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PROCEDURE
to Build a Digital Negative by the Stack Method:
This method produces three negative elements (a low to mid tone range Base Negative, a high tone range High Negative, and a upper tone range Upper Negative) which are stacked together and printed as a single negative.  Three scans are made, one for each tone range, and three digital negatives are printed and used with one exposure to the Pt/Pd coating.

The resulting prints from this method have failed to be of acceptable quality due to:
posterization - likely restricted by printer, driver, and inks and perhaps 8-bit software
lack of detail - likely restricted by printer, driver, and the physical stack exposed using
                         UV lamps
lack of texture - likely restricted by posterization and lack of detail
However, it it felt that this method can succeed with proper printer, inks, and software.

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ORIGINAL NEGATIVE:
It is imperative that the original negative be optimized for the scanner used.  Basically the negative should have the greatest dynamic range of densities and the maximum density should permit a scan signal uninfluenced by noise.  Click here for a study of scanner noise and optimizing negatives.  A typical negative for use with the Pt/Pd process will likely require a 16-bit scanner, assuming 2-bits are relegated to noise suppression and 14-bits are accurate data.  If less bits are available, then the negative must be processed with less of a total range.

Figure 1:  Full scan of an original negative.

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SCANNING:
Scanning reads the information contained in the original negative and places it into a digital data file.  It is important to scan in full color with the color saturation set to zero, at maximum pixel depth, with the selected exposure range (see below), and at a resolution suitable for the final print size (see Resolution Appendix).  Sharpening should be set to none.

Position original negative on the scanner as for a transparency scan, tape to glass, and mask all area except negative with opaque material.

 

Perform preliminary scan.

 

Set the Exposure Adjustment, Input Levels for one of the three scans:

1023 to 4095 for the Base Negative

255 to 1023 for the High Negative

0 to 255 for the Upper Negative

NOTES:

Setting the levels should normalize the data as described below in Normalization.  Normalization equates the range of the original negative and the scanner.

The division between Base and High Negative (1023 value) may be altered during creative manipulation.

The upper range may be set at values larger than 0, if the dynamic range and maximum density of the original negative is lower than the capability of the scanner, but keep the range width of 256.

The base range may be set at values lower than 4095, if the dynamic range of the negative is lower than the capability of the scanner or in situations of much base plus fog.

If data is eventually converted to 8-bit (as with Photoshop and most printers), keep any additions or subtractions of the range values to multiples of 16.  The will help avoid round-off errors.

Carefully selecting the exposure adjustments can normalize the data here instead of in the software (see Normalization below).

Negative is scanned (using the settings above and in Equipment Setup) by the scanner stand alone software and saved as a tiff file (include some film edge and some opaque area when doing calibrations).  Stand alone operation will better assure that the scanner settings remain constant and each scan mechanically proceeds from and over the same position.  Include a boarder for easier registration (see Registration Appendix).

 

Save as a tiff file.

 

Perform the other two scans changing only the Exposure Adjustment, Input Levels.

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Software Manipulation: (for each of the three negatives):

Open file

 

Change Mode to 16-bit

Note: 16-bit mode will avoid round off errors causing a loss of data when
           changing modes or applying calculations.
 

Change Mode to CMYK

Note: The proper CMYK color setting (GCR Maximum) should place all the
          data in the K channel.

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Normalization (optional):
This step is optional at this position and should have been performed during the scanning (Setting the Exposure Adjustment, Input Levels).  Normalization equates the range of the original negative and the scanner.  Normalization selects the maximum black and white points of the print while selecting a range of values contained in the original negative.  The end points and range selected may differ from the range of the negative.  End points selected beyond the range of the negative will result in maximum tonal values in the print which are gray.  End points selected within the range of the negative will result in a print with values from black to white but will include only the selected portion of the negative.  (NOTE: It is important to select the exact limits of printable white and black.  This is an important part of this procedure which likely differs from other methods.)

This step should be used to fine tune exposure which has been properly scanned.  Most films will produce densities exceeding the requirement of Pt/Pd coatings so over exposure can be corrected without a loss of total tonal range in the print.  However, underexposure may result in an unrecoverable loss of information from the shadows.  To adjust for over exposure use the white point dropper to select a value in the negative to be set to the limit of maximum black in the print.

 

Selecting the unexposed film edge with the white point dropper automatically compensates for any film base plus fog.

 

Alteration of contrast (overall or local) should be accomplished by the use of curves or layers later.

