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What is the best way to calculate color difference in RGB, particularly for red?

I have images of a burn taken over two weeks, and I want to calculate the change in color over those 2 weeks. I am particularly interested in redness. I measured Intensity, red using Image Pro Premier, but I am having trouble making the numbers make sense. I subtracted the baseline (pre-burn) from the final and divided that by the final minus the burn, hoping to get a percentage of redness reduction. The numbers don't match what I am seeing in the image. Sometimes it's over 100%. Is there a different equation I should use? Should I use a different measurement type? 

Best Answer

  • edited February 2019 Accepted Answer
    Color Correction and L*a*b measurements are available in Image-Pro 10 and above, you may check how to update it to the latest version.

    You may also measure redness on white-field images using "Intensity Blue" or "Intensity Green" as me and Matt mentioned. (the lower Blue, the higher redness)

    Yuri

Answers

  • edited February 2019
    Hi Kristi,

    I can see that you have color references at the bottom of your images. You should use Color Correction tool of Image-Pro to match one image to another before doing color measurements. (use all 7 points on the color patch to do color correction).
    Then you can use any color measurements (Color category of the measurements):

    You can try all of them to see which one gives you the biggest difference.

    Yuri 
  • Kristi,

    Note, that if you want to evaluate color difference between Red and White, don't use R-channel (Intensity Red), because for both colors (White and Red) "Intensity Red" will be 255, use other component colors, such as Blue to measure the difference.
    And, as I mentioned in the previous post, just check all available color measures in Image-Pro to find the best.

    Yuri
  • Thank you, Yuri! How do I do a color correction?
  • I didn't extract the red channel. I kept the image as is and then measured intensity red. So that doesn't tell me how much red is in my image?
  • Kristi,

    Please check "L*a*b* Color measurements and Color Correction" page in Image-Pro 10 help. It contains the workflow with examples:

    Yuri

  • Kristi said:
    I didn't extract the red channel. I kept the image as is and then measured intensity red. So that doesn't tell me how much red is in my image?
    Yes, that's correct. You should not use "Intensity red" measuring redness on white-field image, it will not give you anything useful.

    Yuri
  • 2019-02-18-111504

    Kristi --

    I think what YURI is pointing out is that RED is an absence of GREEN, and BLUE (in the RGB COLOR MODEL).  This can be seen below where there are 5 colors that use the same RED (255) and different GREEN and BLUE VALUES.  In the first and last combination, the R = G = B and the result is on on the GRAYSCALE SPECTRUM because there is really no "COLOR" information in that "COLOR".

    This is why YURI is pointing toward measuring the G and B in the ROI rather than measuring the R.

    I hope this information is helpful.

    -- Matt

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  • I have Image Pro Premier 9.3, in which I can't find the color correction and L*a*b* help. How can I access that information for 9.3? I also have the images in a red format to show hemoglobin. Does this change how I should measure the red in the image?
  • Thank you, Yuri and Matt! As you can probably tell, this is quite new to me.
  • Are blue intensity and green intensity the type of numbers that I can calculate a change from baseline from and have it mean anything? I would like to show redness reduction.
  • Increase of "Intensity Blue" will indicate redness reduction (assuming that the base and test images are taken at the same conditions or normalized, having matching intensities/colors of the reference patches). Also, you can use "Saturation" - smaller the value, lower redness.

    Yuri
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