Using Babelcolor Patch Tool or SpectraShop 4
This post describes how to measure color and grayscale patches on a variety of test charts, including Imatest SFRplus and eSFR ISO charts, the X-Rite Colorchecker, ISO-15729, ISO-14524, ChromaDuMonde CDM-28R, and many more, using a spectrophotometer and one of two software packages.
- Babelcolor PatchTool which works with reflective test charts
- Robin Myers SpectraShop 4 which works with both reflective and transmissive (backlit) test charts
Measurement results are stored in CGATS files, which can be used as reference files for grayscale and color chart analysis in Multicharts, Multitest, Colorcheck, Stepchart, and SFRplus. In many cases, custom reference files provide more accurate results than the default values.
In addition, Argyll CMS is a free, Open Source, command line-based package that can be used for a number of measurements, including illumination intensity and spectrum. See the Argyll CMS documentation for more details.
At Imatest we currently use the i1Basic Pro 2 (a good choice if you’re shopping for a new instrument; ). We’ll call it the i1Pro in the text below. It’s one of several instruments supported by Babelcolor PatchTool and Robin Myers SpectraShop 4 software. The i1Pro is primarily designed for reflective readings, but it can also be used to measure transmissive (backlit) charts.
- If you don’t have the original disk, Load the drivers and software from X-Rite. For our i1Pro we clicked on Software downloads (5 Items) (on this page), and loaded all relevant software. For the i1Basic Pro 2, go to this page.
- Install the drivers for your system and i1Diagnostics. Run i1Diagnostics to make sure your hardware is functioning properly.
- The other programs for the i1Pro are useful for purposes such as monitor calibration, but not directly relevant to chart calibration/patch measurement.
Read the description of PatchTool on the Babelcolor page, then download and install it. You’ll need to purchase it in order to run Patch-Reader (no luck with evaluation mode). Registration is straightforward (no special instructions needed).
- Open PatchTool. The window is very simple— not much to it.
- Click Tools, Patch-Reader… to open the Patch-Reader…
- Select the Chat type. Click Custom chart for rectangular grid charts (like the X-Rite Colorchecker), and select the correct number of rows and columns. The default is 4 rows, 6 columns (for the Colorchecker). Select 4 rows, 5 columns for SFRplus color and grayscale charts. Unconstrained measurements work perfectly well for rectangular grid charts and must be used for charts that don’t have a regular rectangular grid (like the ISO-15739, CDM-28R, etc.). The Patch-Reader window will look like this.
Initial Patch-Reader window (4 rows, 5 columns)
- Press Start. A window opens with the following message for calibrating the spectrophotometer. Follow instructions and press .
|REFLECTANCE CALIBRATION: Remove the AMBIENT DIFFUSER if installed. Place the i1Pro on its BASE (white tile). When ready, press the ‘Return’ or ‘Enter’ keys or close this message window.NOTE: This calibration may take several seconds!
- After you finish the calibration, and buttons appear on the lower-right of the Patch-Reader window.
- Place the i1Pro on the first patch of the chart and click the button on the side. This is equivalent to pressing (which should never be necessary).
- Now go through the patches one-by-one, by rows (for rectangular charts). For non-rectangular charts you’ll need to know the patch order, which is described below. For rectangular grid charts the Patch-Reader window will displays the location of the next patch to measure. Be sure to position the i1Pro carefully over the center of the patch and press it firmly against the target to minimize stray light. (Subdued room light doesn’t hurt.) (For a m row x n column chart, the order is Row 1-Col 1, Row 1-Col 2, … Row 1-Col m, Row 2-Col 1, etc.)
|A little inconsistencyAlthough you enter patches by rows (R1C1, R1C2, …, R1Cn, R2C1, … R2Cn, …) at Patch-Reader’s prompting, the patches in CGATS files (created using Custom chart: m rows x n columns) are stored by columns: (R1C1,R2C1, …, RmC1, R1C2, …, RmC2, …). This is NOT consistent with CSV files, which are stored by patch order, i.e., rows (R1C1, R2C2, …R1Cn, R2C1, … R2Cn, … for rectangular charts). Imatest recognizes the file type (CSV or CGATS) and interprets the patch order correctly (using the LGOROWLENGTH setting in CGATS files).|
- You can use the mouse to select a patch to measure, i.e., you can go back and re-measure if you have any doubts about measurement quality.
