[argyllcms] Re: Calibrating problems in darks areas

  • From: Klaus Karcher <lists@xxxxxxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Sat, 29 Dec 2007 17:38:41 +0100

On vendredi 28 décembre 2007, lee scratchy wrote:

yeah it does have RGB levels options, just set the color temperature to
USER, then you can play with BLUE and RED levels.

Frédéric Mantegazza wrote:
Ok, another point I missed: I though these sliders were controling the gain, not the offset...

You are right: first and foremost they control the gain, but they also affect the black level (in particular on older CRTs).

I used them to set the white point. But them, black level is totally wrong. But if I use them to control black point, the white point will be wrong.

How can you set both?

Since your monitor has no user-accessible offset controls, the only chance may be to bring it to a television- or monitor-service. Usually CRTs have internal controls to adjust offset, gain, slope, focus, convergence, etc. The question is whether the effort pays off.

Don't expect too much from an old CRT. It's basically an analog device and in spite of internal reserves and drift compensation circuits, it is subject to deterioration. From my experience, a CRT used in commercial environment (>40h/week) is unusable for color critical tasks after approx. 5 years.

well did you try my banding test patterns ?

Yes: it is very visible on the green one.

The more you have to "twist" the monitor from its native behavior, the more banding you get.

Maybe it can help to drive the monitor less close to its limits: try to reduce the luminance to aprox. 80-90cd/m2 and see if there are improvements in black level and/or banding.

If nothing helps it's probably time to say good-bye to your CRT.


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