CRT:CRT Color Calibration Guide

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.

A massive guide for grayscale and color calibration can be found here.

A great video guide by Lex Locatelli for calibrating your CRT can be found here.

Requirements

• A good colorimeter. Some colorimeters use organic color filters which degrade over a few years. The following are non-organic ones that should not degrade:
  • X-Rite ColorMunki Display
  • X-Rite i1 Display
  • X-Rite i1 Display Pro (faster sampling)
  • X-Rite i1 Display Plus (supports >1000 nits for LCD/OLED)
  • Calibrite ColorChecker Display
  • Calibrite ColorChecker Display Pro
  • Calibrite ColorChecker Display Plus (supports >1000 nits for LCD/OLED)
  • ColorHug+ (open source)
  • ColorHug 2 (open source)
  • Any colorimeter listed here
  • It's recommended to avoid Spyder products, as the colorimeters use degrading organic filters.
• A console, PC video card, or downscaler and cables capable of outputting the desired resolution to your CRT set that you wish to calibrate for. In order of preference:
  • Extron VTG 400 or other pro signal generator is the best option.
  • Wii (YPbPr), Dreamcast (Composite), PS2 (YPbPr; also compatible with FreeCalRec601 disc)
  • Wii (RGB, composite), Dreamcast (RGB, S-Video), PS2 (composite, s-video, RGB) if you can't use the above options.
  • A VGA-capable ATI/Radeon videocard with CRT Emudriver software can output 480i.
  • Any standard DVD player (YPbPr or composite with FreeCalRec601 disc). This is the last resort, as DVD player video output quality is all over the place.
• Note that all calibration done will only apply to the selected input channel (RGB, YPbPr, s-video, composite, RF). If you want to calibrate all inputs for the set, you will need to run through this entire process for each input. If you wish to do this, consult your service manual to see if there is a preferred order. Likewise, if your set supports higher resolutions (480p, 720p, etc), the settings are stored separately for each resolution. Do not calibrate using 240p as it will be incorrect, even if you are only using the set for 240p content. If you wish to calibrate for 240p content, use 480i.
• A PC capable of running HCFR for Windows

HCFR Setup

1. Install HCFR for Windows and plug in your colorimeter.
2. In the toolbar, click New, select Automatic > Next, then select your sensor from the drop-down menu and click Finish. If another window opens up, select the drop-down menu for "Display Type" and choose "Refresh display".
3. Under the Information section in the bottom-right, select "CIE Diagram" from the drop-down menu.
4. Click the "Refs" button on the right-hand side.
   • On the Standard drop-down menu, select SDTV - REC 601 (NTSC) if you have a NTSC set or PAL/SECAM if you have a PAL/SECAM set.
   • Decide whether you want to calibrate to D65 (6500K, US or Europe standard) or D93 (9300K, Japan standard) whitepoint. This is a personal preference, and you may want to look up comparison images to decide which color temperature you like better.
     • If your CRT set has an on-screen display (OSD) you should be able to change between 6500K and 9300K in the menu. If this is the case, any settings you change will only apply to this temperature.
     • If your CRT set does not have an OSD, check the back of the CRT set for a physical switch to change between 6500K and 9300K. Otherwise, assume it is at 6500K and choose that
   • Check the "Override black" checkbox.
   • Check 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.
5. Click the Advanced tab. Look at your 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, CIE2000 for a monitor made in 2005). Click Apply and OK.

Backing up Settings

Before making any changes, it's recommended to write down or take pictures of the settings in the user menu and service menu that you are likely to change.

That includes:

• Contrast (also called "Picture" on consumer sets)
• Brightness
• Red, Green, and Blue gain (sometimes called "Drive")
• Red, Green, and Blue bias (sometimes called "cutoff" or "background")

Then change all values in the __user menu__ (not the service menu) to either all 0 or all the center value. If your CRT has brightness, contrast, or color knobs or buttons; reset them all to the middle position. Some PVMs have a reset button on the front to do this.

Environment Setup

1. Load up 240p Test Suite on your console and select the 100 IRE test pattern under Test Patterns > Color. It should display a white rectangle.
   • If using a Dreamcast, also press Y on the controller to set it to "714.3 mV IRE".
2. Attach the colorimeter in the center of the white rectangle, with the wire draping over the top of the CRT so it doesn't pull itself off.
3. Turn off the lights in your room. The darker the room, the better.

Obtaining a Baseline

First, you will get a baseline to see the data of how bad your CRT colors and how much you will improve it.

1. In HCFR, select the 10% column header and press the Measure Gray Scale button (trailing gray balls icon). It will ask to run gray scale measurements. Click Yes.
2. It will ask you to set your screen to 10 IRE. In 240p Test Suite, press left until it says "10 IRE".
3. Click OK and it will take a sample.
4. After each sample, follow the directions to change the test pattern until the entire chart is filled and the test concludes.

