Relinearising Piezography Curves with a ColorMunki

Much of the discussion of how to measure the linearity of and relinearise Piezography curves is written for the i1 Photo measurement device.  A ColorMunki is a more affordable option, but its workflow is not well documented.  This how-to by Larry Beach, a regular on the IJM forums, fills that gap. Published here with permission.

This method uses the 21×4 random found in the C:\Program Files (x86)\QuadToneRIP\Eye-One directory (Applications>QuadToneRIP>Eye-One on OS-X) when QuadToneRip is installed. If you cut a 13×19 sheet in half, you have enough room to print a large enough patch to measure. Other 21×4 targets may be used, and may allow faster “strip measurement”.

1. Print the Step-21×4-random.tif

a. Cut a 13×19 sheet of your paper into 13×9.5.
b. Open QTR, open the Step-21×4-random.tif.
c. Select Custom size and enter 9.5×13.
d. Select your printer and appropriate Quad under the model.
e. Under Placement use 0.15 and 0.15; Under Scale check “To Fit”
f. Select the curve as the basis for relinearisation.
g. Make sure all other settings are correct for your paper and printer.
h. Print.

2. After sufficient dry time…

a. Open the ColorMunki Photo, and use Photo ColorPicker.
b. Select ColorMunki, move the dial to the calibrate position, then click on Calibrate.
c. If there are patches in the box below, click on Clear Measurements. This is not necessary, but saves confusion.
d. With the ColorMunki, click on each patch in turn.

i. begin at “Beg 30″
ii. 1st patch of the 2nd row
iii. 1st of the 3rd row
iv. 1st of the 4th row
v. Then repeat with the 2nd column (70).

Be sure to centre the ColorMunki carefully over each patch. This is a little time consuming, but not very difficult. Measuring in this order will give you an order that will cut and paste into Roy’s template directly.

e. When done, ensure you have 21 patches in the correct order.
f. Click on + Folder to create a folder for the paper you wish to relinearise.
g. Double click on the Untitled Folder and rename it appropriately.
h. With the new folder highlighted, click on + Palette.
i. Double click on Untitled Palette and rename it appropriately.
j. Click back on the ColorMunki resource, select all patches, then drag them to the new palette.
k. Click on File-> Export, Choose *.cxf, then choose an appropriate folder on your computer.
l. Close ColorPicker

3. Importing data into Excel

a. Download ColorMunki_XmlImport.zip from: http://cdn.northlight-images.co.uk/file-download-page-photography/ (or directly from http://cdn.northlight-images.co.uk/downloadable_2/ColorMunki_XmlImport.zip)
b. Click on the zip file, then on the XmlImport.xls file.
c. Once XmlImport is open, right click on the ColorName, click on the XML, then on Import.
d. Change Files of type to all files
e. Locate and click on the .cxf file you created from ColorPicker.
f. Save this file with a appropriate name.

4. Building .txt file for relinearising .quad file

a. From Excel, locate and open the template file QTR-21×4-random.txt. It is probably in the C:\Program Files (x86)\QuadToneRIP\Eye-One folder (Applications>QuadToneRIP>Eye-One on OS-X).
b. Rename this file to something logical for your data.
c. From the Excel file containing your Munki data, select and copy the data from columns B, C, and D (L, A, and B data).
d. Switch back to the template file and paste the data into columns D, E, and F.
e. Verify that the data is ordered correctly by selecting all the data, click Data, Sort, then by Column C. If the L values either increase or decrease evenly, your data is well ordered. If you have any L values that go higher or lower than they should (reversal), it will not relinearise.
f. Resort the data according to Column A ascending. (This is probably not necessary).
g. Save this file as a .txt using a logical name for the paper you are relinearising.

5. Relinearise

a. Open the folder that contains the QTR-Linearize-quad.exe (C:\Program Files (x86)\QuadToneRIP\Eye-One).
b. Select both the .txt file you made from your measured data, and the .quad file you are relinearising.
c. Drag both files onto the QTR-Linearize-quad.exe.
d. An -out.txt file should be created and can be used to troubleshoot problems if they occur.
e. A new .quad file should be made. If it is not made, it is possible that this method will not relinearise the .quad for the paper you are using.

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