CRT:CRT Color Calibration Guide

This guide only applies to NTSC sets.

This page details how to calibrate the color on your CRT set using the open source HCFR software. HCFR stands for Home Cinema-FR, a French forum that made an open source colorimeter and software.

Requirements

• A good colorimeter:
  • ColorMunki Display
  • X-Rite i1 Display
  • X-Rite i1 DisplayPro
  • ColorHug (open source)
  • ColorHug 2 (open source)
  • HCFR Colorimeter (open source)
  • Any colorimeter listed here
  • It's recommended to avoid Spyder products, as the colorimeters themselves seem to drift after a few years and require recalibration.
• A PC video card or downscaler and cables capable of outputting 480i to your CRT set. Use the best option available to you (i.e. HDMI > RGBS > s-video > composite). Do not calibrate using 240p as it will be incorrect, even if you are only using the set for 240p content.
• A PC capable of running HCFR for Windows

HCFR Setup

1. Install HCFR for Windows.
2. Under the Information section, select "CIE Diagram" from the drop-down menu.
3. Click the "Refs" button on the right-hand side.
   • On the Standard drop-down menu, select SDTV - REC 601 (NTSC).
   • If your CRT is set to 6500K (the "warm" white-point setting), choose D65. If your CRT is set to the 9300K (the "cool" white-point setting), choose D90. Most professional sets have a switch, possibly in the back. Consumer CRTs are more likely to be set to 9300K, but may have an option in the menu to change between the two.
   • Select the "Display Gamma (power law)" radio button.
   • Look through your CRT set's service manual and take note if there is any specified calibration targets. For instance, it might say that "if at a gamma setting of 2.4, 100 IRE is 100 nits, then 20 IRE should be at 2.7 nits" or some other specific values. If so, enter the specified gamma number under "Power Law Gamma" and click Apply.
     • If no specific values are provided in the manual, set gamma to 2.3 and your 100 IRE target will be 120 nits and your 20 IRE target will be 3 nits. This appears to be the values most Sony professional models are calibrated to.
4. Click the Advanced tab. Look at the service manual to determine when your CRT model was first produced. Use that to determine the Color Difference Formula to use under Refs > Advanced tab. Different Color Difference Formulas were established in 1976, 1994, 2000 - so choose the option previous to the year your monitor was produced (i.e. CIE94 for a monitor made in 1998). Click Apply and OK.
5. Click the edit button in the Generator section in the top-right of the window. Select your monitor on the target screen. Change "Image Area (%)" to 25 and click OK.

Calibrating Greyscale

First, you will calibrate greyscale to make sure the brightness and contrast are at the correct level for color calibration.

1. Mount the colorimeter in the center of your screen.
2. Click the "Measure gray scale" button, and look at the red/yellow/red results for DeltaE to see how well the grayscale is calibrated your set.
   • You are wanting a low (<2.0) DeltaE for every value. Anything below a value of 1.0 is not really visible by the naked eye.
   • Below 0.5 for all values isn't really obtainable for anything but later professional or broadcast monitors.
3. Click the "100" column header (% White) on the table to select 100 IRE and click the "Run or stop continuous measures". The screen will display a white image at 100% brightness. Change the contrast value on your CRT set until the "Y" value in the 100 IRE column matches the value the service manual specified for 100 IRE.
   • If your service manual did not specify a value, target 120 nits.
4. Click the "20" column header to select 20 IRE. Change brightness value to try and get "Y" value to try and match the value the service manual specified for 20 IRE.
   • If your service manual did not specify a value, target 3 nits.
5. Repeat the two above steps until you are as close as possible to your target values for 100 IRE and 20 IRE. You will likely need to repeat these steps quite a few times.

Calibrating Color

Next, you will calibrate red and blue color - repeatedly checking greyscale calibration as you go. If everything ends up perfect, the white triangle in the CIE diagram (current state) will match up with the black triangle (target state).

Click the "Measure primary and secondary colors" button to see how well the color is calibrated on your set.

• You are wanting a low (<2.0) DeltaE for every value. Anything below a value of 1.0 is not really visible by the naked eye.

You can subjectively view the color calibration by pressing Ctrl+0 through Ctrl+9.1

You generally can't change green values on CRT sets, so if green is far off-target in the CIE diagram, you will need to fix color purity either through menu options (for very high end sets) or through adjusting the rings on the yoke of the set. It may also be caused by a magnetic issue that can be fixed with an external degaussing.

First, you will target 20 IRE:

1. Select the 20 IRE table header once again. Take a look at the "Current Measure" table at the bottom half of the screen and note the R (red), G (green), and B (blue) values. The G value should be close to your "Y target" for 20 IRE.
2. Change the red cutoff setting in the service menu and try and get the R value to match the G value. As you adjust it, the B value may change.
3. Change the blue cutoff setting in the service menu and try and get the B value to match the G value. As you adjust it, the R value may change.
4. Repeat the two steps above until you find a balance where R and B are as close as possible to the G value.
5. Click the "Measure gray scale" button again, and look at the red/yellow/red results for DeltaE. You should see that the left half of the values are now better.

Next, you will target 100 IRE:

1. Select the 100 IRE table header once again. Take a look at the "Current Measure" table at the bottom half of the screen and note the R (red), G (green), and B (blue) values.
2. Change the red drive setting in the service menu and try and get the R value to match the G value. As you adjust it, the B value may change.
3. Change the blue drive setting in the service menu and try and get the B value to match the G value. As you adjust it, the R value may change.
4. Repeat the two steps above until you find a balance where R and B are as close as possible to the G value.
5. Click the "Measure gray scale" button again, and look at the red/yellow/red results for DeltaE. You should see that the right half of the values are now better.

Repeat each set of calibration steps above for 20 IRE and 100 IRE until both the RGB values at 20 IRE are equal AND the RGB values at 100 IRE are equal. Click the "Measure primary and secondary colors" button again to see how the color calibration looks now. You can subjectively view the color calibration by pressing Ctrl+0 through Ctrl+9.

At the top of the window, select Measures > "Full Tilt Boogie" to run all tests to see the most updated information.

Definitions

Term	Definition
White Point (D65, etc)
Rec601	The Color Space standard for NTSC Standard Definition Television (SDTV).
Rec709	The Color Space standard for NTSC High Definition Television (HDTV).
Nits	Brightness unit (candelabra per square meter?) representing how much light is being output for a certain area. This is the "Y" value in HCFR.
IRE	A unit representing the percentage of whiteness of a signal in a NTSC composite signal. Stands for "Institute of Radio Engineers". This is the header row in the main table in HCFR.
DeltaE	The difference between your current nits value (Y value) and the target nits value (Y target).
NTSC 3.58
Y value	Current nits value.
Y target	Calculated target nits value. At 100 IRE, this will match the current nits value observed.

Tips and Troubleshooting

• If on a 50% gray screen you are seeing spots that are discolored, try doing an external degauss.

Questions:

Calibrating PAL/SECAM? There's a Color Space Standard option for it.

When to use Rec709? (480p? 720p? 1080i? 1080p?)

How to read CIE diagram? Do you just want all colors to be in straight lines?