Unless there are chargeable customer alterations, the maximum profit the printer will ever see on a specific job will be when their customer awards the project to them based on the quote. As soon as the printer begins the manufacturing process they also begin to erode that profit with inefficient workflows, duplication of effort, technical mistakes, errors in communication, etc.
Bottom line – profits are not what the printer is able to make, they are what the printer manages not to lose.
Saturday, January 31, 2009
Thursday, January 29, 2009
Printing at DMaxx - maximizing the CMYK gamut
The published standard solid ink density (SID) targets and their associated CIEL*a*b* values are designed to be be achievable by the majority of printshops with equipment in reasonable working order. They are great for standardizing presswork across the industry. However, they do not represent the best that can be achieved on press nor do they allow for competitive differentiation. Printing to "DMaxx" - the maximum, stable, SIDs the press is capable of while using standard process inks - provides a quick and relatively easy way to add visual impact to presswork, as well as a competitive edge, when appropriate, for specific print projects.
This process is best suited to sheetfed printers with an inline coater as this helps prevent setoff caused by the heavy ink densities. To prevent sheet distortion, use coated sheets in heavy text or cover basis weights. CMYK separations done with UCR rather than GCR work best with this process.
The basic recipe for DMaxx printing:
1) Benchmark your presswork.
You'll need about 2,000 sheets of paper and two hours press time. Create a target strip consisting of 12 tone patch steps – 1, 2, 5, 10, 25, 50, 75, 90, 95, 98, 99, and 100%, for each process color. Include four gray balance patches – typically, highlight (10C/7M/7Y), quarter-tone (25C/16M/16Y), mid-tone (50C/39M/39Y), and three-quarter-tone (75C/63M/63Y). These tone patches should be located near their nearest black tone equivalents (10K, 25K, 50K, 75K) to allow for visual comparison.
Include a standard CMYK image for visual evaluation.
Arrange the targets "in-line" on your press sheet and run to your standard house SIDs.
Mark the paper delivery stack "house standard" at the point the press is up to color and pull a few sheets for reference. Then gradually increase the ink densities. Try and go in 10 point steps. It is not unusual to be able to increase SIDs by 15-25 points and still maintain press stability. Don't worry about how the images and tone targets look at this point - just maintain gray balance.
Maximum SIDs are arbitrarily reached at the point where the press is still stable, ink/water balance is stable, dots are still sharp (no slinging or tailing), and set-off is not a threat. Mark the paper delivery at that point as "Max Ink" and pull several sheets for reference.
2) Chart a dot gain curve
Measure the target tone areas of your house standard sheet and plot them on a graph comparing requested tones vs actual press sheet values. Draw a "best fit" curve through the data points. This charts the dot gain characteristic curve of your press work at normal SIDs.
Now measure the tone values of the Max Ink sheet and plot them on a similar graph. Draw the best fit curve. This charts the dot gain characteristic curve of your press work at maximum SIDs.
This information will be used to create a dot gain compensation curve that will be applied to plate output to compensate for the increased dot gain caused by the boosted ink density.
3) Create the dot gain compensation curves
A dot gain compensation curve is derived from a plot of requested tone values against the resulting tone values. For example, if the house standard 50% requested tone resulted in a dot area of 67%, but The Max Ink measured 67% tone value corresponded to a 35% requested tone – then one of the points on your compensation curve would be: 50% = 35%. Put another way, we build a transfer curve that maps a requested tone of 50% to 35% because we know that 35% produces a 67% dot area at maximum ink density (which is what we are trying to achieve). This process would be applied to all the specified data points in order to align the tones of the High Ink presswork to the house standard.
4) Update your proofer
If you have a digital proofer you may want to build a profile of your DMaxx press work in order to properly set customer expectations in your proofs for this process. Alternatively you might stay with your current proofing and just tell customers that color will be boosted on press. This gives your press operators more leeway in how high they will run their SIDs.
This process is best suited to sheetfed printers with an inline coater as this helps prevent setoff caused by the heavy ink densities. To prevent sheet distortion, use coated sheets in heavy text or cover basis weights. CMYK separations done with UCR rather than GCR work best with this process.
The basic recipe for DMaxx printing:
1) Benchmark your presswork.