- When you have finished the Patch-Reader window will look like this. You should examine this image carefully to be sure it resembles the chart— all patches should look correct: You can still select patches to re-measure if necessary.
Patch-Reader window after all patches have been read
- Click , and the a window appears with the following options.
|Do youl want to Save these measurements?Click ‘Cancel’ to continue making measurements.
- When you click Imatest use, only the L*a*b* data field needs to be checked. ID (SAMPLE_ID; the numeric sequence) and Name (SAMPLE_NAME; The alpha column and numeric row, i.e., A1, …, A4, B1, …, F4) may be checked, but will be ignored by Imatest. XYZ and xyY may be checked, but will be ignored if L*a*b* is checked. (The order of precedence in reading data is L*a*b*, XYZ, then xyY.) , the following window appears. For typical
- The save file name should include the media type (matte, luster, …) and any other information needed to identify the chart.
PatchTool writes files in CGATS format (an industry standard best explained in the PatchTool Help PDF document). Imatest can read CGATS files starting with August 2013 3.10 builds. Here is an example:
CGATS.17 ORIGINATOR "BabelColor PatchTool, version 4.1.0 b321" LGOROWLENGTH 4 CREATED "2013-07-01" # Time: 1:25:46 PM INSTRUMENTATION "i1Pro" INSTRUMENT_SN "608994" MEASUREMENT_SOURCE "Illumination=D50 ObserverAngle=2 WhiteBase=Abs Filter=UVcut" ILLUMINATION_NAME "D50" OBSERVER_ANGLE "2" FILTER "UVcut" MEASUREMENT_CONDITION "M2" WEIGHTING_FUNCTION "ILLUMINANT, D50" WEIGHTING_FUNCTION "OBSERVER, 2 degree" KEYWORD "DEVCALSTD" DEVCALSTD "XRGA" # # THIS FILE CONTAINS REFLECTANCE MEASUREMENTS MADE WITH PatchTool Patch-Reader # # Chart_type: "Custom chart" # No_rows: 4 # No_columns: 5 # No_samples: 20 # NUMBER_OF_FIELDS 3 BEGIN_DATA_FORMAT LAB_L LAB_A LAB_B END_DATA_FORMAT NUMBER_OF_SETS 20 BEGIN_DATA 44.050 -4.479 -15.534 46.989 3.638 -16.591 38.129 6.395 6.321 52.539 -0.730 -3.700 40.766 32.354 14.498 42.772 -19.174 -21.994 57.309 12.668 12.012 53.507 1.771 3.460 47.533 -25.359 16.443 44.629 32.242 -6.113 61.667 -18.258 37.479 37.817 2.403 -27.741 33.075 4.416 -29.699 75.079 4.192 62.638 63.637 15.573 46.478 45.767 28.423 10.312 41.007 -8.057 10.701 59.762 -28.214 -1.841 55.213 23.810 34.126 33.661 10.341 -10.492 END_DATA
Download and purchase SpectraShop 4 using links at the bottom the product description page. Both Windows and Mac versions are available. The brief Tutorials are recommended. You should also download the full PDF manual and look at the FAQ, which has troubleshooting information. Open SpectraShop 4. Click on the Measure specimens box, which is the second from the left. (I’ve tried Create and edit charts and Measure chart without luck.)
Measure specimens is the second box from the left
This opens the Instrument Connection window, shown on the right. Select the spectrophotometer, click , select the Specimen Type (reflective, transmissive, etc.). Be sure the spectrophotometer is on its base (with white tile), then press .
