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How to measure SD(standard deviation) of L, a*,b* in a ROI

Hi all,

wanna to know how How to measure SD(standard deviation) of L, a*,b* in a ROI? try to select st dev for region color a, but it seems do not work...         many thanks~


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    Hi Louis,

    The stats combobox in the Measurement types dialog is for Multi-value measurements, such as Radii or Diameters, it cannot be used with single value measurements, such as "Lab color a".

    If you want to measure Std.dev. of Lab colors, you have to use other steps:
    1. Convert your image to "Color FPoint" to handle whole range of Lab values, including negative.

    2. Extract the channel of interest using L*a*b* measure dialog

    3. Optionally reset range of the new floating point image to see negative and positive pixels:

    4. Create measurement areas and measure "Intensity (Std.dev)"


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    Hi Yuri,

    Thank you very much for your guidance.

    I tried your method, but how to define the range of BL and WL to keep the value of l a b is the same as the original picture. it seems always scaled in some extent, and the value is different as in original pic. the same question also when we convert the pic into color FPoint, should i select direct copy pixel values without click apply best fit box?

    Thanks again and look forward your reply

    Best wishes,
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    Hi Louis,

    Yes, converting image to FPoint you must use either Scale or Direct copy (without best fit) options to preserve original image display range.

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