on web presses, work with your ink manufacturer to optimize performance.
Undesirable Patterns in Presswork
Proper press maintenance should be the policy no matter what halftone screening is being used. However, the finer the screen the more critical proper maintenance becomes since the microdots used in high lpi AM/XM and FM screens can reveal flaws in the presswork that were previously hidden by large AM dots. Thin Lines in the presswork
Flaws and grind lines on press rollers can cause visible lines to appear in press work when printing with fine AM/XM and FM screens. They are characteristically oriented in the direction of paper travel through the press.
Grind lines are imperfections in the rubber rollers caused by grinding in manufacturing and wear on press. They show up as dark lines in the direction of paper travel with a frequency of one to four millimeters. They can be seen by using a loupe and examinging the solids. They are sometimes visible to the eye between the 50% and 75% FM tints. When water film on press is too thin to fill the grind and wear lines on rubber rollers, the resulting water film is uneven and transferred to the plate. Under 200 lpi, the uneven water film has little effect. However, finer screens can render inconsistencies in the water film, and these flaws show up as thin, dark lines in the presswork.
Roller grind lines are typically found on the water, form, or metering rollers. You can visually monitor the quality of water film by examining your chrome rollers and by examining your presswork. When there are visible fine lines and patterns on the chrome rollers, you have inconsistent water transfer, and the source can be either roller grind lines or overly sensitized rollers. White and milky water film on chrome rollers can identify overly sensitized rollers and can indicate that the rollers need desensitizing to help water move smoothly through the press. Ask your press and/or ink vendor for a suitable desensitizing agent.
Short thin "rain—lines" that vary over the sheet and from sheet to sheet may be caused by water lines. They can be found in solids and screen tints and look somewhat like a rainstorm. When water lines are dark, look for ink/water emulsification problems. When water lines are light (looks like lots of short scratches), water and ink levels are generally too low.
Micro patterning and micro detail
FM screening can resolve both desirable detail in images as well as undesirable detail created at various stages in the reproduction process. In particular, fine artifacts such as photographic grain, paper texture, and image manipulation artifacts may not show up with 150 lpi screens but may be resolved with AM/XM and FM microdots. Careful analysis by measuring the pattern, frequency, and angle of micro structures can help identify whether the source is screening, imaging, processing, or presswork. Rotating the plates and images can also help to narrow down the sources of unwanted patterns.
Mottle
Mottle results in botchy, uneven, flat tints with an orange peel texture and is most evident when you look at solids under a loupe. Mottle may be caused by ink breaking down making solids appear as if the were printed with flexography. It is most commonly seen in Pantone Matching System colors with coarsely ground pigments. It’s also common with high pigment loads when emulsification leads to uneven ink films being transferred to the sheet. Low water levels can cause PMS colors to bleed in FM tints, leading to excessive gain and further mottle. Flat-tint mottles are especially bad in blues, greens, and alkaline browns.
Mottle can also be caused by the substrate if it does not have a consistent ink accepting surface. Sometimes the paper's potential for mottle can be seen by holding the sheet up to a light and seeing if there is a blotchy quality of shiny and matte areas.
Run length
A few printers may experience shorter run lengths with FM screening on heat-set web presses (but not with positive plates or sheetfed presswork). This may be the result plate wear or blinding. On negative plates, calcium carbonate crystals from the paper (two to three microns in size) may accumulate on small dots and cause blinding - the plate image is visible on plate but does not carry ink. The smaller dots in both AM/XM and FM printing are also susceptible to paper piling, which can exacerbate plate wear or cause blinding on poorly maintained web presses.
Thursday, June 3, 2010
Toilet training - for the printer
When I worked at the graphics vendor Creo, one salesperson's test of a printshop's character was not its presswork or company motto but the state of its...toilets. It was the first part of the shop he would investigate.
His feeling was that printshops would start up at some time in the past with the best of intentions - everything spic and span, neat and tidy.
However, over time, familiarity, complacency, and laziness would invariably set in.
And no matter what high minded ideas management had for the company, the lowliest facility - the toilet - would reveal the true character of the shop. Toilets provided witness to the reality of the shop's true culture.
The company's toilets, after, were the one area shared by top management and lowest level employee - so blame could not be transferred.
So, it is critical that the company's toilet facilities be considered just as much of an ambassador of the company as any other part of the printshop's facilities.
The toilet facilities indeed reflect the company's attitude and vision for its business.
His feeling was that printshops would start up at some time in the past with the best of intentions - everything spic and span, neat and tidy.
However, over time, familiarity, complacency, and laziness would invariably set in.
And no matter what high minded ideas management had for the company, the lowliest facility - the toilet - would reveal the true character of the shop. Toilets provided witness to the reality of the shop's true culture.
