The eternal conflict - ink/water balance - the tale of the tones

An AM/XM halftone screen has a builty-in conflicting ink/water balance requirement on press. The highlight dot and quarter tone range from 1-35% requires minimal water and maximum ink in order to prevent those dots from being washed away. The three-quarter tone range from 65-99% requires the opposite - a larger volume of water in order to prevent the shadow dots from filling in and disappearing. On the other hand, the mid-tone range from 35-65% is more of a balance between ink and water.

Halftone dots and the tones range they represent are affected differently by the condition of the ink on press - assuming of course, that the plate, press, and chemistry are set up correctly. Unfortunately, if the press operator attempts to fix tone reproduction in some areas, that built-in difference in ink/water requirement can exaggerate the inherent conflict and cause problems in other parts of the tone range.

1 - 1-35% This tone range is primarily affected by the body/viscosity of the ink. If the body is too soft the highlight area will print too full which may cause the press operator to decrease solid ink density in order to reduce the dot size. Alternatively the fountain solution may over-emulsify this tone range causing poor ink transfer and loss of highlight detail. If the ink body is too heavy the dot may print too sharp causing the press operator to increase the density or blanket pressure.

2 - 35-65% This tone range is primarily affected by the strength (pigment load) of the ink. If the ink is too weak the press operator will increase solid ink density which will cause increased dot gain and result in presswork that appears too full. If the ink is too strong the midtones may print too light. Also, the strength of the ink also impacts how well the inks trap, which in turn affects the color gamut the press should be able to achieve. Varying the strength and stiffness of the ink to achieve good tone reproduction in presswork is a method press operators, who don't have good communication with prepress, often employ. It's almost always better to use tone reproduction curves applied in plate imaging than to modify inks.

3 - 65-95% This tone range is most strongly affected by mechanically induced dot gain or chemistry issues i.e. (poor ink water balance). If the tone range from 1-65% is evenly balanced then excessive gain in the shadow tones is usually caused by running excessive water, too much blanket pressure, and/or mechanical slur.

FM Screening - Second Order 20 micron FM/Stochastic Screen

[click "Play" to view animation - may take a moment to buffer]
This is a second order FM screen (Kodak Staccato). In a first order FM screen, dots of the same size are added to simulate darker tones. In a second order FM screen, dots of the same size are added to simulate darker tones – however at a certain tone value no more dots are added. Instead the existing dots simply grow, in one or two directions, in order to simulate darker tones.

"DPI" and the misuse of graphic arts terminology

The prepress and press worlds are some of the worse misusers of terminology with the all too frequent resulting confusion in sales, marketing, specification, and production. Here is one of the most misused: "DPI" (or as it is spoken of in the rest of the world: DPCM).

"DPI" - Dots Per Inch is a term used for a variety of things that properly speaking it shouldn't.

DPI - when used to describe the resolution of a computer to plate imaging device or filmsetter. E.g. "This is a 2400 dpi CtP device."

"Dots" in this case refers to the laser "Spots" of energy that expose the printing plate or film. However, while DPI, identifies the number of dots per inch - it doesn't actually describe the resolution of the device or size of the spot of energy. Instead it defines the device's "addressability." In other words, dpi tells you how many locations per inch a spot of energy can be focussed on – not the actual size of the spot of energy.

This graphic shows plate media being exposed at 2,400 dpi by six different CtP devices:Note that they are all 2,400 dpi - that is that they all can hit the target location (address) with their beam of energy - however the exposing spots of energy are all different sizes, in this example ranging from about 2 microns on the left to about 30 microns on the right.

Resolution vs addressability is explained in more detail by clicking HERE.

