Using a densitometer to measure plates

Despite what you may have heard from vendors - yes, you can use a densitometer to read offset plates. This can be especially helpful for the smaller printshops who may not have the resources to purchase dedicated plate readers.

Densitometer basics

Color reflection densitometers are designed to accurately measure Black, Cyan, Magenta, and Yellow colorants on substrates like paper. However lithographic plates usually don't have C, M, Y, K images on a white substrate, instead the plate material is usually brushed aluminum with a grey color. The color of the image itself will vary according to the plate type and vendor.

You need to be aware of these reflectance and color properties since they effect how you use your densitometer when evaluating your plates.

Contrast

Because of plate color properties, the contrast between image and and non-image areas of the plate is typically less than half that of ink on paper, as a result it may not be possible to calculate dot area for some densitometer/plate combinations.

Aperture size

The densitometer aperture (measuring window) should be the largest possible for your brand of instrument - as long as it's not larger than the image area you are measuring. This helps average out the reading and minimizes the effect of random plate patterns.

Densitometer Status

The instrument should be set to "Status T" unpolarized in part because this setting has a wider response to the various plate coating colors.

Consistency is more important than absolute accuracy

Conventional and digitally imaged plates typically use the same aluminum base material. However the different types of mechanical or chemical graining that prepares them for lithography results in a different surface texture which in turn scatters light differently. In order to achieve consistent dot values. To help achieve consistent dot value measurements, you should try to maintain a consistent alignment of the densitometer to the plate. Perhaps using the base of the densitometer aligned to the edge of the plate. Also, zero the densitometer and read the 100% area on the same spot each time and take readings from the center of each target patch.

If you know that a patch on the plate represents a 50% tone (i.e. it is a checkerboard) but your densitometer reports the patch being, for example, a 54% tone while the plate prints correctly on press then 54% becomes the target for that patch on the plate. The idea is that you are controlling your plate imaging process by monitoring and minimizing variation. Your priority is to maintain consistency in the measured dot areas.

Alternatively you could change the dot gain calculation "N" factor. Densitometers use one of two formulas for measuring dot area; the Murray-Davies or the Yule-Nielson equation. They are the same equation however the Yule-Nielson equation utilizes an "n"-factor to "factor" out the optical dot gain (the Murray-Davies equation is equivalent to the Yule-Nielson with n set to 1.00). The n-factor is experimentally determined by adjusting it until the densitometer reads the ‘desired value’ at a known dot percentage. Typically a 50% tone is used because it is easy to spot. You'd print a number of tone values close to 50% (e.g.45% and 55%) then use a loupe to find the tone patch that ‘looks like' a 50% tone - a checkerboard. Next adjust the n-factor on the densitometer until that patch reads 50%. The n-factor is typically applied when a densitometer is used to measure printing plates since printing plates are assumed not to have any optical dot gain.

Print buyers, dollars, and sense

Print buyers often say their purchase decision is based solely on price – even when they know it’s not true. Unfortunately, print salespeople, brainwashed by hearing this over and over again, tend to believe the buyer. Buyers know the strategy works – so they use it. Counter this argument with a total value approach.

Print consists of product and service. Analyze the customer’s success factors for the project in product and service terms. Look beyond what the customer says is important to include criteria from similar projects as well as the customer’s history. Look beyond the cost of your part of the project and look at what you could do to reduce the buyer’s overall project cost. Your print quote should reflect the customer’s unique needs and objectify the value you bring to the table by putting a dollar value on the benefits the customer will receive by dealing with you.

When you get the job, make sure that the reasons for getting the job are communicated to everyone in the production process so that they can help validate, through their work, the buyer's decision to award their business to your shop.

Choosing the right screen angle for over-printing spot colors

To decide which screen angle to use when a screened PMS/spot color overprints a 4/C process image you will need to look carefully at the image that you will be overprinting.

The basic rule is to use the screen angle of the least prominent (or missing) screened process color that will be underneath the screened spot color.

For example, if there's no screened black under the spot color - use the Black angle, if there's no Cyan use the Cyan angle, etc.

Try to avoid using the Yellow screen angle because in standard screen angle sets yellow is only 15 degrees away from C or M. As a result moiré is always there but it is usually not visible because the yellow is so pale. The moiré can become visible however, if the yellow becomes contaminated - or if it is used for a dark spot color.

For example, in the graphic below, the left image is Cyan (at 105°) overprinted with process Yellow at the standard 90°. The moiré is barely visible. However, in the center image overprinting Cyan with PMS 144 – a very dark yellow/orange color – using the same Yellow screen angle results in the existing moiré becoming very visible. On the right, PMS 144 uses the Magenta screen angle (75°) instead which eliminates the halftone moiré seen in the center image.