 

To reduce the overall tonal range in the print (end points selected beyond the range of the original negative), it is suggested that new calibrations be used instead.  This will help keep the number of individual tones maximized and provide for better tonal discrimination in the print.  Note that normalization may also be performed with the scanner and may provide better data.  Normalization will allow for a standard set of calibration and curves to be applied to produce a consistent standard print with a standard range of values ready for any desired optional creative control.

 

Image, Adjust, Levels - set white point dropper to 0%C, 0%M, 0%Y, 0%K and set black point dropper to  0%C, 0%M, 0%Y, 100%K.

 

Use the white point dropper to select the lowest negative density which should represent the maximum printable black (film edge or as desired and may be used to alter the original exposure).

 

Use the black point dropper to select the highest negative density which should represent pure white or paper base in the print (opaque area or as desired and may be used to adjust the range of values).

 

Apply the levels after optionally saving the level information.  It is likely that each original will require unique levels.

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Color Mixing:
Color Mixing is a simple but important step that selects the inks to be used.  It is very important that colors are selected so that the entire range of values/colors will be within gamut of the printer.  If not within gamut, the color may be arbitrarily changed or assigned the same value as another.  (See Calibration Procedure.)

Image, Adjust, Channel Mixer

 

Load the saved Mixer data.

 

Apply

 

SAVE as a psd file.  This file is a backup of the unmanipulated data.

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Standard Curve Adjustment:
Curve adjustment performs several tasks.  For the Base Negative, it provides a steep ramp to bring ink densities to a level which provide discernible tones while maintaining a Maximum Black.  For all negatives, it provides for contrast control and local creative control.  A separate standard curve should be applied first producing a standard print from which creative control may depart.

Image, Adjust, Curves

 

Load the appropriate standard curve.

 

Base Curve as determined by the Base Curve Calibration.  This should provide the lower values (about Zone 0 through Zone V) for a full range print.

 

Curve for the High Negative (may be omitted).

       In Cyan and Black channels, change all output to 0.
       In CMYK and Magenta and Yellow channels, leave as straight 1:1 line.
       This should provide the high values (about Zone VI to Zone VIII) for a
        full range print.
 

Curve for the Upper Negative.

       In CMYK, leave as straight 1:1 line.
       In Cyan and Black channels, change all output to 0.
       In Magenta and Yellow channels, enter the curve formed when a point is
       added  for input=80 output=93.
       This should provide the upper values (Zone VIII to Zone XII and beyond)
        for a full range print.
 

Apply the curve.

       NOTE: The standard curves should be used for every corresponding
                    negative.  For each original an additional curve may be added
                    specific to that particular image.
 

Image, Adjust, Curves

 

Make any creative modifications, adjustments, or refinements, save this curve information separately, then apply the curve.  The step may be repeated after a print is made.  This is the reason for saving the curve information.

CLICK HERE to compare figures 4 and 5 (before and after the standard curves are applied).

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Optional Creative Control:
This is the best place for creative control with other 16-bit tools.  Save file first.

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Printing Preparation & Output:

Change Mode to RGB

 

Change Mode to 8-bit

 

Optional Creative Control: Save file first.

 

Sharpen with the unsharp mask.  How to do this can be found from many sources.  Sharpening is highly likely to further posterize the image, reducing the number of tones.  Be cautious to keep sharpening to a minimum (see Sharpening Appendix).

 

SAVE the final file.

 

Print on substrate with the settings determined by calibration.

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Pt/Pd Printing:
The resulting negative is assembled and printed with the materials and technique used for calibration and the exposure determined during calibration.

Position the negatives on a light table and tape together in the following order.

 

With ink side down, place Base Negative on light table,

 

register the High Negative to the Base Negative and tape,

 

register the Upper Negative to the others and tape,

 

use the stack of three as a single negative.

 

Print with the settings indicated above and from calibration.

NOTE: For best resolution use a collimated light source such as the sun.
             With a diffuse light source (such as a bank of BL bulbs), papers with
             a rougher surface will show a lower resolution than that lost from not
             having complete contact, as do the High and Upper Negatives.
             Paper selection should take the resolution into account.

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CALIBRATION  PROCEDURE:
These calibrations should be completed in the same order that they are presented here.  The calibration is based on an already determined Pt/Pd procedure of fixed materials and methods.  Any deviations from this fixed Pt/Pd procedure may require a new calibration or adjustments.  The examples and actual values given are specific to the materials, equipment, and settings used for this procedure and may differ.  It is imperative that one do their own calibration.