You'll need about 2,000 sheets of paper and two hours press time. Create a target strip consisting of 12 tone patch steps – 1, 2, 5, 10, 25, 50, 75, 90, 95, 98, 99, and 100%, for each process color. Include four gray balance patches – typically, highlight (10C/7M/7Y), quarter-tone (25C/16M/16Y), mid-tone (50C/39M/39Y), and three-quarter-tone (75C/63M/63Y). These tone patches should be located near their nearest black tone equivalents (10K, 25K, 50K, 75K) to allow for visual comparison.
Include a standard CMYK image for visual evaluation.
Arrange the targets "in-line" on your press sheet and run to your standard house SIDs.
Mark the paper delivery stack "house standard" at the point the press is up to color and pull a few sheets for reference. Then gradually increase the ink densities. Try and go in 10 point steps. It is not unusual to be able to increase SIDs by 15-25 points and still maintain press stability. Don't worry about how the images and tone targets look at this point - just maintain gray balance.
Maximum SIDs are arbitrarily reached at the point where the press is still stable, ink/water balance is stable, dots are still sharp (no slinging or tailing), and set-off is not a threat. Mark the paper delivery at that point as "Max Ink" and pull several sheets for reference.
2) Chart a dot gain curve
Measure the target tone areas of your house standard sheet and plot them on a graph comparing requested tones vs actual press sheet values. Draw a "best fit" curve through the data points. This charts the dot gain characteristic curve of your press work at normal SIDs.
Now measure the tone values of the Max Ink sheet and plot them on a similar graph. Draw the best fit curve. This charts the dot gain characteristic curve of your press work at maximum SIDs.
This information will be used to create a dot gain compensation curve that will be applied to plate output to compensate for the increased dot gain caused by the boosted ink density.
3) Create the dot gain compensation curves
A dot gain compensation curve is derived from a plot of requested tone values against the resulting tone values. For example, if the house standard 50% requested tone resulted in a dot area of 67%, but The Max Ink measured 67% tone value corresponded to a 35% requested tone – then one of the points on your compensation curve would be: 50% = 35%. Put another way, we build a transfer curve that maps a requested tone of 50% to 35% because we know that 35% produces a 67% dot area at maximum ink density (which is what we are trying to achieve). This process would be applied to all the specified data points in order to align the tones of the High Ink presswork to the house standard.
4) Update your proofer
If you have a digital proofer you may want to build a profile of your DMaxx press work in order to properly set customer expectations in your proofs for this process. Alternatively you might stay with your current proofing and just tell customers that color will be boosted on press. This gives your press operators more leeway in how high they will run their SIDs.
Tuesday, January 27, 2009
Outfacing and infacing investments
It's a principle that may seem obvious, but it is one that's often forgotten when a printshop is investigating a new investment opportunity.
There are two key issues that every printshop must resolve in their day-to-day activities in order to maximize their potential for success. First is that they must meet customer expectations, because if they fail to do that, customers will go elsewhere for their work. Second is that they must meet production requirements for a cost efficient, effective, print manufacturing process otherwise they will lose profitability and very quickly be out of business. Therefore, any prospective investment in technology, business systems, or production methods should be evaluated in the light of the outfacing, or positive customer impact, as well as the infacing, or positive internal production impact. A single investment that positively impact either area is good. However, single investments that positively impact both areas are best.
There are two key issues that every printshop must resolve in their day-to-day activities in order to maximize their potential for success. First is that they must meet customer expectations, because if they fail to do that, customers will go elsewhere for their work. Second is that they must meet production requirements for a cost efficient, effective, print manufacturing process otherwise they will lose profitability and very quickly be out of business. Therefore, any prospective investment in technology, business systems, or production methods should be evaluated in the light of the outfacing, or positive customer impact, as well as the infacing, or positive internal production impact. A single investment that positively impact either area is good. However, single investments that positively impact both areas are best.
Sunday, January 25, 2009
The Rule of 10x
Saturday, January 24, 2009
Aligning proof and presswork
The process of aligning proof and presswork generally follows the basic steps outlined below. This procedure applies primarily to Strategy One as outlined in my January 18, 2009 blog posting. However, it can certainly be modified to for Strategies Two and Three.
01) Identify the target for your presswork. This can be an internal standard or industry specification (e.g. ISO, GRACoL7, SWOP, etc.)
