Setting Quantitative Values for Brightness and Contrast

Hi all! This is my first post as I am having trouble with ImageJ. About a year ago, when analyzing photos, it seems like I could quantify the specific value for brightness and contrast on a photo prior to thresholding (first photo). Now, when analyzing photos, there is a histogram where changing the brightness and contrast changes a line on the histological plot (second, third photo). I am reviewing some work and would like to be able to adjust the specific value for brightness and contrast. Is this a feature anymore (ie. does it require a plug in, newer/older version of ImageJ, new software)? I have seen both representations on ImageJ’s website. My question is how do I go from using the histological plot to the option of setting specific values for brightness/contrast?

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Please help if you have any ideas to resolve this issue.

Have you tried to click on the “Set” button here?

Yes, pressing “set” only allows you to change the minimum and maximum. I was wanting to change the values of the brightness and contrast.

1 Like

Hi Easton,
Please note that altering minimum and maximum alters the brightness and contrast (Brightness → position of line determined by min and max relative to histogram of pixel intensities; contrast → slope of the line). Brightness and contrast don’t have absolute independent absolute values, e.g. just setting a brightness value of x would be meaningless without knowing the start and end position of the line.
Regards,
Volko

Hi Volko,

Thank you for the post. I thought in the past that there could be absolute independent values entered for brightness and contrast. It seems like this post on ImageJ seems to confirm that this is a possibility. (Brightness and Contrast - ImageJ). Do you have any other ideas on how to be able to do that? Having a specific brightness and contrast is preferred for me as I have to write methods on a research paper and having specific, repeatable steps is essential.

Thanks again,

Easton

Hey @easton ,

the website you linked mentions " Note: This page refers to the version of ImageJ2 currently in development."

I’m afraid this functionality didn’t make it to Fiji yet.

Best,
Robert

Hi Easton,
Few additional points to consider:

  • How would you interpret/define a brightness or contrast value of x? Note that altering the brightness causes a parallel shift of the line that maps the pixel value to the intensity of the displayed image. However, the brightness setting has no influence on the slope. So, the same brightness value could lead to different image appearance depending on the slope of the line. Similarly, the contrast alters the slope, but this is also only really meaningful if you know either the start or end of the display range. However, defining the min and max of the display range unambiguously defines the position of the line. So, I would define the min and max values (or define how you set them), which determines the apparent brightness and contrast range for the displayed image.
  • The display settings don’t actually affect any of the measurements as they don’t alter the underlying pixel values unless you apply the settings to the image. So, they only affect how the image is displayed. I would say there are relatively few situations that would justify changing the underlying pixel values, especially if you try to do any quantitative analysis.

Hope this helps,
Volko