How I make my Image Stack for Digital Negatives…
This post is about how I create my Digital Negatives for printing in Van Dyke Brown. Before I get into the meat of the subject I need to tell you that I am a follower of Peter Mrhar’s gradient maps for creating my negatives rather than using curves. The maps will allow you to create a much more controlled negative without the issues normally seen in curves like wild spikes and twists which can really mess up your image. Peter has written a book on the subject called Easy Digital Negatives which can be purchased on Amazon for a small fee. The entire book leads up to the last chapter where he gives you an automated script that plugs into Photoshop that will create the gradient map. Read the entire book first to understand how to develop a exposure test strip and a 245 step print that his script need in order to build the map.
The basic recipe that Peter gives is:
- Create a exposure test strip to get the correct exposure under your UV lights for perfectly exposed dark tones (black/Brown). You do this with a piece of sensitized paper with a strip of un printed negative material covering 1/2 of the paper. You then place a total UV blocking material leaving 1 inch of uncovered space, and expose for 1 min. Then move the UV blocking material to uncover another inch of open paper/film for another min. Repeat this procedure for about 10 min to create your test chart. Annotate each exposure with pencil on the paper prior to developing to know what the exposure time was for each movement of the blocking material. Process and completely dry. Where the darkest tone that was under the unprinted negative material matches the darkest tone next to it on the paper only side you get your max exposure time. This then becomes your base exposure for the paper/emulsion comes from. You will need to do any paper treatments to your paper first like acid washing or applying Fumed Alumina.
Now print your 256 step chart that Peter provides on a piece of paper treated the same as in step 1, with a UV blocking color which you will learn about below. Process and dry. Scan the resulting image according to Peter’s instructions and feed it to his script in Photoshop and it will pop out a Gradient Map for you to place in your image stack (example below).
That is all there is to it to create your gradient map (his script will also create a curve if you so desire).
Ok, lets talk about how you put together your file to create your digital negative once your have your gradient map in hand! Below is a copy of my adjustment layers in my digital negative file.
Starting at the bottom and working up, take a look at each layer:
- Background, default layer in every PS file.
- White Background, if you select this the non image area of your negative will print black (green) and leave the emulsion unexposed and white.
- Transparent Background, basically the same as layer 2. I have this here so that I can select it and be able to read my text layer above on the negative.
- Black Background, if you select this layer then you will get a negative with the non image area printing white which will force expose the paper black.
- 256 step tablet. You can select this layer to print a test chart.
- Picture Goes Here. Place your image to be printed above this layer.
- Picture, REMEMBER even though we are printing a B&W image it MUST be in RGB mode because we are going to print the negative in COLOR to have a UV blocking layer on the top of the stack!
- Text layer with data to be printed on the paper but separated from the image. This is the bottom of a grouped set of layers that are all selected by simply selecting the group name, read on…
- Gradient Map for Lana Paper, acid washed and exposed for 2.5 min. This is the meat of the layer stack. This one layer will correct your MID TONES while the 2.5min exposure will correct for the dark tones. This layer is what make your negative work.
- Lana paper group name. Select this and the next 2 will automatically be selected. I have expanded them so that you can see them here for explanation.
- Group of 3 layers for Stonehenge papers with the same basic steps as 8, 9 & 10 with the only difference being a GRADIENT MAP created for Stonehenge paper rather than Lana paper! you can have groups for each of your papers used in the stack and simply check the boxes you need for the paper you are going to print on!
- Invert, you MUST click on this prior to printing the create your negative image, switching your blacks & whites.
- Red UV blocking color, click to choose, be careful to not select both Red and Green.
- Green UV blocking color, click to choose, be careful not to select both Green and Red.
- Select ONE and ONLY ONE gradient map group or your picture will not print properly!!
- Select ONE and ONLY ONE color UV blocking color or you picture will not print properly!!
Let’s talk a little about the UV blocking colors. It seem a little strange to use a COLOR layer when printing B&W but you need to realize that some colors are better than B&W for controlling your UV exposures! I have 2 color layers included in my image stack but there can be many others depending upon your printer, ink set and choice in negative film. For my system (Epson 7900 24 inch printer using the Image Print V9 RIP) I have found that the Green layer works much better. I am going to show you the difference below between using a B&W negative vs. the GREEN negative. Pay close attention to the density of the grasses next to the sky in both prints.
First using a B&W negative with the same gradient map…
As you can see the density of the negative especially in the grasses looks great, but when you look at the output print you can see that the grasses all turn white at the horizon and get lost!
Now let’s take a look at the negative with the GREEN UV blocking layer…
The first thing that you should notice is that the density of both the sky and the grass seems much less dense but when you look at the output print the difference is amazing!
The grasses are now full of texture and you do not loose any detail at the horizon. The exposure on both images are the same thus you have the same amount of dark areas of shade and in the tree, but the mid tones now are full of greater details. This was simply achieved by adding the color UV blocking layer.
As I talk about these technical details they may seem simple, but it did take a while for me to master them in all of their glory. The image used as an example for you is not yet to my liking. The sky is a little too dark and the shadows are too black. I have just this week created a new negative with corrections for those specific areas and will be printing this image again tomorrow!
Nothing comes easy with alternative printing. Our printing lives are full of trial and error, but once we master the basics of the digital negative the trial and error period will drop down considerably.
You can download a copy of my PSD negative stack files both here in my download link on the bottom of the right hand menu and on Facebook in the Van Dyke Brown Printing group or in the Digital Negatives for Contact Printing group. There is a download file button on the top of each group page that will take you to these files.
I hope that this has been helpful for you. If you have any questions on this process please leave a comment here or join the FB groups above and you will find a great group of people on each group who can and will assist you in your process!