02) Get consensus and buy-in from the stakeholders (prepress, pressroom, management). Change is always disruptive, however, if everyone affected is on board you will have a much better chance at success.
03) Determine who's going to be the lead implementer (i.e. internal resource or outside consultant will be used). Be honest in your evaluation of internal competence. Recognize that if you do it yourself, even if you fail, you will get a greater understanding of the process and therefore be in a better position to evaluate an outside resource should that end up being needed.
04) Open a docket. The process will consume company resources which need to be accounted for. Also the project will need to be treated seriously and given the proper time and involvement. Dockets help to ensure that happens.
05) Contact your ink vendor to determine if your current inks can achieve your target. If not, identify with your supplier, an ink series that has proven capable.
06) Contact your proof/workflow vendor to determine how to set up your proofer to output proofs that align to the industry specification you have decided on.
07) Find a paper for your press that aligns to the brightness defined in the specification. Try to find one that has a similar UV optical brightner content to your proofing media. You can use a $10 black light to do a qualitative comparison. Make sure the bulb is fluorescent not incandescent. Proof and press paper should glow, or not glow, by about the same amount. If there is a big difference with your press/proofer paper in terms of optical brightners used you will have problems.
08) Confirm that instruments used in prepress and pressroom are in proper working condition, calibrated, set to the same standard, and agree with one another.
09) Confirm that your CtP device imaging is consistent, across the plate and plate to plate. Consistency is more important than accuracy.
10) Test the press. This involves running a test form, preferably without images or proof, to determine the mechanical/chemical soundness of the press. If the press not stable that will need to be addressed first.
11) Assuming that #10 was a success (with your inks and papers) and that you were able to hit the required CIEL*a*b* values at the appropriate solid ink densities - then build plate curves to align the tone response of your presswork to your proof.
12) Go on press to confirm alignment between proof and press sheet. For this test form you can add subjective reference images to your objective measurable targets.
13) Assuming that #12 was a success. Catalog and document plates, proofs, and presswork. This will become your "golden reference." If anything goes wrong in future production, you would run this golden reference to determine what has changed.
14) You may, optionally, characterize your presswork and use the resulting profile to fine tune your proof to your press that is now conforming to the industry specification.
01) Identify the target for your presswork. This can be an internal standard or industry specification (e.g. ISO, GRACoL7, SWOP, etc.)
02) Get consensus and buy-in from the stakeholders (prepress, pressroom, management). Change is always disruptive, however, if everyone affected is on board you will have a much better chance at success.
03) Determine who's going to be the lead implementer (i.e. internal resource or outside consultant will be used). Be honest in your evaluation of internal competence. Recognize that if you do it yourself, even if you fail, you will get a greater understanding of the process and therefore be in a better position to evaluate an outside resource should that end up being needed.
04) Open a docket. The process will consume company resources which need to be accounted for. Also the project will need to be treated seriously and given the proper time and involvement. Dockets help to ensure that happens.
05) Contact your ink vendor to determine if your current inks can achieve your target. If not, identify with your supplier, an ink series that has proven capable.
06) Contact your proof/workflow vendor to determine how to set up your proofer to output proofs that align to the industry specification you have decided on.
07) Find a paper for your press that aligns to the brightness defined in the specification. Try to find one that has a similar UV optical brightner content to your proofing media. You can use a $10 black light to do a qualitative comparison. Make sure the bulb is fluorescent not incandescent. Proof and press paper should glow, or not glow, by about the same amount. If there is a big difference with your press/proofer paper in terms of optical brightners used you will have problems.
08) Confirm that instruments used in prepress and pressroom are in proper working condition, calibrated, set to the same standard, and agree with one another.
09) Confirm that your CtP device imaging is consistent, across the plate and plate to plate. Consistency is more important than accuracy.
10) Test the press. This involves running a test form, preferably without images or proof, to determine the mechanical/chemical soundness of the press. If the press not stable that will need to be addressed first.
11) Assuming that #10 was a success (with your inks and papers) and that you were able to hit the required CIEL*a*b* values at the appropriate solid ink densities - then build plate curves to align the tone response of your presswork to your proof.
12) Go on press to confirm alignment between proof and press sheet. For this test form you can add subjective reference images to your objective measurable targets.
13) Assuming that #12 was a success. Catalog and document plates, proofs, and presswork. This will become your "golden reference." If anything goes wrong in future production, you would run this golden reference to determine what has changed.