The company's toilets, after, were the one area shared by top management and lowest level employee - so blame could not be transferred.
So, it is critical that the company's toilet facilities be considered just as much of an ambassador of the company as any other part of the printshop's facilities.
The toilet facilities indeed reflect the company's attitude and vision for its business.
Sunday, May 30, 2010
The issue of metamerism in print production
With print, each medium in the production process from original art to image capture, monitor display, proof, and final presswork has its own unique spectral characteristics. The majority of color reproductions utilize cyan, magenta, yellow, and black inks or colorants. But none of those inks are exact spectral matches to the media originally used to produce the original art. As a result, the inks used to create color reproductions are combined to simulate an artwork, but only under one industry standard light source - referred to as "D50" or "D65".
During production the integrity of the reproduction of artwork is monitored by making comparisons, for example, original to its copy or proof to presswork. The two colored objects are referred to as a metameric pair if they match under at least one combination of illuminant and observer and not match under at least one combination of illuminant and observer. They must also have different spectral response curves.
So, the phenomenon of metamerism begins with comparing a pair of colored objects. For example the color of the back door of this truck compared with the color of the rest of the truck.
In the truck example the pigments used in the paint were not the same for the back door compared with the rest of the truck. The two colors would have matched under the artificial lighting that was used when the door was painted. However, under sunlight conditions the door and body no longer match causing "metameric failure."
In this case metameric failure is a benefit to the prospective customer since it warned that the door was painted at a different time from the rest of the truck. Possibly it had been damaged and subsequently repaired. Unfortunately the effect of metameric failure in print production usually causes problems rather than benefits.
How metameric failure impacts print production
There are four types of metameric failure commonly encountered in print production.
Sample metameric failure This is the most common cause of color matching problems. The truck example above is an example of sample metamerism. Because proofs and press sheets form metameric pairs, this problem typically shows up when presswork matches the proof in the light booth at press but no longer match under the lighting conditions where the presswork will normally be used, e.g. a package in a store, or brochure in a home environment. Other examples of sample metameric failure include product samples (e.g. fabric) compared with their reproduction in proofs, presswork, or computer displays. Or process color screen tint builds. They may match under one lighting condition but not another. Sample metameric failure can also happen if two prints using very different technologies - such as offset print vs silkscreen print - are compared under different lighting conditions.
Observer metameric failure This can happen because of differences in color vision between observers. Although the common cause is colorblindness, it is not uncommon among "normal" observers. As a result, two spectrally dissimilar color surfaces may produce a color match for one person but fail to match when viewed by a another person. Observer metameric failure is the reason there were 31 individuals tested to derive the original 1931 "standard observer" values adopted by the ISO and that are still used today as the basis for the majority of color science.
Field-size metameric failure This occurs because the relative proportions of the three light sensitive cone types in the retina of the eye vary from the center of the visual field to the periphery. The result is that colors that match when viewed as very small, centrally fixated areas may appear different when presented as large color areas. This is the reason why color painted on a wall may appear different than the paint chip used to select the color even though they match when the chip is placed on the wall. In print production field-size metameric failure typically occurs when small PMS swatchbook samples are used to specify a PMS color that will cover a large press sheet area.
Geometric metameric failure Normally, material attributes such as translucency, gloss or surface texture are not considered in color matching. However here, identical colors appear different when viewed at different angles, distances, light positions, etc. Geometric metameric failure is most often seen when using metallic inks or paper, and specialty ink coatings or papers.
Tips for dealing with metameric failure
1. Be aware that it exists and may be the "simple" issue causing any color match issues.
2. If color needs to align across different lighting conditions choose pigments carefully or make the ink formulator aware of that requirement.
3. Control your lighting conditions - both for producing prints, final viewing (where possible), and for critical evaluation. The industry standard light source is referred to as "D50" or "D65" (5,000° Kelvin (North America), 6,500° (Europe).
4. Invest in PIA/GATF RHEM light indicators for everyone in the production chain that is involved in evaluating and approving color. RHEM light indicators are small (2" x 3/4") paper stickers with a unique printed design that uses metameric failure to indicate whether or not the viewing conditions are 5,000° K or not.
Stripes appearing in the RHEM sticker indicate the lighting conditions and therefore whether a color evaluation can be made.
The stickers can be affixed to proofs or simply carried in a protective wrapper in purse or wallet.
5. Printshops should have viewing areas away from the press that allow print customers to view the presswork under typical lighting conditions (fluorescent and incandescent).
6. Be sure that all instruments (e.g. spectrophotomers) that are used for color evaluation are set to the same standard illuminant, D50 or D65, and same observer angle (typically 2°).
What is wrong with this scene?