DPI - when used to describe the resolution of an inkjet printer. E.g. "This inkjet proofer prints at 2880 x 1440 dpi."
In the case of an inkjet printer, the clue to this misuse of dpi to wrongly mean resolution is revealed with asymmetrical dpi specifications. So, an inkjet proofer that has the specification that says it prints at 2880 x 1440 dpi does not mean that the resolution is finer, or that the droplets of ink are finer in one direction. Instead it simply means that the paper is moved more slowly in one direction - i.e. the addressability is changed - while the physical size of the droplet of ink, and hence its resolution remains the same.
On the left a symmetrical inkjet addressability grid (600 x 600 dpi). On the right the same printer set at 1200 x 600 dpi. The addressability has changed but not the size of the cyan droplet of ink and therefore the actual resolution of the device remains the same.
In any case, the actual size of the mark the droplet of ink makes on the paper is unknown. For a 600 or 1440 "dpi" ink jet printer it most certainly is not 1/600ths or 1/1440th of an inch in size. As a result, with some inkjet printers, reference is sometimes made to "picoliters" in addition to dpi when the resolution of the device is described in the specifications. A picoliter is a unit of fluid volume. A lower minimum ink volume tends to yield a smaller minimum droplet size of ink allowing more dots of ink to be in the same area thereby yielding higher actual resolution. While picoliter is a better indicator of the relative size of the splat of ink on the paper it is still a unit of volume and not area. So it suggests a difference in resolution but doesn't actually specify it.

DPI - when used to describe the resolution of an image scanner. E.g. "This is a 600 x 2400 dpi scanner."
An image scanner—often abbreviated to just scanner—is a device that optically scans images, printed text, handwriting, or an object, and converts it to a digital image. The resolution of Digital images is usually expressed as dots per inch or pixels per inch. As a result the resolution of scanners is often expressed in terms of dpi (and sometimes "ppi" pixels per inch). The more accurate description is "spi" which stands for "samples per inch" since scanners sample the document they are scanning.

A related issue with defining scanner resolution is that manufacturers typically refer to the scanner's interpolated resolution - which is a software upsampling algorithm method to increase the pixel density - instead of using the scanner's true optical resolution. If the scanner's dpi is asymmetrical (e.g. 600 x 2400 dpi) then the smaller number usually indicates the particular number of individual samples that are taken in the space of one linear inch while the larger number is the interpolated samples.

DPI - when used to describe the resolution of an image. E.g. "This is a 300 dpi image."

Once an image has been digitized, either via scanning or captured with a digital camera, it is in the form of a raster image made up of pixels (picture elements). In graphic arts usage the pixels are typically square in shape and 8-bits (256 grey levels) in depth per channel (greyscale = one channel, RGB = three channels, CMYK = four channels).

Because pixels are generally thought of as the smallest single component of a digital image, the more pixels that are used to represent an image, the closer the result can resemble the original.As ppi, a.k.a. "dpi", increases so does the amount of image detail that can be rendered creating the impression of greater apparent resolution.Pixel counts can be expressed as a single number, e.g. an image at 100% reproduction size being 300 "dpi", or as in a "three-megapixel" digital camera, which has a nominal three million pixels, or as a pair of numbers, as in a "640 by 480 display", which has 640 pixels from side to side and 480 from top to bottom (as in a VGA display), and therefore has a total number of 640 × 480 = 307,200 pixels or 0.3 megapixels.
Again, the measures dots per inch (dpi) and pixels per inch (ppi) are sometimes used interchangeably, but have distinct meanings, and although dpi is often used to refer to digital image resolution the proper term is "ppi" - pixels per inch.

Analog FM screening

I've been using FM screening in presswork since 1970 (kindergartens were very sophisticated back then :-)). This was way before PhotoShop, personal computers, and digital workflows. The method I used was fairly simple, but difficult to perfect.

I would take a conventional low contrast 35mm black and white (or color slide) positive image.

I would then place the piece of film in my enlarger in the darkroom.