14) You may, optionally, characterize your presswork and use the resulting profile to fine tune your proof to your press that is now conforming to the industry specification.
Monday, January 19, 2009
The Printing of Barack Obama's official portrait
In preparation for the January 21, 2009 inauguration of Barack Obama, the U.S Government Printing Office (GPO) produces the official portrait of the President.At the press check
The GPO provides publishing & dissemination services for the official & authentic government publications to Congress, Federal agencies, Federal depository libraries, & the American public.
Please press the play arrow to view the video. Note that it may stop for a moment while the video buffers in the background.
The GPO provides publishing & dissemination services for the official & authentic government publications to Congress, Federal agencies, Federal depository libraries, & the American public.
Please press the play arrow to view the video. Note that it may stop for a moment while the video buffers in the background.
Sunday, January 18, 2009
Press and proof alignment strategies
Strategies for answering the critical question: should your press color align to your proof or should the proof color align to the press?
• Strategy One: Targeting an Industry Defined Specification - the press aligns to the proof
If you do not control 100% of the digital files entering your pressroom it would be best to target an industry-defined specification as a way of bringing some degree of order to the various inputs that you receive. This strategy also allows prepress tradeshops and production graphic designers to prepare image scans and digital artwork appropriately even when they don't know which printer will be doing the final presswork.
This strategy is most appropriate in a distributed printing environment where prepress and scans from a variety of sources must conform to a common print characteristic. Examples are magazine and newspaper advertising or brochures that will be printed at a variety of locations.
Aligning the press to the proof is embodied in the traditional, analog film-based, laminate proofing systems with the most popular implementation for offset printing being SWOP. It is also the process embodied in the GRACoL 7/G7 specification.
• Strategy Two: Proofing to a Shop-Specific Presswork Target - the proof aligns to the press
With this strategy, the presswork color is the target and the proof is aligned to it. This strategy is appropriate in a non-distributed printing environment where prepress and scans are completely controlled by the printer or where the printer has a close relationship with the print specifier. Examples include brochures, collateral materials, annual reports, corporate brochures, art reproduction, and so on. This strategy is often used by printers wishing to differentiate their presswork from their competition. In this case print purchasers are primarily concerned that their particular project looks as good as possible in print. The presswork is unique — either to the individual print shop or even to a specific press in the shop.
• Strategy Three: - Align to Your Customer
Just as one size does not fit all - one print characteristic may not suit all. In today's highly competitive print environment, it can make competitive sense for the printer to leverage the flexibility of digital proofing and plating systems to offer multiple print characteristics to their customers. I.e. both strategy One and Two could be offered as options.
This initially involves greater complexity in workflow, however, once set up can provide the printer with tremendous flexibility in differentiating themselves and better meeting their customer's requirements in print.
Saturday, January 17, 2009
Some things I learned from engineers (that printshop folks might find useful)
Yes, this photo of an engineer is a bit harsh, but not as harsh as the culture shock I had moving from a prepress/printshop to Creo in 1997. Although I had worked with engineers before - as a graphic designer promoting their wares (telecommunications systems, side-looking airborne radar imaging systems, and paper mill optimizing systems) the experience did not really prepare me for working with them in the development and marketing of graphic arts systems - a subject much closer to my heart. Their attitude towards printers was that if the printer got it right it was due to their skills in art of printing. But if they knew why they got it right - that was the science of printing. So, one of my main responsibilities at Creo was to bridge the art and science of printing on behalf of its customers and prospects as a way to make them and Creo more successful.
Here are some things that I learned from working with those engineers that printshop folks might find useful.
1) Record it. Engineers invariably make notes in their daybooks during meetings or whenever they have an idea. They don't trust memory. However mundane the discussion, they record it. If only printshop employees were as diligent in making notes of discoveries, errors, tricks, etc.. They might avoid making the same mistake twice. The knowledge gained by one could be shared and benefit all.
