Tuesday, March 17, 2009
Saturday, March 7, 2009
The issues of Optical Brightening Agents in paper and ink
As ICC color managed workflows become more prevalent in the graphic arts, so do the difficulties caused by OBAs (Optical Brightening Agents) that are encountered in the pressroom, prepress, and their customers. OBAs are used to increase the apparent brightness and whiteness of papers and their use is becoming more prevalent in paper manufacturing. They increase brightness and whiteness by absorbing energy in the ultra violet and emitting (fluoresce) the energy in the blue area of the visible spectrum. Because, to the eye, blue/white looks "whiter" than yellow/white OBAs are not really whiteners, but bluing agents. OBAs are also used in ink to expand gamut or brighten 4/C image printed on poor substrates - e.g. newsprint.When fluorescence is present, the light coming from the sample is the combination of the light that is reflected and the light that is fluoresced. ISO 12647-2 printing paper grades specifies low OBA content, however, there is no specification as to the amount of OBA content. And, although they typically use light sources with little or no UV radiance, there is no specification describing the UV content of light sources in measurement instruments such as spectrophotometers. The addition of fluorescence to either the inks or the substrate greatly increases the level of uncertainty in instrument readings of the optical properties of printed images. This, in turn, may lead to a significant lack of reproducibility between two imaging centers that attempt to apply color management principles to their individual measurements of the same image printed on various substrates.
While it is not practical for printers to quantitively measure the OBA content of the materials that they use, it is quite an easy matter to qualitatively see the OBA content. All it takes is an inexpensive (less than $15 USD) "black light" such as the one illustrated below (do not bother with incandescent black lights):
For example, with the black light it is easy to see that the paper used for the Pantone Goe system swatch book (on the left in the image below) contains more OBAs than the conventional Pantone spot color swatchbook on the right. Also, it's clear that the uncoated paper section in the Pantone spot color swatchbook contains more OBAs than the coated section.
The bottom line – the significance of which will be more apparent in the next parts of the blog on this topic – is that, although you may not be able to do anything about it, just being able to be aware of OBA content can help solve issues related to their use.OBAs are sometimes use as additives in ink. In the example below it has been used in the yellow ink in a process set – while the paper itself contains little if any OBAs.
Using OBAs in the yellow ink is a common strategy with newspaper printers as a way to add brightness to imagery and compensate for the poor whiteness of newspaper stock. The fact that the OBAs fade and cause a color shift over time is typically not a concern in that market. It is important to be aware of the OBA content of your process ink set particularly if the print specifier is concerned with the longevity of their printed materials - especially if they will be exposed to sunlight.OBAs are also used in so called Hi-Fi inks, notably those used in the Pantone Hexachrome process, to add vibrancy and expand the gamut beyond conventional four color process. However the OBAs can make the inks more problematic in the pressroom as well as result in presswork that does not have a long shelf life (due to fading and color shift).
The inks that are typically used in four color process printing block, to varying degrees, the fluorescence in papers containing OBAs. Black and magenta block the greatest amount, yellow a lesser amount, and cyan ink least of all. What this means is that when an image is printed using a halftone screen, lighter/pastel tones allow more more of the brightening and color shift of OBAs (towards blue) than the shadows. Color is effectively skewed towards the blue from shadows to highlights – but only when the paper being printed on has a high OBA content.
In daily presswork this disconnect usually appears in midtones and pastels – sometimes the color matches the proof in those areas and at other times the color doesn't – depending on the OBA content of the paper being run. FM screenining will lessen this effect. The effect on an AM screen is emphasized in the image below to illustrate the issue.
The use of OBAs in paper has a significant impact on the reliability of proofing and alignment of presswork to the proof. This is an issue where the use of a black light really "shines". When the proofing paper contains OBAs the hue of pastel colors can shift depending on the amount of UV being emitted by the viewing light source as illustrated below:
Although they cannot control the light under which their customers evaluate proofs, many printshops will use UV blocking filters to cover the D50 bulbs in their viewing booths. The notion is that, most of the time, the proof will be looked at by the customer under lighting with little UV content. The UV block filter helps the press operator to "ignore" the presence of OBAs in the proof/presswork.Another strategy is for the printshop to try and align the OBA content of their proofing paper and press sheets. A black light can provide a qualitative measure of the OBA content of the media as illustrated here using a vendor's swatchbook of their proofing media:
Selecting pairs of press and proofing papers according to their OBA content helps in the alignment of presswork and proofs and thereby enhances the printer's ability to set expectations correctly with their customers.
Tuesday, March 3, 2009
The Wayback View – The birth of a Mad Man - 1957
The birth of an advertising man is revealed in this poignant 1.34 second video as "Ted" goes to the big city in order to move up the ladder as a professional in the American social class system.
Monday, March 2, 2009
Print as Manufacturing?