Then I would project the image through a piece of frosted glass that had the frosted side in contact with a piece of lithographic film.Lithographic film does not record grey levels - just black and white. It is the same film that printers use to expose their printing plates.
The rough surface of the frosted side of the glass acted like a digital threshold array and broke the image into a random halftone pattern where the frequency of the dots (and to a lesser extent their size) represented the different grey levels of the original image.The coarseness of the frosted side of the glass determined how coarse the resulting "FM" screen was.

The final result was a piece of negative film that my printer would strip into the the job and use to burn the printing plate.

I see halftones everywhere!

Technically speaking, halftone screens are "tessallations" - patterns that cover a surface by the repeated use of a single shape, without gaps or overlapping. And since tessallations are popular decorative items - I end up seeing halftone screens everywhere. Here are a few from a recent trip to Seattle.

A classic Diamond halftone dot

An example of a high lpi traditional Square dot halftone

In contrast to a very low lpi Square dot

Waiting to cross the street I spot a mix of two halftone patterns
At first it appears to be a classic Round dot mixed with a more subtle Square dot halftone
But on closer examination it seems to be an exotic version of Esko's Concentric screening. Interestingly the pixels that make up this sidewalk halftone are round instead of the traditional square shape.

Walking past this building reveals a fine example of
Second order FM/stochastic screening.
Sometimes the final halftone screen is not visible, but instead, you can see the foundation for the halftone. Halftone screen dots are formed by a "threshold" array - basically a pattern made up of 256 shades of gray which determines which pixels are turned on to form the actual dot.
The tones of the granite pillar on this building

Make a great threshold array to create a
Mezzotint halftone (the right half of the photo below - click to enlarge)

How AM and FM screening equivalencies are measured

I'm often asked about what AM/XM halftone screens are equivalent to a certain FM screen - i.e. "What AM/XM screen is equivalent to a 20 micron FM screen?"

There are two ways that this halftone screening equivalency is usually measured.

One is equivalency of detail rendering - the ability of the screening to render image detail. The other is lithographic equivalency - how they perform on press lithographically. Note that in both cases, because the respective screening technology is so different, equivalency can only be an approximation.

Equivalency of detail rendering
Since halftone dots form the printed image - more dots per linear inch translates into more detail that can be rendered.

With an AM screen the detail rendering ability is specified in lpi (or lpc) - i.e. halftone dots per inch (e.g. 175 lpi or 60 lpc).

Since an FM screen has no "lines per inch" determining the equivalent detail rendering equivalency is usually done by drawing a line through the FM screen and counting how many dots are intersected (crossed) in a distance of one inch.Measuring the relative lpi of an FM screen.
The above example shows an FM screen enlarged. The distance measured is 1/16th of an inch. In that 1/16th of an inch approximately 36 dots are intersected. So, in one inch about 576 dots would be intersected (16 x 36). Put another way, there are 576 dots per linear inch - 576 lpi - to render detail, i.e. this FM screen is equivalent to a 576 lpi AM/XM screen.

Lithographic equivalency
Lithographic equivalency is a bit more complicated to figure out. It is usually measured by counting the number of edges (transitions) in a square inch.Measuring the number of edges of an AM/XM screen.
Measuring the number of edges of an FM screen.
Halftone screens with a similar number of edge transitions will have similar lithographic properties.

AM/XM equivalents of some popular FM screens.
Keep in mind, these are approximations only, however they do give a good indication as to screening performance.

To linearize your CtP plates or not?

A bit of background
Back in the old film to plate days the standard prepress procedure was to linearize film output. That means a specific tone request in the original file results in halftone dot in the film equal to the file tone request. So, for example, a 50% in the file became a 50% tone in the film. Linear film was the agreed standard interchange file format between prepress tradeshops, publishers and printers. At that time, the final tone on the plate was not measured. Instead, the resulting tone in the presswork was measured and deemed to be in specification, or not, relative to the supplied linear film. I.e. At 133 lpi, a 50% tone in the film resulting in a final tone of about 71% in the presswork would be considered in specification. Interestingly, although the film was linear, the resulting plates were not linear due to the dynamics of exposure in the vacuum frame.