2) Processes can be "deterministic." There is no voodoo or black art. One makes a certain input, therefore one can expect a certain output. If the output is not what one expected - it is not "sunspots" that are the problem. One can figure out what caused the problem if one applies:
3) Basic High School Science. The reason we were forced to take science in high school was to understand the scientific method because our teachers knew that we could use it in our lives to help answer questions that had not yet been thought of. Basically it is a way to objectively ask and resolve unknowns by making observations and doing experiments. The steps of the scientific method are to:
a) Ask a question
b) Do background research
c) Construct a hypothesis
d) Test the hypothesis by doing an experiment. It is important the experiment to be a fair test which occurs when only one factor (variable) changes and that "apples" are indeed compared to "apples"
e) Analyze the data and draw a conclusion
f) Communicate the results
4) Use the right words correctly. If you hear a press operator say "blue" when they mean "cyan" you have a problem. Most screw-ups, misunderstandings, and difficulties in solving problems result from sloppy and/or inappropriate word usage.
5) Read what is written. Do not read into what is written.
6) Hear what is said. Do not read into what is said.
7) If you don't know or understand something that's OK. Say so and get clarification.
8) If you don't know the answer don't offer one.
9) Just because it is "common knowledge" or "obvious" or what "everyone says" or what some "authority states" does not make it so.
10) Think. Take the time. Chart out the issue. Drill down to the core problem. Don't assume.
Here are some things that I learned from working with those engineers that printshop folks might find useful.
1) Record it. Engineers invariably make notes in their daybooks during meetings or whenever they have an idea. They don't trust memory. However mundane the discussion, they record it. If only printshop employees were as diligent in making notes of discoveries, errors, tricks, etc.. They might avoid making the same mistake twice. The knowledge gained by one could be shared and benefit all.
2) Processes can be "deterministic." There is no voodoo or black art. One makes a certain input, therefore one can expect a certain output. If the output is not what one expected - it is not "sunspots" that are the problem. One can figure out what caused the problem if one applies:
3) Basic High School Science. The reason we were forced to take science in high school was to understand the scientific method because our teachers knew that we could use it in our lives to help answer questions that had not yet been thought of. Basically it is a way to objectively ask and resolve unknowns by making observations and doing experiments. The steps of the scientific method are to:
a) Ask a question
b) Do background research
c) Construct a hypothesis
d) Test the hypothesis by doing an experiment. It is important the experiment to be a fair test which occurs when only one factor (variable) changes and that "apples" are indeed compared to "apples"
e) Analyze the data and draw a conclusion
f) Communicate the results
4) Use the right words correctly. If you hear a press operator say "blue" when they mean "cyan" you have a problem. Most screw-ups, misunderstandings, and difficulties in solving problems result from sloppy and/or inappropriate word usage.
5) Read what is written. Do not read into what is written.
6) Hear what is said. Do not read into what is said.
7) If you don't know or understand something that's OK. Say so and get clarification.
8) If you don't know the answer don't offer one.
9) Just because it is "common knowledge" or "obvious" or what "everyone says" or what some "authority states" does not make it so.
10) Think. Take the time. Chart out the issue. Drill down to the core problem. Don't assume.
Friday, January 16, 2009
Halftones and grey levels explained
Some principles of halftones and the myth of grey level capability.
This information is basically true for all vendor's offerings.
A halftone dot is formed inside a halftone "cell" The cell is a grid of pixels which are turned on to form the dot. The cell begins with no pixels turned on (0% tone) and as pixels are turned on the dot grows until all the pixels within the cell are turned on and the cell is filled (i.e. 100% tone).For example.
If the cell size is 2 pixels wide by 2 pixels deep the halftone cell will contain a total of 4 pixels. As a result the following halftone dot tone values can be created:
0% = all pixels off
25% = 1 pixel turned on
50% = 2 pixels turned on
75% = 3 pixels turned on
100% = 4 pixels turned on.
So, with a 2x2 pixel halftone cell it is only possible to have 5 tone levels (grey levels). I.e. the total number of tones possible equals the total number pixels available plus one. In this case 2x2=4 4+1 = 5.
If the number of pixels is increased within the cell by making them smaller - i.e. cell size remains the same but the pixels are smaller - then the number of possible grey levels goes up.
For example:
For a 3x3 cell the number of possible grey levels is 10 (3x3=9, 9+1=10
For a 10x10 cell the number of possible grey levels is 101 (10x10=100, 100+1=101
For a 16x16 cell the number of possible grey levels is 257 (16x16=256, 257+1=257)
In a basic AM screen the dot is formed by turning on pixels starting from the center of the cell. For a basic FM screen the pixels within the cell are turned on pseudo-randomly.