Only the final Pt/Pd print can accurately depict results, and only final Pt/Pd prints are used to make decisions concerning calibration and the procedure.   Calibration of the monitor is only necessary with a desire to preview the image on screen and may be beneficial to preview creative manipulations.  The monitor should not be used for calibration.

It is important that all equipment be synchronized so as to not arbitrarily alter selected color values.  This can be accomplished through color management selections.  All equipment used was set to function under sRGB color management as default.  Also, some Photoshop parameters and settings must be carefully controlled.

Important NOTE: This procedure and examples herein discussed produce a full range print.  If another range is desired, modifications should be made and calibrations and settings should be altered accordingly.  For example, if one wishes a limited range print (such as restricted to Zones IV to VI), the maximum black threshold can be raised and the maximum ink density lowered which would preserve achieving the most individual tones.

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Color Mix Calibration:
The purpose of the Color Mix Calibration is to utilize more than one ink for a more diverse set of printable ink tones while making sure that colors (tones) do not become altered by being out of gamut.  Most printer drivers and Photoshop will change an out of gamut color to a closest color within gamut.  This can cause several tones to be represented as a single tone.

Note: The RGB color setting and profile must be set to sRGB which is the default factory setting for the HP DeskJet 970 printer.  If another printer is used with a different color setting, use that color setting throughout.

open original gradient (see Gradient Appendix);

 

change to 16-bit mode;

 

View, New View to create a new view;

For the new view: select View, Gamut Warning and View, Preview, Cyan.

Make sure the preference setting for gamut color is cyan.

change to CMYK mode;

 

Image, Adjust, Channel Mixer - adjust as follows:

        Output           Source
        Cyan             Cyan=0, Magenta=0, Yellow=0, Black=0
        Magenta       Cyan=0, Magenta=0, Yellow=0, Black=+100
        Yellow           Cyan=0, Magenta=0, Yellow=0, Black=+100
        Black            Cyan=0, Magenta=0, Yellow=0, Black=0
NOTE:  This mix of color should produce some out of gamut steps on the
              gradient for a sRGB color setting.
 

change to RGB mode;

 

check the new view image for any out of gamut indication (any cyan, even slight);

NOTE: The gamut can only be checked in RGB mode.
 

change to CMYK mode;

 

Image, Adjust, Channel Mixer - Vary the Black source amount for outputs Magenta or Yellow, switch to RGB mode, check gamut, and repeat until the entire gradient is within gamut (no Cyan on the new view);

 

change to 8-bit mode;

 

print.

 

 

Repeat with another mixture until the color mixture producing the smoothest and most complete gradient is found.   The goal should be to use as much ink as possible while remaining within gamut and producing a gentle gradient.

This example settled on the following mixture:
          Output               Source
          Cyan                 Cyan=0, Magenta=0, Yellow=0, Black=0
          Magenta           Cyan=0, Magenta=0, Yellow=0, Black=+90
          Yellow               Cyan=0, Magenta=0, Yellow=0, Black=+100
          Black                Cyan=0, Magenta=0, Yellow=0, Black=0
 

Save the Channel Mixer settings for easy recall as these will be applied as a standard to every negative.

NOTE:  It may be necessary to start over and redetermine the Color Mix, if
              the Base Curve applied later throws the colors out of gamut.
 

Save the color mixed gradient for use in the calibration of the Maximum White and Maximum Black Threshold calibrations.

Figure 7:  Original gradient (top) - Gradient after Color Mixing (bottom).

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Maximum Black Calibration (1^st of 2 parts):
Calibration of Printing Exposure:

Make a Pt/Pd print using a stack of three pieces of blank substrate intended for the digital negative covering half the coated area. Expose at various times incremented by 0.5 stop intervals (steps).  Choose times so that at least two steps are identical between the areas covered and uncovered by the substrate;

 

Select the step with the longest exposure that is identical between the areas covered and uncovered by the substrate;

 

Including and starting with the selected step, make another print with at least five exposures at increasing increments of 0.1 stops;

 

 

Select the step with the longest exposure that is identical between the areas covered and uncovered by the substrate.  The exposure of this step is the Printing Exposure.  This will assure that Maximum Black is possible in the print with the shortest exposure.  The black chosen for Maximum Black will likely not be the absolute black the materials are capable of producing, but should be reasonably close.