The arrival of CtP in the late 1990s eliminated film as the intermediary. As a result, measuring tone values on the plate became a process control metric. However, CtP plates seldom have a linear response to laser exposure and if a tone reproduction curve is applied to them to make them linear - the resulting presswork is usually too "sharp" - i.e. not achieving enough dot gain.

At the same time that CtP was rapidly being adopted, printers also began to use finer halftone screens, including FM screens, which had very different dot gain characteristics compared to the old published standards. Printers began to leverage the flexibility that CtP provided in being able to apply different tone reproduction curves to their CtP plates to achieve the tone reproduction on press that they required.

So the question for the printer becomes: should prepress first apply a curve to linearize the plate and then, if needed, apply another curve on top of the first to achieve the desired final press tone response?

I was shocked
So, just to confirm that the method that I have been using for the past 13 years was indeed the standard method used in the industry, I posed the question to an internet printer's forum: "Do you linearize your plates before applying a press curve (a two curve workflow - e.g. one to linearize the plate followed by another one to compensate for dot gain) or do you only apply a press curve to the uncalibrated plate (a one curve workflow - e.g. one to compensate for dot gain)?"

The response shocked me - a whopping 70% said they first linearized the plate with a curve and then applied a press curve while only 30% responded that they simply applied a press curve to the uncalibrated (natural state) plate.

70% using one curve on top of another? That makes no sense to me at all.

In a film to plate workflow, linear film is exposed to the plate in a vacuum frame. The function of the plate exposure is to reproduce the halftone dots in the film as consistently as possible across the surface of the plate, and perhaps more importantly, to create a robust halftone dot on the plate that will maintain its integrity on press. However, although the film may be linear, the resulting plates are not linear due to the dynamics of exposure in the vacuum frame. In North America using negative film there is typically a 2%-5% dot gain on plate at 50% (i.e. 50% in the film creates about a 54% on the plate) while in Europe and Asia where positive film was used there is typically be a 2%-5% tone loss at 50%.

In a CtP workflow, as with a film to plate workflow, the important thing is to set laser exposure and processing (or lack thereof) to the manufacturer's specifications so that the result is a robust halftone dot on the plate that maintains its integrity on press. However, as with a film workflow, the resulting plates are typically not linear due to the dynamics of laser exposure, individual plate characteristics, and processing.

In this example, the thick line that dips below the 0 line is the natural uncalibrated plate curve after the engineer has done their work setting up exposure and processing for the most robust dot possible.With this particular positive thermal plate the uncalibrated plate curve results in a negative value through the tones. The bottom numbers in the graphic are the requested tone values in the file - 5%, 10%, 20%.... 90%, 100%. The "0" line represents linearity. I.e. if the plate was linear then that 0 line would be straight and be the "plate curve". But, in this case, a 50% request has resulted in about a 47% on plate. This is fairly typical - a well and properly exposed CtP plate does not have a linear response (i.e. a straight line). Also note that it is typically not a classic Bell curve - there is no symmetry. Different CtP/plate combinations will each have their own characteristic natural curves.

So, from a CtP vendor engineer's perspective, it does not matter whether the result of their setup is a linear plate or not since a tone reproduction curve can always be applied to achieve whatever tones are required on plate - including linearizing the plate. What's important is that the exposed dot is robust and that the plate imaging is consistent across the plate and repeatable from plate to plate.Put another way - the key criteria is that when properly set up the plate will have a characteristic non-linear tone response. And that's fine - as long as the plate responds the same - i.e. delivers the same non-linear tone response – every time because without that consistency it is not possible to build any tone reproduction curves at all.

Some definitions

These definitions are not "official" however they are useful to keeping the issues and discussions clear.