So, as resolution (the "dpi" of the recording device) increases - grey levels increases. As resolution decreases grey levels decrease.
If the resolution (dpi) is fixed but the number of adjacent cells is increased (lpi, i.e. going from 100 lpi to 175 lpi) then the number of pixels available for each dot decreases and therefore the number of grey levels decreases.
This principle is captured by the classic formula:
(dpi/lpi) squared + 1 = number of grey levels
So for a 2400 dpi output device:
At 100 lpi:
2400 dpi/100 lpi = 24 squared = 576 plus one = 577 tones possible. No problem - more than enough grey levels.
But at 175 lpi:
2400 dpi/175 lpi = 13.7 squared = 188 plus one = only 189 tones possible. A big problem because when the ratio of dpi to lpi drops below 16, the number of available grey levels drops to below 256. This can result in tonal reproduction that is inaccurate and uneven, causing visible shadestepping (a.k.a. banding or contouring) in gradients. Color steps abruptly from one tone to the next without a smooth transition.
In 1984 the screening technology described in part one was the state of art for halftone screening with Postscript devices.
The only way to recoup the lack of tones as one went to higher lpis was to increase the device dpi. I.e. go from 2400 dpi to 3200 dpi or higher. The penalty was slower imaging times and increased process control required in the film workflows of the day.
However, the formula is only true for the tone represented by a single, isolated, halftone dot based on an individual halftone dot cell - something that never occurs in real production environments. So, around 1989 a new approach began to be adopted. The approach is based on the fact that we don't care about individual halftone dots. What is important is the tone represented in an area. For example, let's say that we want to see a 17% tone patch value in the presswork. However, if we cannot represent that area with individual 17% dots – because of that classic formula limitation – we can still create the 17% value by alternating 16% dots and 18% dots (this is called "dithering"). The eye (and instruments) integrate the alternating 16% and 18% dots and the result is the average value - in this example 17% – our desired tone value.
Another way to look at it is: if we constrain our halftone cell to a pixel matrix of 16 x 16 pixels then we will always have 257 levels of grey in an area irrespective of how the dots within the cell are organized. However, if we build a tone area based on multiple halftone cells – a "supercell" we can get around the grey level limitations the formula would suggest.
As one example, the highest lpi on a 2400 dpi device that I'm aware of was 1697 lpi on a poster printed with plates imaged on a Creo CtP device in 2000 by Metropolitan Fine Printers in Vancouver Canada. It won a "They said it can't be done" award at GrapExpo in Chicago.
Supercell screening gets around the grey level limitations of the classic formula by looking at a tone area (the important criteria) rather than an individual dot. As a result, since about 1995 all AM screens from all vendors adopted variants of supercell screening technology:
Agfa - ABS - Agfa Balanced Screening
Heidelberg - HDS - High Definition Screening, and later IS screening
Harlequin - HPS - Harlequin Precision Screening
Creo/Kodak - Creosettes/Maxtone
Fuji - just since 2004 CoRes screening
etc.
As a result, 2400 dpi has become the defacto standard for imaging resolution in the commercial print industry. Higher resolutions, as far as halftone screening and grey levels is concerned, provides no additional value while imposing a penalty on imaging time.
Where the various vendors distinguish themselves with their individual implementation of supercell screening is how they deal with issues such as rosette drift - the gradual shift from clear centered rosette to dot centered rosette - over the width of the plate, single channel moiré, miniscus effects as dots first touch, e.g. at the 50% point, and other nuances of halftone screening.
Once you've passed the 200 lpi frequency - the human eye can no longer resolve the halftone structure at normal viewing distances. Beyond 200 lpi the argument can be made that there is no need to be constrained to the AM halftone structure. You might as well use an FM type screen. The lithographic issues will be the same since the imaging and press issues result from the size of halftone dots - not how they are organized.
This information is basically true for all vendor's offerings.
A halftone dot is formed inside a halftone "cell" The cell is a grid of pixels which are turned on to form the dot. The cell begins with no pixels turned on (0% tone) and as pixels are turned on the dot grows until all the pixels within the cell are turned on and the cell is filled (i.e. 100% tone).For example.