Instrument Connection window, shown just before Calibration
|After Calibration is complete, the Measure Reflective Specimens page will open. None of the settings are critical, but we recommend
When you have finished making settings, press below. . Place the spectrophotometer sensor over the patch. If possible the room should be dimly lit to minimize light leakage. Take each reading by clicking the spectrophotometer button— waiting about two seconds for a beep indicating that the reading is complete. Patch order is described Take readings carefully. I haven’t (yet) found a convenient way to edit or redo erroneous readings.
Saving the reference file
I recommend saving results in two formats: the default SpectraShop 4 ss3 format (not interchangeable, but can be reopened in Spectrashop 4), which contains all results (including the spectrum), and CGATS with just the results used by Imatest. To save the SS3 file, click (in the window shown below) File, Save… or Save as… The procedure for saving Imatest-readable CGATS files is shown below.
Main SpectraShop 4 window showing Colorchecker results
To save the measurements in an Imatest-readable CGATS file, click File, Export… The window on the right opens. Select CGATS 1.7 ASCII as the Export Format. Spectrum should be unchecked and L*a*b* should be checked. XYZ and xyY may be checked if desired, but they will be ignored by Imatest if L*a*b* has been checked.
Spectrashop 4 Export window
Here are the results:
CGATS.17 ORIGINATOR "" CREATED "2013-08-28 16:43:55" INSTRUMENTATION "i1Pro" MEASUREMENT_GEOMETRY "45/0" MEASUREMENT_SOURCE "A" WEIGHTING_FUNCTION "OBSERVER,2 degree" WEIGHTING_FUNCTION "ILLUMINANT,A" NUMBER_OF_FIELDS 4 BEGIN_DATA_FORMAT SAMPLE_ID LAB_L LAB_A LAB_B END_DATA_FORMAT NUMBER_OF_SETS 24 BEGIN_DATA "Colorchecker-01" 39.80 14.43 17.09 "Untitled-02" 67.86 22.51 20.21 "Untitled-03" 48.51 -9.36 -23.27 "Untitled-04" 43.04 -10.81 20.67 "Untitled-05" 54.88 5.55 -24.67 "Untitled-06" 68.04 -32.15 -6.00 "Untitled-07" 66.70 34.88 63.83 "Untitled-08" 38.48 -0.44 -45.06 "Untitled-09" 56.15 47.12 25.25 "Untitled-10" 31.91 17.66 -16.69 "Untitled-11" 71.40 -16.98 50.80 "Untitled-12" 74.84 21.00 71.57 "Untitled-13" 27.04 0.66 -49.03 "Untitled-14" 52.88 -32.25 23.97 "Untitled-15" 47.07 55.90 37.55 "Untitled-16" 83.99 9.76 78.29 "Untitled-17" 55.75 47.38 -5.30 "Untitled-18" 47.53 -31.32 -35.23 "Untitled-19" 95.01 0.32 4.03 "Untitled-20" 80.78 -0.72 0.38 "Untitled-21" 66.36 -0.71 0.28 "Untitled-22" 49.81 -1.43 -0.39 "Untitled-23" 36.00 -0.85 -0.45 "Untitled-24" 20.92 -0.34 -0.53 END_DATA
Charts with a regular m x n rectangular grid have patches numbered in a sequence shown in the example below for the 4 row X 6 column X-Rite Colorchecker. Use this order in acquiring patch data.
Patch order for charts supported by Multicharts can be displayed by running Multicharts, selecting 3. Split Colors: Reference/Input (in Display), then checking the Numbers checkbox. Here are the patch numbers for the DSC Labs CDM-28R.
Multicharts result, showing patch numbers, for the ChromaDuMonde 28R.
|There are a few special cases, such as the Rezchecker (a tiny precision reflective chart for measuring color, tones, and MTF). The numbering follows the standard rectangular grid, but corner patches and patches used for slanted-edge MTF have L* = a* = b* = 0 in their reference file, and are omitted from color analysis. For the Rezchecker these include patches 1, 6, 8-11, 14-17, 37, and 42.||Rezchecker||Rezchecker numbering|
Some cases are not obvious, like the eSFR ISO color patches, which are supported by Multicharts, but usually run in eSFR ISO.
eSFR ISO color patches