A "plate curve" is a tone reproduction curve that is applied in the workflow to a plate in order to have it render tone values that are different from those it delivers when the laser exposure and processing (or lack thereof) have been set to the manufacturer's specifications. So, applying a linearizing curve that makes an inherently non-linear plate linear is an example of the use of a plate curve.

A "press curve" is a tone reproduction curve that is applied in the workflow to a plate in order to have it render tone values that are required to deliver a specific tone response on press. The assumption is that the laser exposure and processing (or lack thereof) have been set to the manufacturer's specifications.

By this definition, if only a linearizing curve is applied because a linear plate is needed to deliver the correct tone response on press then that linearizing curve is a press curve.

A plate curve in this sense is not related to tone reproduction on press. It is effectively a calibration curve. It brings the plate to a known condition. However, in a CtP environment, the manufacturer's setup of laser exposure intensity, processing chemistry, and processing time effectively calibrates the plate plate to a known condition. It might not be linear but it is known. There is no need to recalibrate by applying a plate curve to what is already calibrated.

Another way to look at the question

Let's suppose that a linear plate provided the tone response on press that we need. Would it make sense to then use two curves - one to linearize the plate (a plate curve) and a second curve (a press curve) to linearize the linearized plate? I doubt it. Makes more sense to just apply the one linearizing curve - based on the uncalibrated natural condition of the plate.

So, if that logic makes sense, why wouldn't it make equal sense if we needed a non-linear press curve? Just apply the one non-linear press curve based on the uncalibrated natural non-linear condition of the plate.

As long as the plate's tone response is consistent then it can be the basis on which to build press curves. However, if the plate is inconsistent in its tone response then the use of linearizing plate curves as well as the use of press curves will fail. You cannot use curves, plate or press, on a device that is inconsistent.

What the "authorities" have said*Some quotes on this topic from the Idealliance G7 guides:

6.2 Origin of NPDC curves
To determine the 'natural' NPDC curves of commercial CtP-based printing, G7 research analyzed numerous press runs made with ISO-standard ink and paper, and a variety of plate types imaged on “un-calibrated” CtP systems (no RIP curves applied, not even to “linearize” the plate).

5.4 Set up the RIP
Set up the plate making RIP exactly as you would for a normal job, but clear out any values in the current calibration table, or begin with a new, empty table. The first press run is best made with ‘un-calibrated’ plates – i.e. no calibration values in the RIP.
IMPORTANT: Do NOT linearize the plate-setter so that measured dot values on plate exactly match original file percentages. Contrary to common belief, this may reduce accuracy of subsequent steps.

a. PRINTING IDEALIZED TARGETS VALUES - Achieving calibration condition with raw or linear plates, not requiring a curve, is an ideal situation.

*A note about authorities. I had trepidations about including these points from G7 because I do not believe that people should blindly do what some authority says they should do. It is not enough to say "Do it this way because I say it should be done this way." If the authority cannot explain exactly why one way is wrong and another right then it is just an opinion and without evidence to back it up it is not a credible opinion. I included these quotes only because they may carry credibility for some readers of this post.

Scenarios“We’ve always done it this way!” or “This way works just fine!” Even when we have the time to think about how or why we do things a certain way, our thoughts are often clouded by that kind of thinking. However, it can make it easier to understand the merits of a one curve workflow compared with a two curve workflow if one breaks down the sequence of steps required to get a plate into the press room. Given the same final result, the fewer the steps - the better the workflow since it provides fewer opportunities for error.

Here are some examples of workflow scenarios to see what happens with a one curve workflow vs a two curve workflow:

One CtP & one plate shop - to achieve the same final result on press:
One curve workflow: one press curve = one curve total.
Two curve workflow: one linearization plate curve plus one press curve = two curves total.

One CtP & one plate shop using three different curves to optimize for three different papers. To achieve the same final result on press:
One curve workflow: one press curve per paper type = three curves total.
Two curve workflow: one linearization plate curve plus one press curve per paper type = four curves total.

