Following is a relatively simple three step method for making digital negatives. With some of the more forgiving processes like gum and casein, only the first two steps may be necessary. The best transparency film substrates are made by Arista, Ink Press, or Pictorico; have some on hand. Also, keep or convert the image to 16 bit depth and Adobe RGB or its grayscale equivalent, gamma 2. The second step in making a digital negative is to adjust the overall contrast of the negative to match the contrast range of the emulsion. For example, a palladium emulsion requires a negative with rather high contrast more ink.
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Following is a relatively simple three step method for making digital negatives. With some of the more forgiving processes like gum and casein, only the first two steps may be necessary.
The best transparency film substrates are made by Arista, Ink Press, or Pictorico; have some on hand. Also, keep or convert the image to 16 bit depth and Adobe RGB or its grayscale equivalent, gamma 2. The second step in making a digital negative is to adjust the overall contrast of the negative to match the contrast range of the emulsion. For example, a palladium emulsion requires a negative with rather high contrast more ink. A gum emulsion requires a negative with fairly low contrast less ink.
The way this adjustment is done is by controlling the maximum amount of ink the printer lays down. Its default setting is 0 and we will leave it at that setting. The Default setting for the Color Density slider is 0 and this yields a relatively low contrast negative suitable for gum or cyanotype. Here is the workflow to determine the correct negative contrast to match the photo process.
Download the free Step Tablet image file at alternativephotography. Open the file in Photoshop. An image of this step tablet is shown in Figure A.
Flipping the image ensures that left and right handedness will remain correct when the ink side of the negative is placed against the emulsion side of the paper during print exposure.
The following instructions are specifically for a Mac computer running Photoshop CS6 with an Epson printer. Figure B. Printer setup 1. The dialog window that will open is shown in Figure B. In the dialog box:. These varying contrasts will probably cover the entire range needed for most photo processes. When calibrating a new process, print a few and quickly determine which contrast setting will be necessary. When using Matte Black ink the Color Density slider is no longer needed. The entire range of contrasts needed for most photo processes can be obtained by changing the Max OD slider in the Advanced Black and White dialog from — 12 low contrast to 0 very high contrast.
Both Photo Black and Matte Black ink will produce good negatives. There is the option to use either one in case switching ink types is not desired. If making negatives for gum, casein, or cyanotype, use Photo Black ink and leave both sliders at their default positions. This print is then measured to find out how far off the mid-tones may be, and with this information a correction curve is constructed to bring the midtones back into perfect linearity.
Once constructed, this correction curve will be applied to the positive image file. Scan the tablet print using a flatbed scanner set to Reflectance Mode. Figure F. Scanner setup 2. Next, click on the Frame tab Figure F. Now go up and hit the histogram button at the top third button from the left. This will open up a histogram of the step tablet prescan Figure G.
Move the shadow and highlight sliders so they are just outside of all the pixels the dark stuff. Make sure the middle slider remains at 0. This will ensure that the scanner records all the information seen by the photo receptors and does not clip either the shadows or the highlights. Now go back to the main dialog box and hit Scan. The scanned image of the tablet print should open in Photoshop.
Blurring averages small irregularities on the scan and makes for more accurate readings. A histogram will appear with a dark slider and a light slider on either end. Hold down the Option key while grabbing the dark slider with the mouse. The entire screen will turn white.
Use the mouse to drag the dark slider to the right. Eventually black patches will appear on the screen.
These patches represent all of the pure black pixels in the image. Then stop. Hold down the Option key, use the mouse to grab the light slider. The entire screen will go black. As the slider moves to the left pure white patches will appear. These represent areas of the tablet image that have gone pure white. Move the light slider over until the area under the opaque plastic turns pure white and stop.
At this point the black and white regions of the step tablet image have been set to pure black and pure white, respectively, and now the tonal values of the other patches on the tablet will be measured. In Photoshop, go to the Windows menu, scroll down, and click on Info. The Info palette will open. In the upper right corner click on a small stack of lines that open the Panel Options window. For the First Color Readout select Grayscale. Close Panel Options but leave the Info Palette open.
Figure H. Take a sheet of paper and write two column headings on it, Input and Output. Values in the Input column will be taken from the numbers written on individual steps of the step tablet. Values in the Output column will be numbers read from the adjusted scan image of the step tablet print, measured with the Eyedropper tool.
If the contrast selected via the Color Density slider for the step tablet negative is nearly correct the first number pair may read Input 0, Output 1.
When done there will be two columns of paired numbers that will look something like Figure H. These number pairs describe a curve that shows how the image goes from pure white to pure black. On the original step tablet file Input equaled Output which means the midtones are linear.
On the scanned step tablet print Input will almost never be the same as Output since most photo emulsions respond to UV light in a non-linear, S-shaped fashion. Go to the top of the table, cross out Input and relabel it Output this operation is shown in Figure H. Likewise, cross out Output and relabel it Input. These are the number pairs needed to construct the correction curve. Figure I. Now, go up to the diagonal line in the Curves box and click anywhere on the line to place an active point this is shown in Figure I.
When this is done two more boxes will appear, labeled Input and Output. The active point will move to the correct position. Now add another active point, above the first point, and type in the next number pair. And so forth until all points for the entire correction curve have been added. Note: Photoshop only allows 16 points on the curve, so choose points where they really seem needed to define the curve in the middle not so many points are needed.
Remember that the real correction curve never dips down it will always ascend and will not have jagged dips and rises. It is quite acceptable to look at the finished curve and manually correct it to a smooth, reasonable curve.
Once the curve is constructed, click on the stacked lines in the upper right corner and choose Save Preset. Name the curve and choose a place to save it. A good suggestion is to make one folder to house all curves. Final notes to this 3-step system It is not necessary to go through all three steps every time. Step 1 is necessary to establish a Basic Exposure Time. It is almost always necessary to go through Step 2 and adjust the contrast of the image.
Step 3 may not be needed. Try it and see. Christina Z. Anderson is an Associate Professor of Photography at Montana State University, Bozeman, where she specializes in alternative and experimental process photography. Ron Reeder lives on Mercer Island, Washington. He retired in and began a second career in photography. He has written two books and several articles on digital negatives.
He prefers processes like palladium, gum bichromate and albumen. Could someone tell me whether you can make good correction curves with the scanner in your higher end multifunction ink jet printer like an Epson or Canon?
I used this method before with a good dedicated scanner used for film scans for albumen prints with great success. Any 1st or 2nd hand actual experience out there? Can anyone tell me if you should use grey inks on high-end inkjet printers, or should you only use black and white? I was not sure whether all of the inks on my Canon Pro-1 would absorb the appropriate wavelengths of UV for Pt and Pd printing.
This is a page pdf description of that workflow. This file is an image file that is useful in calculating the screen exposure time for polymer plates. This is a cobbled-together stepwedge also called a target by some that is used in polymer plate calibration. This is a downloadable template file that assists in making even screen exposure strips on an A6 plate during the calibration process for polymer photogravure.
6 Questions with Precision Digital Negatives Developer Mark Nelson
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Digital Negatives for palladium and other alternative processes