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Image color comparison


I have a question concerning Labview and Image Comparison.

I would like to know the best way to compute Comparison Image Color (or brithness).

I am acquiring 2 Images at different time with my camera and will like to find out if there is a difference in their Color (or brigthness ?). Using absolute Subtraction of both Images, i can find out if there is a difference between them. but when the difference concerns only the Backgroundcolor or brigthness, how is the best way to represent it. That means if both Images have the same Elements, but differs in their Color, what is the best way to find it out.

I can not use Color or Pattern Matching here because i don't have any Pattern. I am trying to identify any Change of state on a live Screen. I did the first part. Now i want to know how i can Show if it is only a Change of Color or brigthness.


I will be pleased if someone has any solution.


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Message 1 of 5

You need to learn more about Images and also about Color Representation.  Your question is difficult to answer, in part because it is "ill-formed".  Consider two pixels in a GrayScale image -- they either have the same U8 value or they don't, i.e. they may differ in "shade".  Now consider two pixels of RGB Color, represented by 3 (or 4) U8.  They either have the same array-of-4 U8 values or they don't.  But now what is different?  The color?  The "brightness"?  Color can be expressed in several different "scales" (RGB, HSL, HSI) -- look up Color Spaces.


You need to learn more about images and image representations -- it can be multi-dimensional in "interesting ways".


Bob Schor

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Message 2 of 5


here are two vis i implemented to registrate any Change of Color or luminance.

For Color comparison, i calculated the Lab Color Distance (Delta_E).

To resgistrate the difference of Luminance, i use Imaq Lightmeter and compare the Standard deviations of both Histograms.

the seem to be working. I wanted to know if there is a better or faster method to do this.


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Message 3 of 5


your code looks good to me. I’m not very deep in your project but on the first look I couldn’t find parts that would simplify your vi's.

I have found two examples that may help you. You can find them by searching in LabVIEW after them.



CIE Lab Color


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Message 4 of 5

Hey, Thank you for your reply.

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Message 5 of 5