Figure 8:  Determining Printing Exposure to give Maximum Black for the substrate used.
                The bottom is an enhanced copy of the top in order to better discern differences.
                 Note the horizontal pencil marks on the sides indicating the edge of the substrates.
                 For the example, the Printing Exposure is determined to be at most 6.5 minutes
                 (as 6.0 minutes shows slightly lighter, and 7.5 minutes is about the same).  Note that
                 the materials may produce even more density beyond Maximum Black.

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Maximum White Calibration:
This will adjust the maximum amount of ink the printer will be set to print which will govern the Maximum White produced for the determined Printing Exposure.

In Photoshop, Open the gradient produced in the Color Mix Calibration;

Note that the densest portion of the gradient should produce Maximum White in the Pt/Pd print.
 

increase the Canvas Size, Copy, and Paste so that three gradients are on the page;

 

Print (using settings indicated in setup above).

 

Separate and register the three gradients and tape together.

 

Place an opaque sheet adjacent to and along one side of the composite gradient.

 

Make a Pt/Pd print with the coating behind the gradient and opaque sheet, exposed for the Printing Exposure determined above.

NOTE:  One of the final gradients will be used later for the Maximum Black
              Threshold and Base Curve calibrations.

Using the Pt/Pd print, find the position on the gradient at which there is only the slightest difference between the gradient and the opaque sheet.  If this position is not adjacent to the end of the gradient (highest density), then go to “DECREASE” below.  If there is no white on the gradient, go to “INCREASE”  below.

INCREASE:

In Photoshop, in the Printer Setup, set the Ink Volume heavier or select a paper that is setup to use more ink (matte or plain papers are generally set by HP to use more ink).

 

 

Finer control is achieved by going heavier than necessary and then reducing the ink by the Transfer Function in Page Setup.  To do so reduce the 100% value to a lesser value.

DECREASE:

In Photoshop, in the Printer Setup, set the Ink Volume lighter or select a paper that is setup to use less ink.

 

For fine adjustment, in Page Setup, use the Transfer Function to reduce the maximum amount of ink.  To do so reduce the 100% value to a lesser value.

 

Repeat the above until the Pt/Pd print shows Maximum White (paper white) only at the densest step of the gradient.

NOTE:  Too much ink can result in the ink puddling which may cause defects in the
              highlights of the print.  These defects can be spotted if desired.  Too little ink
              will prevent a pure white from being produced in the print.  The elimination of
              the unused inks, cyan and black, helps to reduce the total volume of ink and
              helps prevent puddling.
              Puddling can be checked as outlined in the Puddling Appendix.

Figure 9:  Using Pt/Pd print of the gradient to determine Maximum White (red indicator) for
                adjusting maximum deposition of printer inks.  This example used the equipment settings
                described above.

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Maximum Black Calibration (2^nd of 2 parts):
Calibration of Maximum Black Threshold:

Retrieve one of the final gradients also containing blank substrate from the Maximum White Calibration above and use it, stacked with two blank substrates, to make a Pt/Pt print using the Printing Exposure determined above.

 

Using this Pt/Pd print, find the position on the gradient at which there is discernible difference between the gradient and the blank substrate.  The step, at this position, is the Maximum Black Threshold.

 

Measure the distance from one end of the gradient.

 

 

Using Photoshop's Dropper Tool, find the step in the gradient which corresponds to this position.  Set dropper to the position and read Magenta and Yellow values.  These are the Maximum Black Threshold values.  This relates to the minimum amount of ink necessary to properly print the built negatives.  Any amount of ink density less than this value will not contribute to tonal separation in the print.  A threshold placed too low will cause lower shadow values to merge into Maximum Black and also result is a loss of the total number of tones available.   A threshold placed too high will result in a loss or lessening of the Maximum Black available in the print.  Keep in mind that all inks do not transmit identically and perhaps not even linearly.

The Maximum Black Threshold, for this example, is achieved with color values of 38% Magenta and 42% Yellow.
 

The Maximum Black Threshold is applied in the Base Curve Calibration (below).

Figure 10:  Comparison of the Pt/Pd print of the gradient with Maximum Black to determine the
                 Maximum Black Threshold.  The Maximum Black Threshold is measured, in this case to
                 be 7.60 inches from the left edge (red indicator) of the Maximum White final gradient.
                 The bottom of the figure is a copy of the top with levels adjusted so as to better discern
                  the Maximum Black Threshold point.

