The Color Dither Monitor Calibration Chart

Below is the latest version of the Color Dither Monitor Calibration Target in PNG format (since the GIF does not hold all the discrete color values of it, the gMA chunk is disabled). This chart is the optimum for systems that are used mainly for Web publishing.

The target has the following sections:

• On the far left: Gray gamma comparison swatch. With a perfect gamma match the left and right portions of the swatch have the same luminance.
  
• In the center: R, G and B gamma comparison swatches side by side. With a perfect gamma match the R, G and B swatches all appear as gray with the same luminance.
  
• Top right: High level blackpoint evaluation, the pattern must be (barely) visible.
  
• Bottom right: Low level blackpoint evaluation, the pattern must not be visible.

In accurately calibrated gamma 2.5 space and with accurately set blackpoint in any native (unadjusted gamut (just like the AdobeGamma calibrates) the chart appears gray (achromatic, without color) all over, the left and right portion of the left swatch have equal luminance and the left, center and right portions of the swatch in the middle also have equal luminance.

In case of gamma error or black-point error (Brightness control of the monitor) the chart will show either red, green and blue hues or cyan magenta and yellow hues.

The benefits of this chart are that:

1. the vision is much more sensitive to the color comparison than to pure gray comparison
2. it gives good visual feedback for the full dynamic range of the monitor.
3. it allows to calibrate gamma difference between the red, green and blue guns of the CRT extremely accurate.
4. it makes the black-point adjustment very accurate, it is not possible to arrive a good gamma match when the blackpoint is not close to the correct value.

Evaluate the gamma swatches at such distance that the dithering is fully averaged by the eye.

The Blackpoint sections

On the right the target has two black-point calibration sections:

• Top right: High level blackpoint evaluation, the pattern must be (just barely) visible.
• Bottom right: Low level blackpoint evaluation, the pattern must not be visible.

Even if this blackpoint evaluation is rather accurate in most viewing situations and with most of the monitors but still it has to be regarded as indication only. The proper way to calibrate the blackpoint is explained here.

Note 1: When this target is loaded into the Photoshop it will undergo the currently active color-management conversions so it will not function as it was designed. The correct place for the target is the desktop background.

Note 2: There can be (or usually is more or less) faint vertical hue-error at the edge of the vertical sections in the gamma wedges. It is more irritating with a low quality monitor and is due to the slew rate and stabilizing time problems in the signal amplifier in the monitor.

Note 3: It is a good idea to set the background color to R=G=B=0.

Note 4: If the target will not turn to all gray then there is gamma difference between the guns. In this case first concentrate on the leftmost gamma wedge (gray-dither, continuous-gray) and try to achieve lightness match as well as possible, then finetune the hue away with the individual color gamma sliders in AdobeGamma (or other such utility).

Calibration with Adobe Gamma

1. Set the above target as the Background image of the desktop.
2. Adjust the blackpoint accurately.
3. Set the Contrast control of the monitor to maximum.
4. Open AdobeGamma utility and set the Desired Gamma value to 2.5.
5. Adjust the gray slider for as good gamma match as possible.
6. Save the profile at this point, so that you can freely experiment how the color sliders affect to the chart.
7. Re-enter to AdobeGamma and now fine-tune any gamma mismatch that may remain using the color sliders and finally save the profile again.

Calibration without a gamma calibration tool

1. Set the above target as the Background image of the desktop.
2. Set the Contrast control of the monitor to maximum.
3. Adjust the Brightness control of the monitor on an uncalibrated PC system so that the chart shows as good gamma match all over as is possible.