From the print customer’s perspective, buying print is unlike any other buying experience. Imagine if cars were manufactured and purchased the way print is.The buyer would describe in general terms what sort of car they would like to have and make a request for a car manufacturing quote from a variety of car makers who may not be equally qualified to build it. The buyer then makes the purchase decision, perhaps based on price – "not too high, not too low" or perhaps based on a relationship with the car manufacturer's sales rep. Once the the selection of manufacturer is made, most of the raw materials and specifications needed to build the car are provided by the customer who, typically, has only a vague idea about how cars are built. The car manufacturer purchases a few required materials – however, they are provided with no specifications as to their manufacturing suitability. Then a car is mocked up as "proof" of concept using materials that only partially resemble the materials that will be used to build the final car. Then, after customer approval of the proof, the car buyer may opt to watch their car being manufactured so that they can make adjustments to the look of the car while it's being built.
Now, that’s manufacturing!
Friday, February 27, 2009
The Wayback View – Remote image transfer - 1944
Today's journalist brings a great deal of high technology to bear in getting the story out to the newswires. Digital photography allows images to be sent wirelessly via cellphone or computer uplink to satellites and then on to the news agencies for distribution. Surprisingly, in 1944 the process for a reporter at the Minnesota Star Journal and Tribune was not so different as this 2 minute long video shows.
Thursday, February 26, 2009
FM Screening Halftone Dot Shapes/Patterns
The choice of FM halftone dot shape is important because it has an impact on plate choice, plate imaging, the aesthetics of the final presswork as well as on the lithographic performance of the press. Because there can be a wider variation of FM dot shapes than AM, this post will just illustrate several representative dot shape options. Each vendors' offerings can then be evaluated by using the information in this post as a guide.In an FM screen each dot is formed in a halftone cell, typically based on a grid of 16 by 16 pixels. The pixels within the cell are "turned on" in pseudo random fashion in order to form the FM dot shape or tone area. The cells are then stitched together, like a mosaic, in order to form an area of dots or tone area.
On the left (enlarged) is a single halftone 16x16 pixel cell with several pixels turned on. On the right (reduced) is a tone area defined by a mosaic of sixteen individual 16x16 halftone cells.
Following are some basic FM screening dot shapes/patterns and their performance characteristics in use.
Click on the images to enlarge.
First Order FM: Dots are all the same size
Benefits:Image has a photographic quality even when viewed under a loupe. Often used for fine art reproductions.Issues:Grainy as well as mottled looking flat tone areas, small dots are more difficult to image consistently on plate and hold on press. Because the issues usually outweigh the benefits, this FM dot pattern is seldom used today except for specialized work.
Second Order FM (a.k.a. Hybrid FM): Dots grow in the tone scale
Second order FM screens are the de facto standard in today's print production. With this type of halftone screen the dots grow in size through the tone scale. Dot growth can be in one direction – perhaps forming worm-like features as in the first example (Kodak Staccato), or grow in both directions – forming more conventional looking dots as in the second example (Screen Spekta).Benefits:Depending on the specific vendor's implementation, graininess in flat tone areas is eliminated.
Issues:Thin one or two pixel wide worm features, as in the first example, may demand higher resolution plates, and/or imaging in order to maintain consistency. Dots shapes, as in the second example, may cause a propensity for shadows to plug on press.
Second Order directional FM: Dots grow directionally in the tone scale
Dots have a strong directionality. Sometimes this dot shape in a vendor's FM offering is used for only one of the process colors in order to reduce "clumping" or secondary patterns when process colors overprint.Benefits:Eliminates secondary patterns when process colors overprint.
Issues:Directionality of the dot shape can exaggerate directional issues, such as slur and doubling, on press.
Nasty FM: Dots are plain ugly
This graphic is just intended to emphasize the fact that there is a great variety in FM screen patterns. Therefore one should not apply general statements such as "FM screening is grainy" – quality will vary according to each vendor's implementation.
Monday, February 23, 2009
AM Screening Halftone Dot Shapes
The choice of halftone dot shape is important because it has an impact on the aesthetics of the final presswork as well as on the lithographic performance of the press. This post describes the basic dot shape options available with conventional "AM" halftone screening. The descriptions apply to all the various vendors' offerings – though there will be some very subtle variations between their various implementations.When dots grow in size from highlight to shadow there is a point at which the dots first touch each other. When that happens there is an effect called the “optical bump.” In a gradient blend this may show up as an artifact of a dark line in an otherwise smooth blend. Another issue is that, because paper moves through a press from printing unit to printing unit, presses are effectively directional imaging devices. This means that halftone dots shapes that are also directional, can interact with the directionality of the press and may exaggerate some issues such as slur and doubling.
In an AM screen each dot is formed in a halftone cell, typically based on a grid of 16 by 16 pixels. The pixels within the cell are "turned on" in order to form the dot shape. The cells are then stitched together, like a mosaic, in order to form an area of dots.
On the left (enlarged) is a single halftone dot within its 16x16 pixel cell. On the right (reduced) is an area of dots within their 16x16 pixel cells.
Following are the basic AM screening dot shapes and their performance characteristics in use.
Click on the images to enlarge.