Figure 11:  The values of the Maximum Black step are determined using Photoshop's Dropper Tool
                 with the Color Mixed gradient.  The 7.60 inch position (red indicator) of the Maximum
                 White final gradient has color values of 38% Magenta and 42% Yellow.  For this
                 example, these color settings on the Base Negative will provide the Maximum Black
                 Threshold in the Pt/Pd print.

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Base Curve Calibration:
This produces a standard curve to be applied to every Base Negative.  The purpose is to set the Maximum Black Threshold without losing the Maximum Black and provide the desired shadow detail.  There are three ways to accomplish this.   This method guarantees not losing the Maximum Black in the print.

The selection of the value to place at the Maximum Black Threshold is an important choice.  This value along with the selected Maximum Black Threshold are a personal preference of each photographer.  Once selected and maintained constant, they will provide a consistent calibration.    One should consider a value which is low but should also consider that better separation will come from values denser than the toe of the film used for the original negative.  The placement of a Maximum Black Threshold at a certain density value of the film will influence how that film is used to store the image information.  Remember that any densities less than the Maximum Black Threshold are merged with Maximum Black.  For a print tone to be lighter than Maximum Black, the corresponding original negative portion must receive enough exposure to produce a density above the Maximum Black Threshold.

The following are the three options to generate the calibrated Base Curve.
OPTION A:  (using Color Mixed gradient)
OPTION B:  (using an original negative)  recommended
OPTION C:  (using a 21-step original)

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OPTION A:  (using Color Mixed gradient)

This option is straight forward and the easiest and assumes that perfect, optimized original negatives will be used.

Begin with the Photoshop file of the final gradient from the Maximum White Calibration.

 

In Photoshop, Image, Adjust, Curves;

For CMYK, leave as straight 1:1 line.

 

In Cyan and Black channels, change all output to 0.

 

In Magenta and Yellow channels, enter a curve such that:

Leave 0 and 100% points as they are.

 

Enter the Magenta and Yellow values of the Maximum Black Threshold as the output values for the input values of 5%.

 

Add two points above the Maximum Black Value so that the curve above this value is forced, as much as practical, into a straight line.

This will provide for discernible shadow tones while maintaining the Maximum Black, at a minimum expense of the 256 data steps available.  The input value of 5% is used in order to work with a manageable curve.  Input values less than 5% may require several more points to keep a straight line and may not provide enough opportunity for Maximum Black to appear in the print.
 

Apply the curve after saving the curve information;

change to RGB, 8-bit;

 

check to make sure the entire image is within gamut (using View, Gamut Warning and View, Preview, Cyan);

NOTE:  If the image is out of gamut, the Color Mix should be reselected and
              all calibrations repeated except for the Printing Exposure.
 

Print the file.

 

Make a Pt/Pd print of this gradient stacked with two blank substrates.

 

Evaluate the Pt/Pd print.

The steps of the printed gradient should all be discernibly lighter than Maximum black except for the densest end step which should be Maximum Black.
 

Adjust the Base Curve as needed to change any base values, reprint, and reevaluate.

 

Save the final Base Curve as the standard Base Curve to apply to all Base Negatives.

Figure 12a:  Color Mixed gradient.  The red mark identifies the Maximum Black Threshold.

Figure 12b:  Color Mixed gradient with Base Curve applied.  The red mark identifies the Maximum Black
                   Threshold.

Click Here to view the Base Negatives and Pt/Pd prints comparing the three Base Curve Options.
 

Back to Options

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OPTION B:  (using an original negative)  recommended

This option is a little more difficult than Option A and customizes the curve to an original negative.  The original negative should be typical of other original negatives to be used, as the Base Curve produced will be customized for this original negative only.

Follow the procedure,  through Channel Mixing, to make only the digital Base Negative using an original negative typical of others to be used.  As a standard use a full range original negative that has been optimized for the scanner.  (The High and Upper Negatives are not needed at this time.)

 

In Photoshop, Image, Adjust, Curves;

For CMYK, leave as straight 1:1 line;

 

In Cyan and Black channels, change all output to 0;

 

In Magenta and Yellow channels, enter a curve such that:

Leave 0 and 100% points as they are.