If the cell size is 2 pixels wide by 2 pixels deep the halftone cell will contain a total of 4 pixels. As a result the following halftone dot tone values can be created:
0% = all pixels off
25% = 1 pixel turned on
50% = 2 pixels turned on
75% = 3 pixels turned on
100% = 4 pixels turned on.
So, with a 2x2 pixel halftone cell it is only possible to have 5 tone levels (grey levels). I.e. the total number of tones possible equals the total number pixels available plus one. In this case 2x2=4 4+1 = 5.
If the number of pixels is increased within the cell by making them smaller - i.e. cell size remains the same but the pixels are smaller - then the number of possible grey levels goes up.
For example:
For a 3x3 cell the number of possible grey levels is 10 (3x3=9, 9+1=10
For a 10x10 cell the number of possible grey levels is 101 (10x10=100, 100+1=101
For a 16x16 cell the number of possible grey levels is 257 (16x16=256, 257+1=257)
In a basic AM screen the dot is formed by turning on pixels starting from the center of the cell. For a basic FM screen the pixels within the cell are turned on pseudo-randomly.
So, as resolution (the "dpi" of the recording device) increases - grey levels increases. As resolution decreases grey levels decrease.
If the resolution (dpi) is fixed but the number of adjacent cells is increased (lpi, i.e. going from 100 lpi to 175 lpi) then the number of pixels available for each dot decreases and therefore the number of grey levels decreases.
This principle is captured by the classic formula:
(dpi/lpi) squared + 1 = number of grey levels
So for a 2400 dpi output device:
At 100 lpi:
2400 dpi/100 lpi = 24 squared = 576 plus one = 577 tones possible. No problem - more than enough grey levels.
But at 175 lpi:
2400 dpi/175 lpi = 13.7 squared = 188 plus one = only 189 tones possible. A big problem because when the ratio of dpi to lpi drops below 16, the number of available grey levels drops to below 256. This can result in tonal reproduction that is inaccurate and uneven, causing visible shadestepping (a.k.a. banding or contouring) in gradients. Color steps abruptly from one tone to the next without a smooth transition.
In 1984 the screening technology described in part one was the state of art for halftone screening with Postscript devices.
The only way to recoup the lack of tones as one went to higher lpis was to increase the device dpi. I.e. go from 2400 dpi to 3200 dpi or higher. The penalty was slower imaging times and increased process control required in the film workflows of the day.
However, the formula is only true for the tone represented by a single, isolated, halftone dot based on an individual halftone dot cell - something that never occurs in real production environments. So, around 1989 a new approach began to be adopted. The approach is based on the fact that we don't care about individual halftone dots. What is important is the tone represented in an area. For example, let's say that we want to see a 17% tone patch value in the presswork. However, if we cannot represent that area with individual 17% dots – because of that classic formula limitation – we can still create the 17% value by alternating 16% dots and 18% dots (this is called "dithering"). The eye (and instruments) integrate the alternating 16% and 18% dots and the result is the average value - in this example 17% – our desired tone value.
Another way to look at it is: if we constrain our halftone cell to a pixel matrix of 16 x 16 pixels then we will always have 257 levels of grey in an area irrespective of how the dots within the cell are organized. However, if we build a tone area based on multiple halftone cells – a "supercell" we can get around the grey level limitations the formula would suggest.
As one example, the highest lpi on a 2400 dpi device that I'm aware of was 1697 lpi on a poster printed with plates imaged on a Creo CtP device in 2000 by Metropolitan Fine Printers in Vancouver Canada. It won a "They said it can't be done" award at GrapExpo in Chicago.
Supercell screening gets around the grey level limitations of the classic formula by looking at a tone area (the important criteria) rather than an individual dot. As a result, since about 1995 all AM screens from all vendors adopted variants of supercell screening technology:
Agfa - ABS - Agfa Balanced Screening
Heidelberg - HDS - High Definition Screening, and later IS screening
Harlequin - HPS - Harlequin Precision Screening
Creo/Kodak - Creosettes/Maxtone
Fuji - just since 2004 CoRes screening
etc.
As a result, 2400 dpi has become the defacto standard for imaging resolution in the commercial print industry. Higher resolutions, as far as halftone screening and grey levels is concerned, provides no additional value while imposing a penalty on imaging time.
