Introduction:
The nature of the platinum/palladium process
requires that a contact print be made. Thus the size of the print
is restricted to being the same size as the negative. To make a larger
print, a larger negative must be made. As always, there are many
ways that this can be accomplished. The methods
described here are only preliminary and have not met the criteria for a
negative suitable for the Pt/Pd process.
The two general methods available for building
negatives are digital and analog. The Analog Method consists of enlarging
and exposing by optical means onto photographic film and is the subject
of Chapter 12. The Digital Method optically scans an original into
bits electronically stored on a computer, manipulates the data by software,
and prints a negative with ink on a transparent substrate using a printer.
The digital method is discussed in this chapter.
There are several methods to make a digital
negative. Many factors are involved with the building of a digital
negative. A decision was made to utilize readily available equipment
designed for the home office that could get the job done and avoid depending
on services from others. The two methods described
below have merit but have fallen short of producing negatives suitable
for the Pt/Pd process. The primary deficiency
is with producing enough tones so as to avoid noticeable posterization.
These methods require the evaluation of
Pt/Pd prints to calibrate and determine adjustments; one must already be
proficient with the Pt/Pd process.
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Considerations:
Resolution - of the scanner
and the printer must be able to provide the minimum of detail printable
on the selected paper (see Resolution
Appendix). A rough surface paper can allow for a lower resolution,
while a smooth paper may require a resolution greater than available.
A diffuse light source and a rougher paper may hide the loss of resolution
when contact printing. If more detail is desired from a detailed
negative, the sun can be utilized as the light source.
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Ink Density - of the digital negatives
must be great enough to allow a maximum white in the print while producing
a maximum black. This is a major consideration since most printers
will not deposit enough ink at the resolution desired and most inks are
not opaque enough with the light used to expose the Pt/Pd coating.
This may be resolved by building a stack of several negatives (as with
the Stack Method) or by using ink or multiple inks that can achieve the
necessary opaqueness.
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Registration - is important and
is related to the particular method of negative building. When several
exposures are given to a single coating from several negatives, each negative
must be be accurately registered with the coating. This can be accomplished
by aligning two adjacent sides of the negatives and the print substrate.
When several negatives are to be stacked
together, they can have registration marks added to facilitate alignment.
Registration details can be found in the
Registration
Appendix.
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Posterization - is the clumping
of closely related continuos tones into discrete steps. All tones
can be considered posterized to some level. What is important is
the threshold level of posterization at which the eye can discern a difference.
Below this threshold the tones appear continuous. Above this threshold,
steps may become detectable, fine texture or subtle variances of tonality
may be lost, or a sterile unphotographic look may result.
There must be a sufficient number of individual
tones usefully spread throughout the printable range of the negative so
as to avoid noticeable posterization. At this time, it is not known
how many tones are necessary or what the distribution should be.
The number of tones per Zone (density ranges of the Zone System) likely
varies as well with a greater number of tones required in the mid Zones.
An increased number of tones can be achieved
when several negatives from several scans are stacked or individually exposed
onto the Pt/Pd coating. However, 16-bit data scanned, manipulated,
stored, and printed seems the best solution. This can provide 14-bit
real data with 2-bits of noise separation.
Currently scanners are available that provide
16-bit data. Some 16-bit software exists (GIMP)
and seems to be moving in this direction. However, reasonably priced
printers have yet to come close.
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Calibration - address several concerns
and is a vital and useful part of building negatives. All calibrations
are evaluated using Pt/Pd prints. The negative building parameters
set by calibration may vary with the original negative, Pt/Pd printing
parameters, and desired results. The calibrations are performed in
the following order.
Color Mix Calibration - selects colors and
inks and their mixture to determine the control of the tones and keep colors
within gamut of the printer.
Maximum Black Calibration - has two parts.
Part 1 is dependent on the negative substrate and the total exposure given
(Total Printing Exposure). Part 2 involves the minimum amount of
ink to produce a discernible threshold above Maximum Black, is termed the
Maximum Black Threshold, and occurs after the Maximum White Calibration.
Maximum White Calibration - determines the
maximum amount of ink (subtractive) and/or the minimum exposure (additive)
that must be controlled so as to provide the lowest print density.
With multiple exposures, this may require an adjustment to the Total Printing
Exposure producing an Adjusted Total Printing Exposure.
