Each gray scale area should be marked by "double-points" in CooRecorder, like 2:1, 2:2, 3:1, 3:2, 4:1, 4:2 etc. Because of the way CooRecorder works, the very first point has to be a single point not used for calibration information - this is valid at least when the calibration file is of "dendro data type" and not of "raw type". The "pair points" (.e.g. 3:1, 3:2) should all be placed on the border of an imaginary square so that each point is placed in the middle of opposite sides of the square which then surrounds the corresponding gray scale region.

The "binding" of a density value to a certain gray scale region is done by storing a (scaled) density value like "127" into the point label for each double point at its gray scale region.

With these points and point labels in place, you should save this as your "calibration file" e.g. as plexiladder.pos

Your selection of Data-type for the calibration file: When the gray scale regions are all laying on a line one after the other on the calibration target, the data-type of the calibration image when stored as a .pos file can very well be of type "Sorted data" like for a normal ring width coordinate file. Though if the regions are distributed e.g. like on a chessboard, then "Type of data" should be set to one of the Raw data types, otherwise CooRecorder will complain about "Erroneous order among points". In the case of raw type of datafile, the points will not be sorted in any order. Neither do you have to care about the order as CooRecorder will automatically sort the gray shades for data conversion in the right way.

To create the "calibration curve" which will be used for calibrations, you should now issue the command "CI-measurements /Create or load calibration curve" and then, within the window that pops up, "Calibration CURVES/Create(X-Ray) calibration curve from ladder image .pos file".

This command will lay out the measurement frames from which the gray scale values (shades) will be calculated. It will also check the consistency of the point-labels (describing known scaled density values for the various parts of the ladder) and create a "Calibration curve" as shown in the diagram above. This curve will be used to transform gray scale values into densities when you later create CI data (blue lb-button) from the various gray shades of the X-ray scanned image of a wooden sample. You should carefully inspect the calibration curve and how the the frames are laid out. If you find errors, make your updates, save the file and see that you create a new calibration curve as described above.

When the calibration curve looks correct, see that you save it (Calibration CURVES/Save calibration curve(s)). The calibration curve is now loaded and ready to be used. Though to have calibration actually turned ON, you have to see that the radiobutton for "Calibration ON" is checked, see in lower right corner above. After you have closed the "CI calibration curve" window, you should also close the calibration image file.

Next time you want to use this calibration curve, use the command CI-Measurements/Create or load calibration curve and then Calibration CURVES/Load calibration curve(s). And again, do not forget to set the Calibration ON radiobutton before closing this window.

Now, to create calibrated density data, open an image or an already existing .pos file for which you want to generate density data. Also see that you have a CI collector setup with a request to write data to a .wid file. To actually create the density data, click the blue lb button and check the positions of all the frames showing from where the data is generated. To save both your .pos file and the .wid-file(s) with density data use the command "File/Save CI measurement .wid file AND .pos file if unsaved"

An even more easy way to quickly generate and save data for all enabled CI collectors is to check "Run ALL enabled CI collectors (and save .wid files)?" and then click on OK for "Now also save CI data .wid files?" as shown above.

A scan of the calibration target (the "plexi ladder") should possibly be done every day after the X-ray scanner has been thoroughly warmed up. So if you need to often recalibrate your scans by again scanning the calibration target, you might get tired of reentering points and density data for your calibration image - which probably looks almost the same each time.

With the command "Open .pos file with ANOTHER image" you can replace the current image of a .pos file with another image. I.e. if your calibration images always look almost the same though the gray shades might differ a little, you might replace the old image of the .pos file with a new one. You then only have to check that the CooRecorder points are correctly placed and adjust if necessary and then save the file (possibly with a new name) and finally order the command CI-Measurements/Create or load calibration curve and then Calibration CURVES/Create (X-Ray) calibration curve from ladder image .pos file This simple replacement of the .pos file image with a new one, might facilitate your calibration work considerably.

You can easily check your XRay/Density calibration by doing a measurement over that same "ladder image" that you used to create the XRay/density calibration curve. In this case you set sort of ring border points in about the same way as when you measure ring widths on a wood sample.

So if we calculate a mean blue value for the whole spot and then convert it to a density value, we then get 319. But if we convert every pixel's blue value into a density value and then take the average value then we get 314! So this seems to be a matter of how we should calculate the density! As the calibration curve is quite steep at this point the resulting density value will depend heavily on small changes within the blue color.