Look at the yellow/red results for Delta E to see how well the grayscale is calibrated your set. Your goal during this calibration is to achieve a low (<2.0) Delta E for every value. Anything below a value of 1.0 is not really visible by the naked eye, but the lower the better.

• Achieving below 0.5 for all Delta E values isn't really obtainable for anything but later professional or broadcast monitors.

Calibrating Greyscale

In order to calibrate color, you will first need to calibrate greyscale to make sure the brightness and contrast are at the correct level.

First, you will need to target 100 IRE:

1. Select the "100 IRE" test pattern (under Test Patterns > Color) in 240p Test Suite and ensure it is set to "100 IRE".
2. In HCFR, click the "100" column header on the table to select 100 IRE and click the Play button. It will continuously sample the screen.
3. Change the contrast value on your CRT set — in the service menu if it has one or through potentiometers on the CRT motherboard — until the "Y" value (brightness in nits) in the 100 IRE column is as close as possible to the value the service manual specified for 100 IRE.
   • If your service manual did not specify a value, target 120 nits. If you use the set exclusively in a dark room, target 100 nits.
4. Press the red X to stop sampling.

Next, you will need to target 20 IRE:

1. In 240p Test Suite, press left until it displays the "20 IRE" pattern.
2. In HCFR, click the "20" column header to select 20 IRE and click the Play button. It will continuously sample the screen.
3. Change the 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.

Repeat calibration for 100 IRE and 20 IRE multiple times to find the optimal balance for your set with both the 20 IRE and 100 IRE values as close to their respective target values as possible.

Calibrating Color

In the service menu of your CRT, you should see gain and bias (or cutoff/background) settings for two of the three colors. For most sets, Green is the reference color, thus you only have settings to adjust Red and Blue. If Red, Green, and Blue settings are all present, consult your service manual for which color is the reference color. For the purposes of this guide, it will be assumed that Green is the reference color, and therefore any settings related to Green should not be modified.

• Professional Ikegami brand monitors and some Sony consumer CRTs use red for their reference color.

First, you will adjust gain (may be called "drive" on your CRT):

1. Set 240p Test Suite to 80 IRE, select the 80 IRE table header in HCFR, and press Play. Note the "RGB Levels" in the bottom-left corner of the screen.
2. Look at the Red cylinder:
   • If it is a higher value than Green, turn Red gain down.
   • If it is a lower value than Green, turn Red gain up.
3. Look at the Blue cylinder:
   • If it is a higher value than Green, turn Blue gain down.
   • If it is a lower value than Green, turn Blue gain up.
4. Repeat the two steps above until you find a balance where Red and Blue are as close as possible to the Green value. The goal is to get the Delta E (dE) value to below 2.0.
5. Press the red X to stop sampling.

Next, you will adjust bias (may be called "cutoff" or "background" on your CRT):

1. Set 240p Test Suite to 20 IRE, select the 80 IRE table header in HCFR, and press Play. Note the "RGB Levels" in the bottom-left corner of the screen.
2. Look at the Red cylinder:
   • If it is a higher value than Green, turn Red bias down.
   • If it is a lower value than Green, turn Red bias up.
3. Look at the Blue cylinder:
   • If it is a higher value than Green, turn Blue bias down.
   • If it is a lower value than Green, turn Blue bias up.
4. Repeat the two steps above until you find a balance where Red and Blue are as close as possible to the Green value. The goal is to get the Delta E (dE) value to below 2.0.
5. Press the red X to stop sampling.

Repeat the process again for 80 IRE and 20 IRE until they reach a balance where both Delta E values are as low as possible. Ensure that you properly stop, change the test pattern, change the selected column, and press Play each time.

Finally, repeat the process for calibrating your brightness and contrast, as the color adjustments you made will have affected the Y values.

Analyzing Results

Follow the "Obtaining a Baseline" section again to get the new baseline. Hopefully all Delta E values are under 2.0 and you can now look at the CIE diagram.

If everything ends up perfect, the white triangle in the CIE diagram (current state) will be very close to the black triangle (target state).

Since you generally can't change settings related to the reference color (e.g. Green), 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.

Definitions

Term	Definition
White Point (D65, D93)	This is the temperature of color defined as pure white (100% white).
Rec601	The Color Space standard for NTSC Standard Definition Television (SDTV).
Rec709	The Color Space standard for NTSC High Definition Television (HDTV), 720p and higher progressive resolutions.
Nits	Brightness unit (candela per square meter: 1cd/m<sup>2</sup>) 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).
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 you are seeing discolored spots in the 100 IRE pattern (at 50 IRE or 100 IRE), try doing an external degauss.