Maximum Black Threshold - (see Maximum Black
Calibration above)
Base Curve Calibration - produces a set of
standard curves to be applied to every negative set. One purpose
is to adjust the Maximum Black Threshold without losing the Maximum Black
and provide the desired shadow detail. Another is to normalize the
distribution of data throughout the full range so as to produce the tones
(both values and amounts), local contrasts, and range desired in the print
for a typical original. It is important to distinguish Base Curve
Calibration from Creative Control. It is likely that every image
will require tweaking (Creative Control) to arrive at a desired result.
The first draft should have a standard applied (Base Curve Calibration)
so as to provide for a starting point having minimum influence of the equipment
and materials used to get from the original negative to the negatives producing
the Pt/Pd print.
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Boundary Conditions - characterize
the limits of a particular function and provide insight as to the control
of that function. Several follow which are usefull with building
digital negatives and on which the calibration procedures are based.
Resolution - The resolution of the final
print should be limited by the substrate used. The scanner, software,
and printer should have resolution capability at or better than the substrate
offers. A lack of resolution may not be apparent as a loss of detail
in the final print without magnification, however it is likely that the
lack of resolution will be apparent as a lessening of texture, tactile
quality, and tonal discrimination. The resolution must be actual
physical resolution of the devices and not interpolated.
Selection of Ink (and/or printer) - It
would be most desirable to have a multi-shade UV/blue light blocking ink
with high resolution print head.
Maximum White - Enough density of ink must
be built up in the digital negative(s) so as to produce a complete absence
of print density (paper white). Too little ink will result in an
inability to obtain a pure white in the print while maintaining the Maximum
Black. Too much ink will result in a merger of the upper values into
pure white and a reduction of the total number of independent tones.
(Too much ink may also cause puddling and a loss of resolution or fine
discrimination of detail; see Puddling
Appendix.)
Printing Exposure (Maximum Black) - Enough
exposure must be given to the Pt/Pd print so as to achieve a Maximum Black
with a given negative substrate (includes base plus fog). Too little
exposure will result in a Maximum Black which is noticeably too light and
an image which may be muddy, have a loss of range, lack detail in the dark
values, or be without a black anchor to reference other dark values.
Too much exposure will result in the dark values merging into the Maximum
Black and a lowering of all values, and the contrast of the Pt/Pd print
may also be reduced, but with the sacrifice of lower density negative information.
Maximum Black Threshold - There is a certain
density (ink amount) which will provide a shade of black in the print which
is noticeably lighter than maximum black. This value is a function
of personal preference as well as the discrimination provided by the materials
used. Too low of a threshold (lower ink amount) will cause the lower
values to merge into Maximum Black. Too high of a threshold (higher
ink amount) will cause less range of ink density and a reduction in the
total number of independent tones.
Number of Tones (Posterization) - There
are a certain number of tones in the total range and in specific sub-ranges
(Zones) of the final print which are required to avoid detecting posterization.
The number of tones produced in the print are a function of the number
of tones in the digital negative minus those below the Maximum Black Threshold,
assuming correct Printing Exposure and Maximum White Calibration.
Too few tones will result in noticable posterization. Too many tones
will result in excessive information to be stored and handled. The
number of tones can dramatically be restricted by the scanner, software,
and printer. If the equipment has shortcomings, procedures might
be able to overcome them. The Number of Tones may also be lessened
by any software operations including, but not limited to, curve adjustment
and sharpening.
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Methods:
The methods described
have been fully developed and carried out, however only a summary is given
as neither method has produced prints of acceptable quality. The
primary definciency is too great a level of posterization. Each method
has significant merits and could be usefull with the proper reduction of
posterization.
Stack Method:
This method produces three negatives separating
the low-mid, high, and upper densities of the original which are then stacked
together and exposed as a single negative to the Pt/Pd coating. The
Stack Method, in effect, produces a single density from which to expose
a Pt/Pd coating.
Each range of density is scanned from the
original negative, the data manipulted, and each printed. Then the
printed negatives are registered and fastened together and used as if they
were one negative.
Click here for a detailed explination of the Stack Method.
Multiple or Tri-Negative
Method:
This method produces three negatives emphasizing
the low, medium, and high density ranges of the original which are then
exposed one at a time onto the Pt/Pd coating. The Tri-negative Method
produces three full range negatives which emphasize the low, mid, and high
ranges of the original and then exposes them onto a single Pt/Pd coating
one at a time.
Three scans with various gamma adjustment
are made from the original negative, the data manipulated, and each printed.
Then the printed negatives are used one at a time, in registration, to
expose the Pt/Pd coating.