Round dot: Dots are round through the tone range
Benefits: Dot shape is the same for all screen angles and frequencies, optical bump is hidden in the shadows at the 75% tone, dot is non-directional so it is less affected by press problems. Reduces single channel moiré issues. Dot is non directional, i.e. all screen angle dots react the same to directional press issues such as slur and doublingIssues: Not suited for film-imaged plates because the diamond shape that results at 75% and darker tones is very sensitive to dot gain and sudden loss of shadow detail. Excellent for computer-to-plate imaging because of the greater integrity of halftone imaging as well as the ease of dot gain compensation with tone reproduction curves.
Euclidean dot (a.k.a. Transforming Round Dot): Round/Square/Round
This is the classic dot shape that resulted from the original etched glass screens from the 19th century and is now replicated in digital form.Benefits: Dot shape, except for 50% tint, is the same for all screen angles and frequencies, dot is non-directional so it is less affected by press problems. Shadow dots are less prone to dot gain - especially in a film workflow – than the simple Round dot.
Issues: optical bump occurs at 50% midtone tint which puts it in the most important and visible image tones.
Elliptical dot (a.k.a. Transforming Elliptical Dot, Chain Dot): Rounded corner diamond shape
Benefits: Optical bump is moderated by being split into two – when the dots first touch at the long width at the 40% tint and then again at the short width at 60%.Issues: dot shape varies at different screen angles which can cause single color moiré and uneven dot gain. Dot is directional, at low lpi frequencies the “chaining” of the dots as two points touch can cause lines to appear as artifacts. Directional problems on press such as slur and doubling can cause strong tone and color shifts depending on the angle of orientation of the dots relative to the angle of the paper as it travels through the press.
Square dot: Square
Historically used for catalog work, letterpress, and specialty work.Benefits: Gives an impression of a "sharper" looking image on press thus reducing the need for excessive sharpening in image editing applications.
Issues: Very prone to loss of shadow detail due to very thin spaces between shadow dots.
Line dot: Line
Historically used for newspaper work, lenticular, and specialty work.Benefits: At lower screen rulings can have a strong graphic effect.
Issues: Directional problems on press such as slur and doubling can cause strong tone and color shifts depending on the angle of orientation of the lines relative to the angle of the paper as it travels through the press. Directional lines can introduce very visible subject moiré. Image edges can appear ragged.
Specialty dot:
Any custom dot shape designed to meet specific requirements.
Benefits: Halftone dot optimized for specific applications.
Issues: Requires extensive knowledge, development time, and testing in prepress and pressroom in order to implement.
Here are two examples:
Pepper Dot:
Uses small dots within larger conventional dots in order to reduce ink usage on press – especially for newspaper work. (Click on image to enlarge)Novelty Dot:
Uses a recognizable image or graphic to form the dot. (Click on image to enlarge)
Friday, February 20, 2009
The Wayback View - Graphic Arts Training
Gather a group of printers around the table to discuss the business issues they face and one topic that's sure to come up is the problem of today's graphic arts training - or, more often, the lack of training in their typical customer. They'll complain that today's creatives don't know anything about what it takes to prepare art for their presses. They will share tales of designers who supply art for a company's Annual Report in PowerPoint format, or the 200-page, fully illustrated catalog created in a shareware word processor and saved across 30 floppy discs.In today's digital world, it seems that anyone with access to a computer can call themselves a designer and the printer is expected to happily receive their files and automagically go to press with them. Unfortunately, more often than not, those files are not even close to being ready for production. Instead, the printer's prepress department must often take on the task of rebuilding the files to prepare them for the press - usually without being able to charge for this service. Print shop owners will wax nostalgic about how much better it was in "the good ol' days" when skilled technical people created press-ready artwork for them.
Interestingly, the good ol' days may not have been that different from the reality of today. Following is a short letter to the editor that appeared some 86 years ago on the topic of graphic arts training - it could have been written yesterday.
"Because I have recently declared in one of our daily papers that our system of art and graphic art education is wrong, I have been plunged, immersed, turned over and over, in hot water.
It is essential that the school of art must give the commercial artist the right preliminary training. And what should that be?
The first step is a change of outlook. It is critical that the student artist be taught that his skills must first of all serve the needs of commerce.
The next step towards making the complete commercial artist is to enable him to become thoroughly acquainted with the methods of production. One of the most serious defects in the present system is that students are pouring from the schools to join the army of work seekers and find themselves but ill-equipped to do the work they seek. Young artists who know nothing of the means by which their ideas have to be produced. It is not just now easy for them to obtain inside knowledge. Manufacturers are secretive - and often look on the creative artist with suspicion and even contempt.
The art masters, the students, the printers, and manufacturers must learn to understand each other and work together. Equip the student with the right point of view towards commerce, the right perspective, and the right technical training, and commercial art will attain new heights of achievement. And print manufacturers themselves will profit by this new relationship with the creative artist through more efficient production methods and happier results for all."
- Charles A. Farmer
- Published in Commercial Art First Series - 1923
After 80 some years, it appears that the old adage that "the more things change - the more they stay the same" still applies.
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