 

The lowest density of the original negative that will print just discernibly lighter than black should have an output value of the Maximum Black Threshold, Magenta and Yellow components.  Use the dropper to select the portion of image to identify the input values and their position on curve, then enter the Magenta and Yellow output values for that curve input.  This requires a decision to select the values of the original negative to be set to the Maximum Black Threshold.  Keep in mind that the decision at this point is to generate a standard condition to be applied to all similar originals; other decisions can be made later during creative control.

 

Add two points above the Maximum Black Value so that the curve above this value is forced, as much as practical, into a straight line.

This will provide for discernible shadow tones while maintaining the Maximum Black, but likely at the expense of several of the 256 data steps available.  In comparing Figure 14a with 14b, it is observed that the selection of the density to place at the Maximum Black Threshold will have some basic results.

• The lesser the original negative density chosen for Maximum Black Threshold, the lower the local contrast of the base values will be in the print.  Note that the contrast of the base may also be changed by selecting a different base/high split during scanning, however this split may also affect (or trade off for) contrast in the high and upper areas.
• The higher the original negative density chosen for Maximum Black Threshold, the more information of the original negative and the more number of tones in the final print will be lost.

Apply the curve after saving the curve information;

change to RGB, 8-bit;

 

check to make sure the entire image is within gamut (using View, Gamut Warning and View, Preview, Cyan);

NOTE:  If the image is out of gamut, the Color Mix should be reselected and
             all calibrations repeated except for the Printing Exposure.
 

Print the file.

 

Make a Pt/Pd print of the Base Negative stacked with two blank substrates.

 

Evaluate the Pt/Pd print.

Any potion of the print to be discernibly lighter than Maximum Black must be placed at or above the Maximum Black Threshold.
 

Adjust the Base Curve as needed to change any base values, reprint, and reevaluate.

 

Save the final Base Curve as the standard Base Curve to apply to all Base Negatives for similar original negatives.

Click Here to view Pt/Pd prints comparing the three Base Curve Options.

Back to Options

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OPTION C:  (using a 21-step original)
This option is a good way to investigate how the steps may be manipulated or for comparing original negatives of various theoretical dynamic ranges.  However, it is only useful for establishing a Base Curve based on a theoretical original and is the most difficult of the options.

Use a 21-step in place of the original negative.

 

Make a Base Negative following the procedure stopping after Color Mixing.

 

Save this 21-step Base Negative.

 

Change to RGB, 8-bit, and Print.

 

Make a Pt/Pd print of the Base Negative stacked with two blank substrates and the 21-step.

 

Evaluate the Pt/Pd print.

The lower density steps of the base tone negative should be identical to the respective steps of the 21-step with step 2 slightly discernible from step 1 (Maximum Black)
 

Calculate or guess a factor to bring each Base Negative step to match the 21-step in the print.  Only do this for the lower density steps.  Only an approximation is needed at this point.

 

In Photoshop, Open the Color Mixed Base Negative,  and use the curve adjustment (Image, Adjust, Curves) as follows:

For CMYK, leave as straight 1:1 line.

 

In Cyan and Black channels, change all output to 0.

 

In Magenta and Yellow channels, enter a curve such that:

Leave 0 and 100% points as they are.

 

Use the dropper to select steps of the 21-step to identify position on curve, then enter the Magenta and Yellow output values for that curve input  that was assumed above to produce identical values when printed again with the 21-step.

apply the curve after saving the curve information;

 

change to RGB, 8-bit;

 

check to make sure the entire image is within gamut (using View, Gamut Warning and View, Preview, Cyan);

NOTE:  If the image is out of gamut, the Color Mix should be
              reselected and all calibrations repeated except for the
              Printing Exposure.
 

Print the file.

 

Make a Pt/Pd print of the Base Negative stacked with two blank substrates and the 21-step.

 

Evaluate the Pt/Pd print.

 

Repeat adjustments of the curve until the print shows no difference between the digital Base Negative and the 21-step for the darker values only.  Do not consider how the negatives compare, only the Pt/Pd prints.

 

When identical, save as the 21-Step Base Curve.  The 21-Step Base Curve may be used as the Base Curve, if it is assumed that the film and processing used for the original negative respond identical to the 21-step.  With the 21-step, one has an entire set of fixed density steps to investigate variations throughout the entire digital negative procedure.  High and Upper tones can be investigated as well.  For many investigations, it is  simple to compare tone steps.

Figure 15a: 21-step after Color Mixing Figure 15b:  21-step after setting step 2 to the values of the Maximum Black Threshold.

Click Here to view Pt/Pd prints comparing the three Base Curve Options.

Back to Options

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