One CtP & two plate shop - to achieve the same final result on press:
One curve workflow: one press curve per plate type = two curves total.
Two curve workflow: two linearization plate curves plus one press curve = three curves total.

One CtP & two press shop - to achieve the same final result on two presses:
One curve workflow: one press curve per press = two curves total.
Two curve workflow: one linearization plate curve plus two press curves = three curves total.

One CtP & one plate shop - what happens if a new batch of plates do not perform as the previous batch did:
One curve workflow: modify one press curve so that the plate tones are the same as the previous plate batch = one modified curve total.
Two curve workflow: modify one linearization plate curve plus apply the standard press curve so that the final plate tones are the same as the previous plate batch = two curves total.

One CtP & one plate shop - what happens if the press curve needs to be tweaked/adjusted:
One curve workflow: modify one press curve to achieve the required tone reproduction on press = one modified curve total.
Two curve workflow: one linearization plate curve plus modify one press curve to achieve the required tone reproduction on press = two curves total.

One CtP & one plate shop - what happens if the CtP device is replaced:
One curve workflow: measure the new plate output and modify one press curve to achieve the same tone reproduction/dots on plate as with previous CtP = one modified curve total.
Two curve workflow: measure the new plate output and modify the linearization plate curve to linearize the plate then apply the existing press curve = one modified curve for two curves total.

Looked at this way, the linearization plate curve, in the vast majority of cases, is redundant. It serves no useful purpose except to add complexity and another point of failure.

Esko Concentric screening - some observations

Esko Concentric screening is at heart an AM screen which uses a unique halftone dot where solid AM dots are divided into thin concentric rings.Click on the above image to see it enlarged.
Concentric screening and color gamut
Chroma in press work derives primarily from the ratio of light being filtered by ink carried on halftone dots vs light reflected off the paper that hasn't been filtered by the ink. Light that is unfiltered by the ink effectively contaminates the color reducing the potential gamut of the inks. If one compares Concentric halftone dots with conventional AM/XM halftone dots at the same lpi - e.g. 175 lpi. what is clear is the difference in ink coverage area through which light can be filtered.
At left is a micro photo of Esko Concentric and on the right is an AM/XM screen (Esko Paragon). Both are imaged at 175 lpi.
Note that dividing the dot into rings actually lessens the area of ink and increases the area of unprinted paper. Effectively it increases the contamination of color by light reflected off of the unprinted substrate which can actually reduce, rather than increase, the potential gamut.

In the below plot, the CIEL*a*b* values of the same tone values for 175 lpi AM/XM/Paragon screening (in green) is compared to 175 lpi Concentric (in red). If the Concentric had a larger gamut the red dots would be significantly above the green dots indicating a greater chroma. Instead they track at, or are below, the chroma for 175 lpi AM/XM/Esko Paragon screening.
What this means is that, as far as I can determine, Concentric screening offers no additional gamut, and possibly less of a gamut, when it is compared with AM/XM screens at the same lpi.

Concentric screening and image quality
Since it is still an AM screen there is still the opportunity for screening and subject moiré - although the finer the screen (AM/XM or Concentric) the less likely that will be a problem. Because it's still an AM halftone screen it has rosettes - just like any other AM/XM screen - formed by the screen angles.At left Esko Paragon AM rosettes. At right Esko Concentric rosettes. Both screens are 175 lpi. (Squint your eyes or move a few feet away from the screen to make the rosettes more prominent.)
From a print buyer point of view there will likely be no visible difference between a 200-300 lpi conventional AM/XM screen and Concentric screening - even if viewed under a loupe.

Concentric screening and ink reduction
The two primary causes of the reduction in ink usage with high lpi screens are the thinner ink films and the need for tone reproduction curves for plate imaging to bring the press tone response in line with the standard 175 lpi AM/XM screening. Ink reduction with the use of Concentric screening should be similar to the ink reduction enjoyed by high lpi conventional AM/XM as well as FM screens.

