Hybrid AM Screening/XM Screening - Addendum, part 3

In the Addendum, part 2 I looked at the published specifications from the various CtP vendors to determine whether they provided information about their CtP device imaging capability and hence whether there would be a need for a Hybrid AM/XM screening workaround for specific devices. In general, the information they provide is quite vague. So, in this post I'll be looking for that information in the published specifications for plates.

A bit more resolution detective work

Once again Kodak (followed closely by Agfa) is the top vendor as far as clarity and consistency of stating their plate resolution capability is concerned. From the information they provide one can tell exactly what the resolution limitation of their plates are (e.g. Agfa :Amigo supports a 21/25 micron minimum dot and requires a Hybrid AM/XM screen to go above 200 lpi – the same goes for Kodak Electra Excel.)

Some vendors provided either no, or vague information (e.g. Fuji Brillia Thermal: "Excellent tone and dot reproduction", Heidelberg: No information provided)

So, as with the CtP devices, in order to determine the imaging performance of most of the CtP plates on the market, you will need to engage a sales representative to provide you with a clear statement and specification in writing.

However, you can also run some tests yourself to validate the vendor's CtP imaging and plate combinations. To do that you will need a test target such as the PIA/GATF Digital Plate Control Target.The digital file provides a means of monitoring exposure level, checking imaging resolution, diagnosing directional effects or image inconsistencies.

Validating CtP device/plate resolution capability

The Digital Plate Control Target should be imaged at 5 locations on the plate – the center and four corners. After the plate is processed the targets are checked under a loupe to determine the resolution capability of the CtP/plate combination. There is an informational box in the test target that lists, among other things, the horizontal and vertical resolution as well as direction of travel through the imaging device which is helpful in interpreting information provided by the various targets.

Horizontal and vertical microlines
These are examined visually and provide a quick indication of the exposure level and resolution capability of the CtP/plate combination. If the CtP device images at 2,400 dpi then each 1 pixel microline will be 10.6 microns thick (1% dot at 240 lpi). Proper exposure is indicated when the positive and negative microlines are imaged at the same width. If the one pixel lines are not rendered this indicates a resolution limitation with that particular CtP/plate combination. In that case, check the two or three pixel lines instead to determine the resolution threshold. Also note if the vertical and horizontal microlines are rendered equally well. Inconsistencies with imaging vertical and horizontal microlines indicate directional differences in the output system.

One pixel through four pixel checkerboard
This target is extremely sensitive to the resolution capability of an imaging device. Nearly all CtP/plate combinations will have trouble rendering the 1x1 pixel checkerboard sharply. If the overall appearance of the checkerboard is indistinct with soft edges between the positive and negative pixels, then the resolution of the CtP/plate combination has been exceeded. Due to their lack of resolution, many CtP/plate combination cannot successfully image less than the three pixel checkerboard at a 10.6 micron pixel size.
Put another way, they cannot resolve halftone dots made up of less than three pixels and as a result require a Hybrid AM/XM solution to recover highlight and shadow tones between 1% - 3% and 97% - 99% when the screen ruling is finer than about 175-200 lpi. They may also be restricted as to whether they can do FM screening and/or the level of fineness of FM screen they can reliably image. On a related note, it is argued by some vendors that because it is the consistency of imaging of the perimeter of the halftone dot - made up of 10.6 micron pixels - that determines the consistency of halftone dots throughout the tone scale, an inability to reliably and consistently image the 1x1 pixel checkerboard indicates a CtP/plate combination that is not optimal as far as delivering consistent plates to the pressroom is concerned.

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Below, in alphabetical order, is the list of vendors and plates I checked, including the specifications they publish either on their web site or in their brochures.

Agfa :Amigo: Resolution 1-99% with :Sublima 240, 200 lpi. 25μ FM
Agfa :Ampio: Resolution 1-99% dot rendering at 200 lpi
Agfa :Azura: Resolution Up to 2-98% at 200 LPI depending on imaging conditions
Agfa :Energy Elite: Resolution 1-99% at 200 lpi. FM and :Sublima 280 lpi capable depending on platesetter
Agfa Lithostar Ultra LAP-V: Resolution 1%-99% at 200 LPI

Fuji Brillia Thermal: Excellent tone and dot reproduction

Heidelberg: No information

KodakElectra XD: Resolution 1% to 99% @ 250 lpi with Kodak SQUAREspot Imaging Technology, FM capability 10 micron stochastic
Kodak Thermal Platinum: Resolution: 1% to 99% @ 400 lpi dependent upon capability of imaging device. FM capability 10 micron stochastic dependent upon imaging device capabilitites and screening algorithms.
Kodak Electra Excel: Resolution: 1% to 99% @ 200 lpi. Dependent on capability of imaging device. FM capability 20 micron stochastic. Dependent on screening algorithms.
Kodak Sword Excel: Resolution 1% to 99% @ 200 lpi. Dependent upon capability of imaging device. FM capability 20 micron stochastic. Dependent upon screening algorithms.
Kodak Thermal Direct: Resolution 1% to 99% @ 175 lpi; 1% to 98% @ 200 lpi. Dependent on capability of imaging device. FM capability 25 micron stochastic. Dependent on screening algorithms.
Kodak Thermal Gold: Resolution 1% to 99% @ 250 lpi. Dependent on capability of imaging device. FM capability 10 micron stochastic. Dependent on screening algorithms.
Kodak Violet Print: Resolution 2% to 98% @ 200 lpi, platesetter dependent.

Presstek Aurora Pro: Resolution 1% - 99% @ 200 LPI or FM
Presstek Anthem Pro: No information
Presstek Freedom Pro: Resolution 2%–98% @ 175 LPI

Southern Lithoplate Viper: Resolution 1-99% @ 200 lpi Screening FM Screening Certified
Southern Lithoplate Cobra: 1-99% @ 300 lpi FM Screening Certified