Alternatively, you could try running the 5th color using a second order FM screen. If you're using a 175 lpi AM/XM screen then the FM should be about 35 micron because if it's any finer you'll need to create dot gain compensation curves for the FM. Because 35 micron is a fairly coarse screen it is best used for fairly light colors otherwise you may find that the screen is too visible.

Because spot/PMS colors are typically formulated to be printed solid and not halftone screened, make sure that your ink vendor knows that you are going to be screening the ink and the dot size range as well (either in microns or lpi) so that they can formulate the inks accordingly.

Know your customers

When a customer places their print order, the company has an opportunity to find out much more about customer preferences than it could ever learn through traditional market research. Even when a project is lost to a competing printer, there is an opportunity to learn a great deal about the competition. Hunches and feelings are no substitute for hard data, so gather in a database as much information about customers as possible. Building relationships is the key to success and those relationships depend on intimate knowledge. You could potentially profile your customers, workflows, and presswork so that in the future you will be better able to tailor production and service for each customer and each project. Referring to this information can also lead to better-tuned estimates, guide new equipment purchases, and suggest new service opportunities.

Printing prepress - literally

A fascinating insight into how production printing was done before mechanized printing presses that is still being done today.

Founded in 1729, The Derge Parkhang is the last remaining Tibetan printing temple of its kind. The Parkhang stores more than 300,000 woodblocks that are used to publish sutras, commentaries and histories of Tibetan Traditional Buddhism.


Please press the play arrow to view the video. Note that it may stop for a moment while the video buffers in the background.
More information can be found on the Derge Parkhang YouTube channel by clicking HERE.

RE:Print - "Scheduling"

"Click image to enlarge"

Sharpening images - creating detail by destroying detail

Many graphic arts professionals aren't aware that image quality very often depends on optical illusions. One optical illusion in particular, "Mach bands", is critical and fundamental to quality image reproduction.

Mach bands are named in honor of Ernst Mach the Austrian physicist and philosopher who is also the namesake for the "Mach number" (also known as Mach speed). The Mach band optical illusion is the basis for how most image sharpening, such as the "UnSharp Mask" filter in Adobe Photoshop, is effected in photo editing software.

The principle idea is that we do not see detail because of our eye's resolving power but because of tonal contrast. For example, this is an image of a wall beside an electrical socket. The lighting used was very low contrast:
Here is the same section of wall but this time using low angle lighting:
Obviously the texture of the wall hasn't changed, instead what has changed is the tonal contrast of the area and that allows us to see the texture detail.

Mach discovered how our eye/brain leverages contrast to compensate for its lack of actual detail resolving ability.

Look closely at the below image which has nine patches of grey set between a black patch and a white.

Do the grey patches appear scalloped? Lighter on the left than on the right? In fact, the grey patches are of a uniform tone as can be seen by simply moving one patch out of its context.

The scallop effect is an optical illusion. To make up for our eye/brain's detail resolving deficiency it processes incoming light in such a way as to exaggerate the contrast wherever two different tones meet. Increasing the contrast at those edges gives us the perception of more detail.

Here's how the sharpening filter in Adobe Photoshop leverages this optical illusion to make images look more detailed. First I'll apply it to the original grey patches. The top half is the original and the bottom half with the sharpening filter applied:

What PShop does is to increase the contrast at the border between different tones by creating synthetic Mach bands.

Now we'll see the same sharpening method applied to a real image.
On the left is an original globe image straight out of the camera. On the right is the globe after sharpening is applied showing the effect of creating Mach bands with image sharpening.
Click on image to enlarge

Here is a close-up section of the globe images to more clearly show the difference:
Technically, the sharpened image actually has less real detail because image pixels had to be converted to black and white lines bordering the actual image detail. However, despite having less detail our eye/brain perceives a sharper, more detailed, image all thanks to software leveraging the power of an optical illusion.

Print is a Craft. Print is a Science.

Printing is traditionally thought of as a craft-based industry. However, with print manufacturing becoming increasingly digital and automated, and processes more scientific and objective, it can be hard to see any room for craftsmanship remaining in the process.
Consider that print production actually begins in the mind of the creative designer. From the printer’s point of view, the process of translating those ideas and expectations effectively into ink-on-paper value begins at the earliest stages of the sales cycle – the project brief or request for quote.
The printer’s craft is critical in the relationship between sales, planner, and customer. It is the craft of forging effective communication, the conversion of concept into specifications, the weighing of options, and the art of negotiation.
And because no press design nor press environment is perfect, the printer’s craft is still critical in enabling the press operator to maintain the customer’s presswork intent and expectations as they are translated into ink on paper – despite all the variables that can impact presswork integrity.