During production the integrity of the reproduction of artwork is monitored by making comparisons, for example, original to its copy or proof to presswork. The two colored objects are referred to as a metameric pair if they match under at least one combination of illuminant and observer and not match under at least one combination of illuminant and observer. They must also have different spectral response curves.
So, the phenomenon of metamerism begins with comparing a pair of colored objects. For example the color of the back door of this truck compared with the color of the rest of the truck.
In the truck example the pigments used in the paint were not the same for the back door compared with the rest of the truck. The two colors would have matched under the artificial lighting that was used when the door was painted. However, under sunlight conditions the door and body no longer match causing "metameric failure."
In this case metameric failure is a benefit to the prospective customer since it warned that the door was painted at a different time from the rest of the truck. Possibly it had been damaged and subsequently repaired. Unfortunately the effect of metameric failure in print production usually causes problems rather than benefits.
How metameric failure impacts print production
There are four types of metameric failure commonly encountered in print production.
Sample metameric failure This is the most common cause of color matching problems. The truck example above is an example of sample metamerism. Because proofs and press sheets form metameric pairs, this problem typically shows up when presswork matches the proof in the light booth at press but no longer match under the lighting conditions where the presswork will normally be used, e.g. a package in a store, or brochure in a home environment. Other examples of sample metameric failure include product samples (e.g. fabric) compared with their reproduction in proofs, presswork, or computer displays. Or process color screen tint builds. They may match under one lighting condition but not another. Sample metameric failure can also happen if two prints using very different technologies - such as offset print vs silkscreen print - are compared under different lighting conditions.
Observer metameric failure This can happen because of differences in color vision between observers. Although the common cause is colorblindness, it is not uncommon among "normal" observers. As a result, two spectrally dissimilar color surfaces may produce a color match for one person but fail to match when viewed by a another person. Observer metameric failure is the reason there were 31 individuals tested to derive the original 1931 "standard observer" values adopted by the ISO and that are still used today as the basis for the majority of color science.
Field-size metameric failure This occurs because the relative proportions of the three light sensitive cone types in the retina of the eye vary from the center of the visual field to the periphery. The result is that colors that match when viewed as very small, centrally fixated areas may appear different when presented as large color areas. This is the reason why color painted on a wall may appear different than the paint chip used to select the color even though they match when the chip is placed on the wall. In print production field-size metameric failure typically occurs when small PMS swatchbook samples are used to specify a PMS color that will cover a large press sheet area.
Geometric metameric failure Normally, material attributes such as translucency, gloss or surface texture are not considered in color matching. However here, identical colors appear different when viewed at different angles, distances, light positions, etc. Geometric metameric failure is most often seen when using metallic inks or paper, and specialty ink coatings or papers.
Tips for dealing with metameric failure
1. Be aware that it exists and may be the "simple" issue causing any color match issues.
2. If color needs to align across different lighting conditions choose pigments carefully or make the ink formulator aware of that requirement.
3. Control your lighting conditions - both for producing prints, final viewing (where possible), and for critical evaluation. The industry standard light source is referred to as "D50" or "D65" (5,000° Kelvin (North America), 6,500° (Europe).
4. Invest in PIA/GATF RHEM light indicators for everyone in the production chain that is involved in evaluating and approving color. RHEM light indicators are small (2" x 3/4") paper stickers with a unique printed design that uses metameric failure to indicate whether or not the viewing conditions are 5,000° K or not.
The stickers can be affixed to proofs or simply carried in a protective wrapper in purse or wallet.
5. Printshops should have viewing areas away from the press that allow print customers to view the presswork under typical lighting conditions (fluorescent and incandescent).
6. Be sure that all instruments (e.g. spectrophotomers) that are used for color evaluation are set to the same standard illuminant, D50 or D65, and same observer angle (typically 2°).
Tuesday, May 25, 2010
The Wayback View – Stereotype plate making
A trip to our local charity thrift shop this week turned up a surprising treasure:
This is a paper matrix that was used to cast the plate for the September 27, 1971 front page of our local newspaper. This close up shows how deep the original halftone image (on the left) and type (on the right) were pressed into the paper matrix that would later be covered in molten metal to form the actual printing plate:
Here is a short video clip from 1950 that shows the process of making a newspaper stereotype plate from a paper matrix.
Preview images from the video
Please press the play arrow to view the video. Note that it may stop for a moment while the video buffers in the background.
This is a paper matrix that was used to cast the plate for the September 27, 1971 front page of our local newspaper. This close up shows how deep the original halftone image (on the left) and type (on the right) were pressed into the paper matrix that would later be covered in molten metal to form the actual printing plate:
Here is a short video clip from 1950 that shows the process of making a newspaper stereotype plate from a paper matrix.
Please press the play arrow to view the video. Note that it may stop for a moment while the video buffers in the background.
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