~~~~~~~~ Excerpt from the Guide to Platinum Palladium Photographic Printmaking by Jeffrey D. Mathias ~~~~~~~~
No part of this document may be reproduced in whole or in part without the express written permission of the Author.
created September 2000, updated April 2001

 
Appendices
to Building
Digital Negatives		 Building Density Steps
Building a Gradient
Optimizing the Original Negative for Scanner Noise
Puddling
Registration
Resolution
Sharpening


Building Density Steps:
Density Steps are used during Curve Calibration in place of an original negative.  It is important that Density Steps be built using the same film, chemistry, equipment, processing, and exposure as would a typical original negative.

The steps are exposed as follows:

Processing and exposure must be that given for a typical for a full range negative with typical normal contrast and as would be used to scan and produce digital negatives.  This includes accounting for Optimizing the Original Negative for Scanner Noise.




Building a Gradient:
The gradient and step bars built here are used throughout the digital negative calibration procedure.  The 1% step gradient will be the most useful during calibration.
  • In Photoshop, Open a new image 10 inches high by 0.5 inch wide at 600 ppi in RGB mode;
  • set the background color to C0-M0-Y0-K0;
  • set the foreground color to C0-M0-Y0-K100;
  • build a 0.5 inch wide, 10 inch vertical gradient bar using the Gradient Tool;
  • save this as the Photoshop gradient;
  • change the canvas to 10 inch by 1.5 inch keeping the gradient to one side;
  • Open a new image 10 inches high by 0.5 inch wide at 600 ppi in RGB mode;
  • in the new area select 100 adjacent areas of 0.1 inch by 0.5 inch and fill with 1% increments of density with the paint bucket, one at a time.
  • save this as the 1% gradient;
  • select all, copy, paste, and move opposite the Photoshop gradient;
  • using the 1% gradient select five blocks at a time and fill with 5% increments of density;
  • save this as the 5% gradient;
  • select all, copy, paste, and move between the other gradients;
  • flatten and save as the Original Gradient.
    • Original Gradient
    Figure 7:  Photoshop gradient, 5% step gradient, and 1% step gradient subsequently called Original Gradient




    Optimizing the Original Negative for Scanner Noise:
    Just as it is so very important to customize the original negative for the selected printing process, so too it is important to produce the proper negative for scanning.  Those who have used a scanner to record the information from a negative should be familiar with the relationship that bit depth of the scanner must be increased as the dynamic range of the negative increases.  If the bit depth does not increase, vital information from the negative will be omitted from the scan.  This information likely first disappears under a level of noise.  Next the information becomes limited because a certain number of bits can only provide a certain number of tones and the image requires a certain
    number of tones be present so that posterization effects are kept hidden.  Posterization is not eliminated in a digital negative, only minimized to a fine enough level.  (The actual desirable number of tones is not known at this point.)

    To determine proper dynamic range and processing requirements of the negative, several negatives were made at the following developments.  The film used was 4x5 Kodak Tri-X exposed at 200ASA.  The first number is development time in minutes with continuous gentile agitation in a tray (one negative at a time).  The second number is the concentration of the HC-110 developer in ml/litter.  A Zone VI temperature compensating timer was used.

    3@32
    4@32
    5@32
    6@32
    4@64
    5@64
    6@64
    7@64
    A typical full range Pt/Pd print would have the negative processed at 5@64 (this may vary with the use of different equipment, Pt/Pd materials, or procedures).  The dynamic range of these negatives increases as one moves down the list.  This is the usable, practical dynamic range.  Any range adjustment due to base plus fog is considered negligible for this study.  Any density beyond that related to Zone XII is dismissed as not practical to use.  Zone XII is considered because a palladium print can easily produce all those zones.

    Each of the negatives was scanned with 12-bit pixel depth and converted and stored as 8-bit (the way of the HP ScanJet 6300). The closest negative with the highest dynamic range and without noise in the highlights was found to be 5@32 (this is about half the processing given to a typical Pt/Pd negative).  The noise would appear at the same density, so as each negative that had more dynamic range, more of the upper end would consist of noisy data.

    Data from two of the negatives can be found below in Figure Opt1.

    It is true that the noise can be smoothed out with various software techniques, but regardless the original data covered by the noise is corrupted and lost.

    A similar evaluation can be made by scanning a Stouffer 21-step.  Find the densest step that does not show noise and that density will relate to the maximum density of a film processed a certain way.  Note that the actual film used is a better test as the characteristics of the Stouffer 21-step may be different, however densities can be evaluated fairly easily with the Two Hole Method.  An example using the 21-step can be found below in Figures Opt3 and Opt4.

    CONCLUSION:
    In order to get optimum results it is recommended to match the negative's dynamic range with the scanning equipment used.  A dynamic range too high will result in the loss of information, most likely from the highlights.  A dynamic range too low will result in wasted data capacity.  It would be preferable to error too low so as to maintain image integrity.

    Just to give something additional to ponder:
    It is guesstimated that a typical negative made for Pt/Pd printing would require 14-bit data without noise.  If it is assumed that 2 bits will contain noise (typical), then a 16-bit scanner should be sought if one wishes to scan negatives that also typically are used to print with the Pt/Pd process.