Concentric screening and on press color stability
Greater color stability when solid ink densities naturally vary during the press run is a characteristic of high frequency screening (i.e. smaller dots) whether AM/XM, FM or Concentric. The actual ink film thickness of Concentric vs conventional AM/XM screening at the same lpi is actually very similar. Projecting dot density to height in 3D one can see this quite clearly (Concentric is left of the black line - AM/XM is right of the black line.)Of course, if the Concentric screening is run at a very high lpi it will acquire a stability that is similar to conventional screens (AM/XM and FM) that are run to the same high frequency.

Concentric screening and imaging system resolution
Concentric screening is effectively an AM screen ruling multiplier. What this means is that the resolution of the imaging system needs to be able to image the minimum specified ring width. Put another way, if the ring thickness called for is 10 microns wide then the imaging system (plate and press) must be capable of consistently imaging a 10 micron pixel/dot even though the actual final halftone dot size may be almost five times wider (e.g. 48 microns wide a 50% dot at 250 lpi).Concentric halftone dots that depend on 1-2 pixel width imaging integrity can be problematic for most imaging systems
As a result, using Concentric screeing can push the effective screen frequency so high that process stability and imaging may be compromised and it can be difficult to support their use on plate let alone find a way to implement them in the press room. The problem is that some concentric screen settings can drive rulings way over what plate imaging can support - on the order of 1-2 pixel widths for the rings, which is understandably problematic. For example, a 200 lpi screen with 2 pixel ringwidths = 600 lpi which is finer than, for example, a 10 micron FM screen.

Coarser ringwidths are easier to support but at that point it is probably more effective to use an AM screen of equivalent lpi.

For printers contemplating the adoption of Concentric screening
Since Concentric screening is a conventional AM screen using a unique halftone dot design, I suggest that when you are evaluating this type of screening that you "compare apples to apples". That means that you should compare the on press performance of Concentric against a conventional AM/XM screen imaged at the same lpi. Use a combination of subjective (pretty pictures) as well as objective measurable targets (single and two color step wedge gradients and IT8 profiling targets).

N.B. The data that I used as the basis for this post is derived from published promotional samples printed by Esko. I have contacted Esko as well as members of public prepress/press forums asking for press profiles and/or printed test samples of Concentric vs conventional AM/XM screens run at the same lpi under the same press conditions. Despite the product being in the market for over four years I have been unable to acquire such a basic color profile or press samples. If you have that data I would appreciate hearing from you by email ( pritchardgordon @ gmail (dot) com ).

Halftones as you've never seen them before

I use a variety of image analysis tools when investigating how different halftone screening solutions perform. These tools are normally used in the medical field to do image analysis of microscope acquired imagery. However I press them into service to analyze various aspects of halftone dot structures.

Here is a microscope view (200x) of a conventional AM/XM printed halftone dot (175 lpi elliptical):
And here's a microscope view (also 200x) of a 20 micron FM screen:
One of my favorite tools is to use image analysis software to project the pixel density values in the images into height - creating a 3D image that shows the relative ink density (ink film thickness) differences between the two screens. The thicker AM/XM:vs the thinner FM:Using color mapping instead of the actual ink color makes the difference in ink film thickness even clearer (yellow = greatest - blue= lowest ink film density):Lowering the viewpoint and warping the perspective of the 175 lpi AM/XM screen begins to turn the image into a kind of landscape: However, using terrain mapping software on those original microscope images of the AM/XM and FM screens really makes the transformation of the images into proper landscape views a reality.

175 lpi elliptical dots:
Sunlight across a deep FM canyon:
A low flight over a a barren land where FM and AM screens meet.
Sunrise over an AM screen mesa.
Moonrise over an FM peak.
FM screen hits the wall.

Planet Round Dot.

And if you have a pair of these:
You can add a bit of dimension to your halftones:
Of course, this is all very serious work - not fun at all. Really. ;-)