How to improve quality of ICC profile for proofing purpose

Whenever high accuracy is expected high quality icc profile is required. Several rules can noticeable helps to built such profile better.

1. Printer Check List

1. Print Nozzle test to ensure no nozzles are clogged, if nozzles are clogged- clean until all nozzles are clear
2. Ensure that head alignment is correct
3. Ensure all settings of the printer and RIP software are correct and standard- then document and save these settings (profile will ony work for these settings)
4. Ensure all inks are valid, (e.g. the inks you will be using for the future, and the inks are not expired)
5. Ensure the substrate is your standard substrate that you will be using in the future to simulate your "Reference Printing Condition." Ideally you should use the best Match function in ChromaChecker Substrate Inspector to ensure your proofing substrate is within your E-Factor expectation for matching your targeted reference print condition that you are wanting to simulate. Ideally it is better to match the actual color of the substate you are simulating with your proofing substrate versus having the RIP add a dot simulation. A dot simulation often will match in a light booth, but will exhibit bad match in any other lighting condition.

An example of printer utility software for checking nozzles. The same software enables head alignment testing.

2. Prepare your instrument

1. Inspect your instrument. Clean calibration white plaque and optical path.
2. Be sure that ambient conditions are good - temperature for example has a big influence on results.
3. Use Instrument Inspector to evaluate if measuring device is in good working condition.
4. Make some initial measurements just to warm-up the instrument.

3. Printer Linearization

Linearize your printer if possible - consult RIP's user guide for details. If already linearized re-linearize it.

4. Qualify your Proofer Intra Page (spatial uniformity) conformance 

1. Print the ChromaChecker VI816 (11x17) target multiple times if larger print area within imaging area. 
2. Measure all targets and save as separate files defining the location of the imaging area as part of the name
3. Build a Qualification Track in Print Inspector for assessing the Proofers Spatial Uniformity.
4. Import the measured targets, and group. If E-Factor of Intra Page uniformity is higher than your targeted accuracy to your Reference Print Condition, repair printer before proceeding to next step.
5. Measure at least one of the VI816 targets twice, once after your normal delay to measure, and then measure the same target 3-4 hours later and name it in order to identify the later measurement condition. Use Print Inspector to Group the two measurements of the same target and ensure the variation between the two measurements is less than 20% of your desired E-Factor. If it is higher, you should continue measuring the same target until the difference is less than 20% of your desired E-Factor and remember this dry back time period for all future measurements including your profile target.

5. Qualify the dry back of your ink and substrate

Inkjet prints need drying time depending upon the substrate. A chemical reaction occurs between the ink and the coating in the substrate, ensure your print condition has stabilized before you measure the target. If unsure: 

1. Measure at least one of the VI816 targets twice, once after your normal delay to measure, and then measure the same target 2 hours later and name it in order to identify the later measurement condition. Use Print Inspector to Group the two measurements of the same target and ensure the variation between the two measurements is less than 20% of your desired E-Factor. If it is higher, you should continue measuring the same target until the difference is less than 20% of your desired E-Factor and remember this dry back time period for all future measurements including your profile target.

6. Define Profile test chart.

1. Use as many patches as possible. For high precision proofers 6000 patches can ensure noticeably better accuracy than 2000 patches.
2. Adjust size of the patch in scanning direction. Most instruments in scanning mode meassure each patch multiple times then calculates an average. The longer the patch size - the more times it is sampled and the more accurate the measurement. When using manual scanning measurement devices (e.g. i1 Pro) scanning at a slower speed will increase accuracy since each patch will be measured more times. 
3. For better patch recognition/accuracy, it is recommended to scramble patches as most instruments recognize them by contrast analysis.

7. Capturing data

1. When using manual scanning measurement devices (e.g. i1 Pro) scanning at a slower speed will increase accuracy since each patch will be measured more times. Scanning devices should be set up for accuracy not for speed (e.g. Barbieri  LFP).  Measure in a consistent speed and orientation. 
2. Some instruments have built-in an averaging option (e.g.  i1iO, Barbieri LFP) - use it whenever is possible.
3. If possible scan multiple test charts several times and average the data.

8. Profile creation

1. When profiling increase "quality setting" and reduce emphasis on smoothness
2. If building a Proofer profile, set the B to A table to the largest available size - that determines size of the table.
3. Use 16-bit granularity
4. If possible include CxF data into profile for future access to the measurement data and extra flexibility
5. Analyze and compare profile after creation - perform a simulated conversion with your target color space to ensure the profile will support your E-Factor goals.  

An example how to set profile parameters  (i1 profiler, RGB Printer profiling)

9. Guidelines for CMYK Printer specific settings

1. Total ink coverage, set based on the Linearization settings that were determined during total ink limit step.
2. Black Generation- be careful, these settings can greatly influence the quality of the printed result. Research normal settings for your output device.
3. Lighting Settings- Ideally use D50, unless you are aiming for a non-standard illuminant
4. Perceptual RI settings- Leave as default unless you know what you are doing.

10. ICC profile accuracy judgment

Print IT-8 test form, measure it and compare reference data to measured. Make a statistical analysis of measurements. The most important values are:

1. Maximum ∆E for all patches
2. Maximum ∆E for 95% patches
3. Average ∆Efor all patches
4. Average ∆E for 95% patches
5. Standard deviation for all patches
6. Standard deviation for 95% patches
7. Maximum ∆Ch for all neutrals
8. Average ∆Ch for all neutrals

11. Visual evaluation

Print Test form for visual evaluation. Use qualified (Use Lighting Inspector to qualify your booth) D50 Viewing booth to compare with master proof.

Focus on:

1. Substrate's color
2. Highlights and shadows in both color and B&W areas
3. Tonal ramp smoothness
4. Grey neutrality

Why reduce the optimization of data (smoothness)?

Data optimization (smoothness) is good for high-speed production devices with some natural variation- e.g. offset presses. While devices that are very consistent (not as much natural variation) like inkjet proofing devices, turning on smoothness will reduce profile accuracy, which you do not want. The more consistent and stable the device the more you do NOT want to use smoothness in the profile creation software. Below a comparison made between two profiles created from the same measurement file (CxF file). 

Solid shape (optimized profile) is smooth , but unoptimized  (red wireframe) is not.

 In real world data measured from inkjet prints are not smooth. 
The maximum ∆E for presented example was 0.2 ∆E comparing (smoothness parameter in i1 Profiler set to 30 and 10)