Gray Marked Colormap not showing overexposed

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Since commit "update Qwt 6.2" (5406432c) the live image for our cameras with the Gray Marked Colormap does not show the overexposed pixels anymore. I don't know how to solve this.

Cheers Thomas

Comments (2)

  1. M. Gronle

    Hi Thomas,

    it seems to be mainly due to rounding effects when the color maps are calculated. The ``gray marked`` color map is a linear color with color stops. Currently it is defined like this:

    Stop Position Color
    0.0 magenta
    0.0 white
    1.0 black
    1.0 red

    I could create some examples, where the magenta and red color is visible and other examples, where only one of these colors is visible and 3rd examples, where no of these boundary colors are visible. The same holds for the color bar, if it is displayed.

    To really fix this, some code has to be changed in the qwt code.

    However, it is also possible to add a certain workaround, where both boundary color stops (magenta and red) get some more “space” in terms if the stop position.

    I tested some values and would propose the following stop positions:

    Stop Position Color
    0.0 magenta
    0.01 magenta
    0.0100001 white
    0.0899999 black
    0.09 red
    1.0 red

    Using these positions, it is assured also for small color bars that the colors magenta and red are visible. However, it can happen, that not only the very extrem points are displayed in magenta or red, but also some values, that are very close to them.

    Would this be acceptable for you?

  2. thomas kipp

    Hi Marc,

    it would definitely better than now but if I got you right, it would mean that for a 12 bit camera the highest 40 values would be marked as overexposed, which is quite much. If you see a possibility to for calculating a better value (like not a fixed percentage but always the highest 2 or 5 values) it would be much better for us. But as a workaround your fix would already be a great enhancement for us.

    Thanks for your help.

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