    More to ponder:
    It is not known if or what differences a Pt/Pd print may exhibit between using a 16-bit scan from appropriate negative and a 12-bit scan from appropriate negative.  It is suspected that a negative with a higher dynamic range may enable a higher print quality.  It is not known, but could be possible that this is part of the reason for a Pt/Pd print to have better tonal separation than some other processes.  This comparison could also be made controlling built analog negatives.

    Detail of Negative 5@32Detail of Negative 5@64
    Figure Opt1:  Negative (5@32) processed at half that typical for Pt/Pd (left).  Negative (5@64)
                            processed as typical for Pt/Pd (right).  Note corruption of critical highlights (not pure
                            white sky).  The two 4x5 negatives are scanned with a 12-bit scanner, with all features
                            such as noise reduction and  sharpening turned off, and the exposure adjustment set
                            full range, and at 1200 ppi, full color with zero saturation.  A portion of each negative
                            containing some critical highlight values is cropped and compared.  The levels are
                            then adjusted to better view the noise.  The banding patterns are an indicator of noise,
                            likely due to a low signal level of the detectors.
    full 4x5 negative indicating position of detail
    Figure Opt2:  Full 4x5 negative indicating the portion
                            selected for the detail in the upper right.



    21-step scanned at 12-bit
    Figure Opt3:  A 21-step is scanned with a 12-bit scanner, with all features
                            such as noise reduction and sharpening turned off, and the
                            exposure adjustment set full range, and at 1200 ppi, full
                            color with zero saturation.
    step containing noise
    Figure Opt4a:  The lowest density step containing noise is identified.

    enhanced image of noise
    Figure Opt4b:  The levels are adjusted to better view the region around this step.

    each step normalized to better disclose texture
    Figure Opt4c:  Each step is adjusted to a similar brightness so that the texture may be clearly seen.
                              The banding patterns are an indicator of noise, likely due to a low signal level of the
                              detectors.  In this example, step 12 is the density at which the noise level just begins
                              to cover subtle tone variations.




    Puddling:
    Puddling is the result of ink flowing on the substrate in areas significantly larger than the desired resolution.  The follow is used to check both Puddling and resolving ability.



    Registration:
    The following are registration procedures for two methods of digital negative building.

    Stacked Negative registration begins with the formation of alignment marks on the negatives.


    Tri-Negative registration begins with the formation of alignment marks on the negatives as above.  Follow the seven steps above figure Reg1.


    Resolution:
    The resolution should be ultimately determined by the substrate selected for the Pt/Pd print, it is important to have enough resolution in the scans of the original negative as well as the prints of the  negatives.  Look below for a comparison of prints using digital negatives as a function of the resolution at which the digital negative is printed.  A resolution of 600 ppi for the final print size seems to be a good choice.
  • In Photoshop open a new file with a resolution of 600 ppi (or higher, if the equipment is capable).
  • Using the line tool draw several lines with a width of 1 pixel and spaced 1 pixel.
  • Using the line tool draw several lines with a width of 2 pixels and spaced 2 pixels.
  • Using the line tool draw several lines with a width of 4 pixels and spaced 4 pixels.
  • This will produce targets of 600 lpi, 300 lpi, and 150 lpi respectively.  (lpi = lines per inch, lines are both black and white).
    • resolution targets
    Figure Res1:  Targets of 600 lpi, 300 lpi, and 150 lpi (enlarged to 72 ppi)
     
    Pt/Pd print of resolution targets
    Figure Res2:  1200 ppi scan of Pt/Pd printed targets (enlarged to 72 ppi)
                         The substrate is Crane's "Cover-90" paper.
                         The Hewlett Packard DeskJet 970 (used to print the digital negative) has a benefit
                         of being capable of printing the same lpi (lines per inch) as the dpi (dots per inch).
                         When this paper is to be used with a negative from this printer, scan resolution
                         should be 600 ppi and printer resolution 600 lpi.

    comparison of Pt/Pd prints from negatives printed at various resolutions
    Figure  Res3:  Comparison of Pt/Pd prints from digital negatives printed at various resolutions.
    The original Pt/Pd print detail (left) is from a print of the sister original negative.  The others are details of the Pt/Pd prints from digital negatives printed at the indicated resolutions.  The original negative scan was at a resolution of 600 ppi.  The Pt/Pd print details were all scanned at 1200 ppi and sharpened an equivalent amount.

    Note that the original contains much more detail.  This level of detail may be hard to discern when viewing the actual 4x5 print.  However, there is a noticeable difference in texture and tactile quality amongst the prints.  It is possible that some lack of detail may be due to slight registration misalignment of the negative stacks.  The higher resolution negatives were easier to register.  The 300 ppi and 150 ppi negatives had more sharpening applied than those of 600 ppi (some bar effect is noticeable).  [It is recommended to use minimal sharpening for actual negatives.]

    It is also noted that the printer may not have been producing the 600 lpi it is supposed to, which could likely be due to dot gain.  Although tests at the maximum ink levels showed the printer to print lines at 600 lpi resolution without puddling or blotches.



    Sharpening:
    Sharpening should be kept to a minimum and an adequate sharpening threshold level used to help avoid posterization.  It seems that any amount of sharpening will tend to encourage posterization.  Setting the sharpening threshold to higher values may help reduce posterization.


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