Using a SpyderPrint to Read Calibration Target Prints for Digital Negatives

Introduction

For many years, I used an old-school X-rite 400 Reflection Densitometer to take readings of step-tablet prints, analog and digital, to calibrate negatives for Platinum/Palladium prints and other alternative photographic printing processes. Two or three years ago the densitometer suddenly stopped working. I had a DataColor Spyder3Studio SR kit that I had gotten to calibrate my monitor and printers for digital printing, but until that time I had never thought of it as a substitute for the densitometer.

About the SpyderPrint

The DataColor Spyder3Print is a spectrocolorimeter. It reads LAB color values, which mimics human eye-brain perception. In other words, it is designed to see color the way we do. A densitometer, on the other hand, measures light absorption on a logarithmic scale, which is why a graphically linear plot of Density values looks visually dark. A graph of a linearization based on the L* (Lightness) component of LAB actually looks visually correct.

The picture above shows the 3 components of the Spyder3Print – the spectro itself (front), the base (middle), and the guide (back). The USB cable is not shown. Personally, I don’t use the guide, preferring to make my readings freehand.

For our purposes, we don’t use the standard Wizard based procedure that the SpyderPrint software guides you through when making profiles for inkjet printing on paper. Rather, since we are reading the results of printing a negative, we will use the manual Measure function under the Tools menu. Unfortunately, the manual is a bit lacking on how to use these tools. These two paragraphs are from the manual and that’s all there is about them. A call to DataColor support just referred me to this as well.

Tools Calibrate function: This button launches a calibration window that allows both black and white tile calibrations. It is not necessary for standard use; the calibration function occuring in the Wizard interface is all that is needed. Calibration from the Tools menu is a for special testing and support purposes, or for calibration when using the Tools Measure function.

Tools Measure function: This button launches a measure window that allows measurements to be taken, and displays L*a*b* color values and Visual Density values of for each patch after it is read. If a log of measurements is desired, it can be named, and exported as Lab, Visual Density, or special QTR linearization and QTR CreateICC formats for use with QuadTone RIP®. Once the user completes the measurement set, the Done button stops the export process, and closes the Measure window.

Procedure

You skip all of the guided steps, but before you can access Measure on the tools menu you have to Calibrate.

1. Go to Tools>Calibrate (Command+K), make sure the Spyder is in it’s cradle and either push the button on the the Spyder or hit Return/Enter, then click OK.
   

   
2. Now you can go to Tools>Measure (Command+M). Here’s where it gets a little less than straightforward.
3. First you need to select (1) Open Export …. This opens a Finder window showing a deeply buried folder where SpyderPrint saves data. (The full path, in case you ever need to find it without going through the app, is [username]/Library/Preferenced/Datacolor/SpyderPrint/Data/Export.)
4. Then go back to the SpyderPrint window and select (2) Export to …, it opens with ExportedValues.txt as a filename – change this to something meaningful like 1430PiezoDN-Pd-Master.txt, and click OK.
5. Unless something else is checked, LAB is the default reading so you don’t actually have to select it here, but it’s ok to do so if you want. Just be sure nothing else is checked.
6. To make your readings, begin at the lightest patch, set the sensor in the middle of the patch and push the button on the sensor (or push Return/Enter on your keyboard). Read each patch in order from lightest to darkest, then click Done.
7. The readings are saved as a Tab Delimited Text file in the above referenced folder. There is one row for each reading in the format L A B. Note that there are 129 rows in total, most of which are note visible in the screenshot.
8. Open the file, select all (Command+A), copy to clipboard (Command+C), go to the Curve tab in the Smoother tool, right-click the top left cell of the green section, and select Paste. (Note: It is not necessary to select the entire range.) Make sure that the first and last L readings are in fact the lightest and darkest. Follow the instructions on the page.

 Note: The last step is shown here is for the PiezoDN method from InkjetMall. This particular method uses a 129-step test target. The spreadsheet tool illustrated here is called the CGATS Smoother. It smooths the raw data, correcting bumps and waves that are very likely to occur with any hand-coated process, and converts the data into the CGATS format which is then saved as a text file to be used with the QTR-Linearize-Quad and QTR-Create-ICC apps that are part of Roy Harrington’s QuadToneRIP. The SpyderPrint app has other QTR specific functions built in though I haven’t used them yet.

The process is similar for other methods which typically use 21- or 31-step targets which are much simpler to smooth manually. In most cases, at least for digital negatives, you will only need to use the L* column, especially if you are simply pasting it into a spreadsheet. Measurements can also be made in Density mode.