Where the various vendors distinguish themselves with their individual implementation of supercell screening is how they deal with issues such as rosette drift - the gradual shift from clear centered rosette to dot centered rosette - over the width of the plate, single channel moiré, miniscus effects as dots first touch, e.g. at the 50% point, and other nuances of halftone screening.
Once you've passed the 200 lpi frequency - the human eye can no longer resolve the halftone structure at normal viewing distances. Beyond 200 lpi the argument can be made that there is no need to be constrained to the AM halftone structure. You might as well use an FM type screen. The lithographic issues will be the same since the imaging and press issues result from the size of halftone dots - not how they are organized.
Thursday, January 15, 2009
Quality printing defined
Pronunciation: kwä-li-tE
1: a distinguishing attribute
2: an inherent feature
3: a peculiar and essential character
• Merriam-Webster DictionaryAsk a room full of printers whether they would define themselves as "quality" printers and, after a moment of confusion, they would as a rule agree that indeed, yes, they would define themselves as “quality” printers. However, ask them to describe in concrete terms what that means and they typically respond with a blank stare. Well, dictionaries define “quality” as a “distinguishing attribute” or “inherent feature.” So, one might say that a quality printer is simply one that has the attribute of being distinct. Or putting it another way, given that quality is concerned with meeting customer expectations, quality printers distinguish themselves by meeting customer – rather than supplier (i.e. printer) – expectations.
1: a distinguishing attribute
2: an inherent feature
3: a peculiar and essential character
• Merriam-Webster DictionaryAsk a room full of printers whether they would define themselves as "quality" printers and, after a moment of confusion, they would as a rule agree that indeed, yes, they would define themselves as “quality” printers. However, ask them to describe in concrete terms what that means and they typically respond with a blank stare. Well, dictionaries define “quality” as a “distinguishing attribute” or “inherent feature.” So, one might say that a quality printer is simply one that has the attribute of being distinct. Or putting it another way, given that quality is concerned with meeting customer expectations, quality printers distinguish themselves by meeting customer – rather than supplier (i.e. printer) – expectations.
Wednesday, January 14, 2009
You are who you compete against.
Who your customers have you compete against not only tells you a great deal about how you are perceived by that individual print buyer, but by other prospective customers as well. What shared characteristics do you think caused the print buyer to group you with those specific printers? Was it equipment, services, capabilities? Are you competing against the printers you would have chosen had you been the print buyer? If not, why not? Finally, and most importantly, if you think the companies that print buyers associate you with to compete against are inappropriate, what are you actually going to do to correct the perception?
Wednesday, January 7, 2009
‘Custom’ is six-eighths of ‘customer.’
Presswork expectations are different from print buyer to print buyer. The presswork that one customer may require might be rejected outright by another – like the limited edition artist pictured above. Also, each print buyer will have different priorities and expectations from one project to another. Today pleasing color for a flyer. Tomorrow hi-fidelity for an Annual Report. One size – or presswork standard – does not fit all. However, if you tailor your production workflow and presswork look to meet the individual customer’s requirements for the specific job at hand, you are no longer simply providing a commodity but rather becoming a valued partner – and you are also differentiating yourself. While you may not be able to charge any extra, your customer-centric capabilities may make the difference between your getting the project vs your competition.
Tuesday, January 6, 2009
High-end/Low-end
For the successful printer there is no “low-” or “high-end” – there is only one end: meeting customer expectations. They understand that if those expectations are not met, the print buyer will go elsewhere and eventually the printshop will go out of business.
It’s not about the printer’s priorities for the job. It’s not about how the printer perceives themselves. And it’s not solely about meeting a presswork specification. Rather, it’s about understanding and delivering on the specific print buyer’s success factors – their priorities. Shoes made with the finest materials, crafted with the best skills, have no value if they don’t fit the customer’s feet. Customers, and their individual projects, are all different – therefore the quality printer must have the flexibility to tune their production process, and its output, to fit their clients’ needs.
It’s not about the printer’s priorities for the job. It’s not about how the printer perceives themselves. And it’s not solely about meeting a presswork specification. Rather, it’s about understanding and delivering on the specific print buyer’s success factors – their priorities. Shoes made with the finest materials, crafted with the best skills, have no value if they don’t fit the customer’s feet. Customers, and their individual projects, are all different – therefore the quality printer must have the flexibility to tune their production process, and its output, to fit their clients’ needs.
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